A
LITTLE
BOOK
OF
MONITOR
LIZARDS
A Guide to the Monitor Lizards ojthe World and their Care in Captivity
~-
,~-
-\:
< •.
i.
by Daniel Bennett
In Memory of Patrick Joseph Price 1958- 1988
Many people helped me with this work, directly or indirectly.
I refrain from naming them in order not to embarrass anyone. Their
help, enthusiasm and hospitality are cherished and appreciated.
Special thanks must go to my mother, without whom
nothing would be possible
First published in 1995
© Daniel Bennett 1995
All righls reserved . No pan of this publication Lnay be reproduced, slored ill a
reuieval system or transmiued in any ronn or by any means, electronic,
pholocopying , recording or otherwise withoul the wrillen pennission
of the copyrighl holder. Every carc has been laken in the compilalion
of Ihis book. but the publisher can assume no responsibility for any errors
or omissions , or any effeclS arising therefrom.
Brilisb Library CalaJoguing in Publicalion Dala. A calaiogue record
for this book is available from the British Library .
ISBN: 095266320 1
Published by:
Viper Press,
P.O. Box 10087,
Aberdeen AB2 2GJ ,
Great Britain.
A large font version of this text is available from the publishers on request.
CONTENTS; I. AN INTRODUCTION TO THE FAMILY V ARANIDAE............ ................ ..
................7
2. THE HISTORY OF MONITOR LIZARDS.
Extinct monitors ..... .................... ..... .. .. .................... ......................... .. .............. ...... ..... .. ... ... ........ . Living monitors...................................................................................................................... .
.. .. 10
14
3. THE INSIDES AND OUTSIDES OF MONITOR LIZARDS
Metabolism ..................... ................... ........................... ........... ......... ..... ............ ........... .. .........
Heal......................... .......................................................................................................................
. ........... I 7
....... 19
Water .... .. ................... ....... ... ... .... ... ....... ... ..... .... ....... ................. .. .... ....... ............. ................... ........... ........... 20
Smell & tasle............ .............................. .............. ............... """ .. " .... ,, .. "" .......... " ........ "." .... " ..... " .... .. "".21
Sight ................................ " .. .... ......... ... ................ " .... ...... .......... ...... .. .. ....................................................... 23
Hearing ......................... .. .. ........ ............. .. ...... .. ........ ...... . " ................. .. ..... ........... ............................ .......... 23
Touch.... ..... ............ ... .................................. ............... ... ............ .. ....... .. ............................... ......................... 24
Size...... .. ...................................................................................................................................................... 24
Teeth & skull ...... ..... .......................... .. ....... ....... ........ ..... .......... ....... ................. ............... ....................... ...25
Noslri Is ........... ....... .............. , .............. ........ .................... ................... .................. ....... ..... .......................... 2 X
Feet & daws.............. .. ........ ............. ....................... ................... .. ................ ... ...... ....... ......................... .... 2X
Tails..................................................................................................................... .... .............. ...................... 30
................11
Colour & panern ............................................................... .................. ....... .............. .. . . 4. THE LIFESTYLES OF MONITOR LIZARDS.
......................... ......................... .. .....11
Defence.................................................................... . 14
Movement and shelter ................................ .. ............ .. ...................................... 36
Feeding.... .............. ... .................... ..... ..... .... ..... .... ........................ .... . Soci:~ behaviour. ..... .... .......................... ............... .......... .. .................... . . ................................... .4U
Reproduction ... .. .. ............... ................... .......................... ................... .. . .................... ..................... .. ....,4U
5. THE MONITOR LIZARD AND MAN.
Monitors in folklore and an.............................................................................. ......... .. ... ........................... .47
Uses of monitors by man ............................. ..... .. .............. ......................... .. .. .. .......... .... ......... .... ................ ..49
Use of man by monilOrs ........... ....... .. .......... ............... .... ... ...... ............ ........................... .. ........................ ..... 53
6. THE MONITOR LIZARDS OF THE WORLD:
Varallus acanthurus ............................................. ............ ............................. .................... .......................... 54
Varanus albigl/laris ............................................ .................. ................................................................... .... 56
Varanus buritji ............................................................................................................................................. 59
Varanus bercurii .................................................................................................. ....................................... 59
Varallus bengalensis ................................................. ........................................ ............ .. ................... .. ....... 60
VarCl/tus bagerti.................................................. ......................................................................................... 64
Vara/tus hreviwuda.............................................................................................................. .... 64
Varanus mudolinearus ................................................ ................................................ .... ............................ .65
Varanus doreanus .................................................................................... ................... .. .......................... ....66
Varanus dumerilii .................... ..... .................................................. ...... .................... .......... ....................... .. 66
Varallus aemius...................................................... ........... ........................... .. ................................ ........... 6X
Varallus exanthematicus ............................................................................................................................. .6'1
Varallus flaves' ·ells .......... ..................................................................................................... ....................... 72
Varallus flavirujus ... .... ..... ............. .... ............ ........... .... .......... ..... ......... ... .. ..... .... ....... ...75
Varanus giganteus ............................................................... ...... .... , .... ................... "'''''''''''' ...... ............... .MO
Varanus gilleni..... ... ........ ......... ........ ................ ....... ............................................................... X2
Varallus glauerri.................. ......... ....................... ... ............ ........ ... ................... ......... H1
Varanus glebopalma.............. ................. ........................................................................... ... X4
Varanus gouldii................................................................... ... ........ ................. ... "".. ""." .. "... ..X5
VurCl/IllS griseus.. ........... "" ....... " .. " .."............. ...... "".. ". " .. " ""XX
Vurufills illdif.'us . .. ...... ............ .
n,
I))
\ ! OJ'f1I1f1S
johi('nsis ........
... ....................... .... ...... ..... ...... ......... .... .. ... ....... ................. .98
\ : orOllftS
/.:ill!!or/tn'....
.. ........... .. ............................................................................99
\ 'O/,{l/IIiS
/.:tlmor/o(''' sis...... .
I '{I/tll/IIS Inl'rf('l/si "oraI1I1S nlifl·h ('/ Ii ...
.. ............................................................................................99
................ .... ........................................................ ........ .. ... 102
..... .. ..... ... . .. ...
.. .. .... ... ..... ... ...
....... .. ..............................
. ............. 104
........................................................ .. ......... 105
\'arUlIrt.fi ni/ofiells .
. ........................... ........ .. ........... 109
\:f/UUIIU ofin/l'(,lIs...
......................................... 112
VurOIllH /Ii/naf(,1I.fiis. .
. ................. .. ................................................... 112
Varun/iS "r(lsinus .. \I(I"(/IIf(.~ "/,i,,,orriills.
.. ........................................ ........................................................ 111
. ....... .. .................................................. ........ ... ........... 114
\'ol"al/us r(lS(,1I/)crRi .. Varul/us tluii('olli.'i....
....... ................
.......... ... ................................................. 116
.. ............................................................................................ 117
\'oral/ lts soh·orin,.;;
............ .......
1 /(J"(lllu.~ SU/\'(}lnf
.. .. .. .. .... ... ......... ........... .... ....... ..................... . . ........................ ..... . 119
. .................. .. ................. .. ................................................................................ 123
.. .. .... ... ..................... ....................... ...................... 124
.......................................... , ........................................................... 12.5
.., ................................... ....... ............... ............. ......... ....... ................ ...... .... 12.5
\/arU1IIIJ J((}/ariJ .... \ '"rO"IIJ J('m;r('m(' x. . \IOftl"IIS Jinli'iJ \ 'ora1lUS .fi/Jef/t·('f; ..
\'arunlls s(orr;............
. ... ............ .. ................... .... .. ....... , ....................... ........ ............... ................. 126
\'a l"U"UJ tclellcslcs ....... ............................................................................................................................. 127
\Jura"us fcrjue .. . ........ . ............................... .. ...... ................................................. 12R
VuruIIIIS lim(J,.e1f .~;s ........ ...... .. ..... ............................,........................................,......... .... ............................ 12R
"afolllls 'fiSI;S .. ..... .... ........... ....... .......................... ........ .... ..... .. " ............................................................... 129
\ ' arUlIll.f. \,ur;lt5
Varo""s ycmcnensi.ft ..
..................
.. ...................................................................................... 112
.. .................. .... ...... .............. ........ ....................................................... 134
7.KEEPING MONITORS IN CAPTIVITY.
Safety. .. .............................................................................................. ,................ ... 137
HD\lsing... . ... ... ....... ........... ........ ..........................,.......................................................... ....................... 142
Furnishings. ....... ............... .......................................................................................................... 145
Heat ................................................... ...................................................................................................... 14R
Light .......... .................................................. ......... .. ............................................................................ ....... 150
Water ...................................................... ......... ........... .............................................................................. 151
Diel ........................................................................................................................................................... 151
Disease ...................................................................................................................................................... 158
H. BREEDING MONITORS IN CAPllVITY.
Sexing MonilOrs ............................... ........ ................................................................................................. 161
Hnusing Monilors togelher ......................................................................................................................... 163
Triggering hreeding .............. ..... ..................... ............. ............... ........................................... .................... 163
Courtship and Maling ......... ....................................................................................................................... 164
Egg laying................................................................................................................................................... 165
Egg Incubation ........................................................................................................................................... 165
Carc of Ihe Ynun g...................................................................................................................................... 166
9. THE FUTURE FOR MONITOR LIZARDS ............................................................................................ 16R
APPENDIX I:GLOSSARY APPENDD< II: FURTIlER INFORMATION BihliogTilflhy Useful Socielies and Publications. APPENDIX 111: CLIMATIC DATA APPENDIX IV. CONVERSION TABLES APPENDIX V: CONSTRUCTION OF A SIMPLE CHIPBOARD ENCLOSURE
FOREWORU Monitor lizards are extremely exciting animals. Without doubt they look more like dinosaurs than any other living creatures. They are aggressive, carnivorous, intelligent reptiles and although some are true giants, others will fit easiJy into a matchbox. Large monitor lizards are found over almost a third of the Earth and so it seemed incredible to me that I could find so little written about them. With a lot of help from library staff I read as much literature as I could find about the monitor lizards. I tracked down the authors of much of the work and besieged them with questions. Then I visited and interrogated reptile breeders. Despite the naivete of many of my questions my requests were treated with great courtesy. The more I learned about monitor lizards however, the more I knew I didn't know. Some of the most important aspects of monitor lizard biology are still virtually unknown. Indeed , our knowledge of even the larger monitor is so incomplete that new species are still being discovered with regularity and virtually nothing is known about some of the commonest members of the family. This little book, therefore, is intended to be an introduction and guide to the wondrous variety of monitor lizards with emphasis on their ecology and care in captivity. The information has been provided by people who have worked and lived with monitor lizards. in the wild or in captivity. Much of it has been published before, but it is scattered widely through the literature and disguised in about half a dozen languages. With the exception of some minor articles of my own, to which I have given undue prominence, I have tried to omit any speculative material and have been obliged to ignore a lot of good information when the identification of the animal under discussion is in doubt. With the exception of proper names. I have tried to keep scientific terminology out of this book altogether and a glossary and conversion tables can be found at the back. In the last five years there has been an explosion of interest in the monitor lizards and this is reflected in the huge amounts of new literature, much of which is not covered in this volume. This little book of monitor lizards is designed to be a summary of our knowledge of these magnificent animals, both in the wild and in captivity, but it is by no means complete, nor does it claim, in any way, to be an authoritative work. It is to be hoped that in the near future some of the people who have had most success and experience with keeping monitor lizards will publish much more competent and thorough guides to their care in captivity. making mine memorable only for its modest price and more outrageous mistakes. Daniel Bennett Glossop. June 1995. Postscript Four months ago I underestimated the amount of recent literature published on monitor lizards. I have attempted to include as much of it as possible, as well as some papers that are not yet been published. but were very generously provided by the authors. As a consequence some minor typographical errors have been overlooked and remain in the text. I hope that readers will forgive me for them. D.B ., Aberdeen , September 191)5 .
5
INDEX OF COMMON NAMES Argu~ goanna s('(' V!!ollldii Asiatic w~ter monitor S(,('
Gillen's goanna see V.!?il/eni Glauert's goanna see
V .w/\'(/Ior
Vglollcrti
Banded tree goanna
S('('
Vsm/aris
Beccari's monitor sc(' Vh('c('ari
Bengal monitor S('(' V.l),.n!!a/rnsis
Black-headed goanna
,1'('('
Vlrislis
Black tree monitor ,1'('(' Vh{'( {'(/ri & V.ho!?('rti
Blue-nosed goanna
Vsemiremex
V.rudicollis
Kalabeck monitor see V.indicus & V.doreanus Karl Schmidt's monitor see
Blue-tailed monitor see
V.johieflSis.
Blackjungle monitor ,1'('('
V .eremilL~
Goanna X see V jlavimflL~ Racehorse goanna see Gould's goanna see V,gollldii V tristis , Vgouldii & V jlaviru,flls Rock leguaan see Gray's monitor ,I'('C Valhigularis Volivac(,lIs Rosenberg's goanna see Green tree monitor see V.rosenbergi Vprasi l!lL~ Rossellsland monitor see Grey Monitor S('C V.!?ris(,lLv V.telenestes Rough-necked monitor see Harlequin monitor see Vrudicollis Vrudicollis Rusty goanna see
,1'('1'
VI('riae
Pygmy desert goanna see
Salvadori's monitor see Vsalvadorii
Blunt-nosed goanna see
Sand goanna see V jlavirufus Kings' goanna see Vkin!?orum Savannah monitor see Komain monitor see Valbigularis &
VprimordilL~
Vsalvator
Vexanthematicus
Bos\.:'s monitor see
Komodo dragon see
Vexanthematicus
VkomodoeflSis
Sepik monitor see V.jobiensis Short-tailed goanna see
Vdormnus
Bogert's monitor ,1'1'1'
Koniecznyi's monitor see
V.brevicauda
Vho!!erti
V!?riseus koniecznyi
Spiny-tailed goanna see
Lace goanna see V.varius
Spotted tree goanna see
caSpilLv
Mangrove monitor see
Stripe-tailed goanna see
Clouded monitor see
VindiclLv
V.caudolineatus
V.hen!?a/ensi.~
Mertens' goanna see
Storr's goanna see V.storri
Bulliwallah sce V.mertensi
V.acanthurus
Caspian monitor ,1'1'(' V.!?riSl'lLV
neb,doslLV Crocodile monitor see V..w/vadarii Cuming's monitor see V..wlvator
V.similis
V.merteflSi
Mitchell's goanna see V .mi tchelli
Timor monitor see VtimoreflSis, V.scalaris &
I
Mournful goanna see V.tristis V.similis Mulga goanna see V.gil/eni Tree crocodile see
Desert monitor see V.griseus Dumeril's monitor see
Nameless goanna see
Vdumerilii
V jlavirufus
Tree leguaan see V.albi!?u/aris Twilight goanna see
Nile monitor see Vniloticus
V.glebapalma
V.salvadorii
Emerald monitor see VprasinlLv
lOra see V.komodoeflSis
Rute monitor sec Vrudicollis IPeaCh throated monitor see Freckled goanna see Vtristis V.jobieflSis Perentie see V!?i!?antelL~ Giant Goanna see Me!?a/ania Pilbara goanna see
I
l"i.H·O
Vpilharensis
1
An Introduction to the Family Varanidae
Monitors are a small but diverse group of lizards. They have been around for at least seventy million years, have probably lived on all of the Earth's continents and are still present in three of them . Monitor lizards are carnivorous and generally feed on any animals they are able to swallow. The family includes the largest lizards that have ever walked the Earth. But whilst some are gigantic creatures capable of preying on man, others are so small they have difficulty overpowering anything much larger than an grasshopper. Some of the largest lizards that ever walked the Earth still alive today . Most monitor lizards are only active during the day and all reproduce by laying eggs, but they employ a wide variety of reproductive strategies. The monitors show astonishing variation in size. diet, behaviour and habitat, and are a marvellous example of how one tiny group of animals have adapted to suit many different environments. The smallest monitor lizard reaches a total length of only 20 cm and a weight of less than O.OSkg (SOg). The heaviest monitor weighs as much as 2S0kg. The longest monitor lizard has a supposed total length of over 47Ocm. Monitor lizards inhabit areas which are among the driest and wettest places on Earth and are often present in large numbers. They are found in deserts. on seashores, in woodlands, grasslands, rivers, lakes, swamps and rainforests. Monitor lizards are extremely important to the economy of people, acting both as pest controllers and as a source of meat and leather. Some monitor lizards have been almost completely unaffected by the emergence of mankind (a few !)ave even benefited from it), but others have suffered extermination to the point that it is reasonable to suppose they will be have vanished from the wild before the end of the next century. Despite their size and their ecological and economic importance, the monitor lizards have not been given the attention they deserve by biologists. In recent years the siruation has improved greatly, but even now virtually nothing is known of the ecology of many species, including some of the largest ones. The purpose of this book is to surrunarise what is known about the way of life of monitor lizards in the wild, and how that knowledge may be applied to their captive propagation. Monitor lizard can be extremely rewarding animals to keep in captivity but, in my opinion. there is little point in keeping wild animals confined if they do not reproduce. The day may come when some of the monitor lizards will disappear for ever if they cannot be bred in captivity. Even small scale propagation of some species could make a significant contribution to their overall populations as well as providing important clues to their life history in nature. In the animal trade captive bred examples of even the commonest species are in great demand and fetch much higher prices than their wild counterparts, but they are all too seldom seen. For these reasons special emphasis has been put on the care of monitor lizards in captivity, and infonnation regarding their propagation is included wherever known. Again certain cases have been omitted either because they are suspect or impossible to verify and many more have been inadvertently overlooked. There is a wealth of unpublished data which would be of enonnous value to would-be varanid propagators. If you have experiences of keeping monitor lizards, good or bad, you should share them. Herpetologists are renown for being amongst the friendliest people in the world and herpetological societies provide an ideal way to meet, share ideas and learn from other enthusiasts. A list of some groups and societies with a special interest in monitor lizards is given at the end of the bibliography but is 7
Little Book of Monitor Lizards by no means comprehensive. Contacts for local societies can be found in magazines devoted to rertiles, or ask at a local zoo or museum.
NAMES ANn InENTIFICATION There are two explanations of the origin of the common name "monitor lizard", The Oxford English Dictionary attributes it to the belief that they gave warning of the vicinity of crowdiles. A more likely explanation is that the Arabic term for a lizard "ouaran" became l:onfused with the German verb "Warane" (to warn), hence the scientific name Varanus and the English term monitor (Lydekker in Stirling 1912). In parts of the world colonised by Europeans the monitors were confused with the large lizards of the Americas, the iguanas. Henl:e in Australia they are known as goannas. and in South Africa they are known as leguaans. Easy identification of monitors is hampered by two things; dramatic differences in the appearance of young vs. adults and geographical variations in colour and morphology, particularly in species which inhabit a wide range. Scientists often rely heavily on scale counts and characteristics to distinguish species. Unfortunately it is utterly impractical to count the scales of animals seen only at a distance, or those of captives, particularly of the very large and very small varieties. I have avoided detailing the scalation of the monitors except where no other characteristics will serve to distinguish species or subspecies. This information can be found in the literature cited . Keys to distinguish monitor species can be found in various works of Mertens (translations in Funk and Vilario 1980), Storr (1980, et aJ 1983) and Vernet ( 1(84). Difficult to spell and impossible to pronounce, scientific names are cumbersome and tongue twisting, but essential. Even today much information in the literature is wasted or misunderstood because of confusion over the identity of the creatures concerned. Scientific names are used as little as possible here, but their use is vital for correct identification of different species because common names (e.g. "water monitor") are often ambiguous. Monitor lizards belong to the family Varanidae. At present all living species belong to the genus Varanus and all other recognised genera are considered extinct. The generic narne Varanus is often abbreviated to V. and the specific name written in its entirety, e.g. V.tris/is. Between the generic name and the specific names a subgeneric narne may be inserted in brackets, e.g. Varanus (Odatria) tristis. After the specific name there may be a subspecific name, e.g. Varanus (Odo/ria) tristis orientalis. In some cases the subspecific name may eventually replace the specific name if the animals are thought different enough to warrant being recognised as separate species, e.g. Varanus (Odotria) orientalis. It is possible that the genus Varanus will be split into a number of smaller genera before the end of the century, because some people consider the present classification to be too simple. In this case the subgeneric name may replace the generic name, e.g. Odotria tristis orientafis or even Odatria orientalis. The name is followed by the author and date of the animals' original description, in which he or she nominated a single, pickled, lizard as a typical example of the race. This unfortunate creature is known as the holotype. In the past many people have named animals without being aware of previous descriptions of the same species. In this case the name of the oldest existing holotype is given priority. Many monitor lizards have been renamed. or even unnamed, in recent years. In addition many monitor species remain undescribed. A useful list of poorly-known monitors and unknown species can be found in Philippen (1995).
8
Introduction
Where scientific names are completely useless is in the areas where the lizards actually live. For example, a monitor lizard from Africa is known as eikwambo, mbulu, gruza, awonriwan, kgwate, uxamu, mampan-tintin and at least a hundred other names, but very few of the people who are acquainted with it in nature are aware of Linnaeus' description of the species in 1758 and the subsequent revisions that led to the name Varanus niJolicus. This is unfortunate for us, for they are the people who know most about it and can contribute best to our knowledge of its natural history. Much can be learned about the ecology of monitor Lizards even on a family holiday, by questioning knowledgeable locals. Knowing the local name for the animal you are interested in and having a good clear photograph of it are essential to avoid misunderstandings. They will probably be happy to show you the animals living wild and give you the most memorable moments of your holiday. As our understanding grows, so does our respect for those with whom we share the planet.,; who were here long before us and may be here long after.
<)
2
The History of Monitor Lizards
As the monitors spread across the Earth experiencing different habitats and climates they diversified. Over many millions of years this process has resulted in the emergence of at least seventy or eighty (probahly many thousands of) species. Some of them appeared to have died Ollt quickly, whilst other, apparently ancient, species have survived until the present. Many monitor li1.ards appear to have evolved comparatively recently. It would be nice to know where the monitor lizards first came from, what the early species looked like, how they hehaved and why they died out. Fossils provide us with a tantalising glimpse of a world that we will never know. They have the unerring ability to create more questions than they answer. The chances of an animal or plant being preserved as a fossil is extremely slight. It must be covered with a protective layer as soon as it dies and many miUions of years later it must somehow get back onto, or close to, the surface of the rock . Then somebody has to find it. The vast majority of known fossils come from marine organisms, only a tiny proportion are of terrestrial vertebrates and the monitor lizards are poorly represented there. All the monitor fossils I have seen have been unexceptional. Our knowledge of this family before the dawn of civilisation comes from fossilised remnants which are sometimes nothing more than a single vertebrae or fragment of jaw. Often it is very difficult to tell what sort of animal a scrap of bone belonged to over 80 million years ago, with the result that whilst some authors will consider a fossil bone to be that of a monitor lizard the next may claim that it is in fact a piece of prehistoric tortoise. Fossils records of monitor lizards from Africa and Australia are very rare, probably reflecting the unsuitable conditions that existed for fossilisation rather than the scarcity of the animals. Thus this little "history" of the monitor lizards must be taken with a large pinch of salt. Except where indicate<1 the following account follows Estes (1983). We do know that by 300 million years ago at least three major groups of reptiles had established themselves on Earth. The synapsids included the lizard-like pelycosaurs, some of which closely resembled the monitor lizards of today (e.g. Varanosaurus from what were then the swamps of Texas) and the "theraspids" which may have survived to the present in the form of modem mammals. The anapsids include the living turtles and tortoises and other orders, all of which had died out by 250 million years ago. The diapsids gave rise to dinosaurs and other ruling reptiles as well as birds, crocodiles, tuatara, snakes and lizards. True monitor lizard-like animals (varanoids) appeared in the Late Jurassic era, about 180 million years ago. Aigialosaurs were small aquatic lizards that were probably closely related to the monitors. They gave rise to mosasaurs, a diverse group of water lizards growing up to 10m long that roamed the seas for over 100 million years before dying out altogether (Cox et (II I !)RR; Zug 1994). As they disappeared monitor lizards first appeared on the land. According to the available evidence monitor lizards and their close relatives the heloderrns (Gila lizards) and lanthonotids (earless monitors) probably originated in northern Asia at least !)O million years ago (Pregill et al 1986). At this time the reign of the dinosaurs was coming to an end and flowers had begun to cover the Earth. The oldest monitor lizards known are from Mongolia: Telmasaurus grangeri. Saniwides mongoliel1sis and Estesia mongoliensis. All of them must have been quite similar to modem monitor lizards in appearance, but the latter possessed grooved teeth which probably transmitted venom in the same manner as 10
HislOry of Monitors modem-day Gila monsters (Pregill cl al 1986, Norell el al 1992). The exact relationship between these lizards and the modern heloderms and varanids is not clear. Early fossils tematively identifie<:l as monitor Lizards have also been found in Alberta and Wyoming in North America. Most authorities agree that this part of America was still attache<:l to Asia when monitor Lizards appeare<:l. Paleosanawina canadensis Live<:l at least 70 million years ago and probably reached a total length of about 240cm (Gilmore 1928). These Lizards had long backward pointing, serrate<:l teeth that show grooves similar to those of the Mongolian Estesia. Although they too must have been very similar to the present day monitor lizards, their inclusion in the family Varanidae has been questione<:l. The oldest fossils defmitely identifie<:l as belonging to the monitor lizard family belong to the once widespread genus Saniwa which appeare<:l at least 55 million years ago. Describe<:l species include Safliwa enside/ls, S.grandis, and S.crassa from Wyoming, Spaucidens from Wyoming and Utah. S.brooksi from California, S.orsmaelellsis from Belgium and unidentifie<:l species from France, New Mexico, Wyoming and Nebraska. Apart from differences in size there is little to distinguish these fossils from each other, nor from living monitor lizards. Salliwa may not have survive<:l for long in Europe but they persiste<:l in North America umil at least 15 million years ago. The living genus, Varallus, does not appear in the fossil record until about 25 million years ago. The oldest fossils come from Kenya and Khazakstan and are too fragmented to be assigne<:l to species. The oldest European monitor is Varallus hoJmallfli , about 10 million years younger, which is known from France, Spain and Germany. At the same time the closely relate<:l Iberovaranus catalollicus live<:l in Spain and Portugal and Varanus pronini lived in Khazakstan (Zerova & Ckhikvadze 1986). V. marathofleflsis appeared at least 5 million years ago and is known from Greece, Hungary and Turkey. An unconfirmed record of this species from Italy suggests that the monitor lizards may have survive<:l in Europe until less than a million years ago. Orlov & Tuniev (1986) suggest that V.marathonellsis was very closely related to the living V. griseus and to V. darevskii, which live<:l in Tadjikistan about 5 million years ago (Levshakova 1986). V.semjollovi is known from Ukraine and another species, V.lungui has been dcscribe<:l from Moldavia (Zerova & Ckhikvadze 1986, Lungu et al 19X9). At this time a very large monitor lizard approaching 3m in length, V.silvalcnsis, Iive<:l in India. Other extinct fossil species include V.hooijeri. a close relative of the present day V.olivaceus, which live<:l on Flores less than 5 million years ago and possibly V.botkayi, known to have inhabite<:l Java and Timor about 2 million years ago (these fossils may represent the living species V.salvator (Auffenberg 1981)). Unfortunately vinually nothing is known of the monitor lizards' history in Australia. The earliest fossils known come from South Australia and are around 10 million years old (Estes 1984). Fossil vertebrae of a species similar to V.giganteus from New South Wales are less than 2 million years old. On immunological evidence Baverstock et at (1994) suggest that monitor lizards reached Australia from south-east Asia less than 20 million years ago. When monitor lizards reached Australia, something very strange happened to them. Throughout the world fossil monitors appear as large or medium sized lizards, but few, if any, ever exceeded 300cm in length. In Australia both gigantic and dwarf monitor lizards evolved. Megalallia (or Varallus) prisca was the largest lizard that has ever lived. Adults may have weighed over 600kg and measured more than 7m in length. They appear to have been widespread in Australia (remains have been found in New South Wales. Queensland and South Australia). II
History of Monitors This immane goanna is not a long dead and buried species. They may have survived until less than 25,000 years ago and are believed to have preyed upon the giant ancestors of kangaroos and wombats. Giant goannas may also have preyed on early human settlers, who must have regarded its extinction with great relief, even if they did not playa direct role in its demise themselves (Owen 1860, 1880, Anderson 1931, Hecht 1975 , Rich 1985, Molnar 1990). The artist's impression of the giant goanna given here does not take into account the fact that this enormous monitor lizard may have had a bony crest on top of its head. Other ancient Australian goannas include an unidentified species that lived in South Australia 5 million years ago and had very large blunted teeth (Archer & Wade 1976) and the fossil V.emeritus from Queensland , which may represent another extinct species. Recent fossils of the living lace and sand goannas have been recovered from cave deposits in Victoria (Wells et al 1(84).
Above: Meg!l/allia JiriIm (Stuart Dilks after Anderson 1930)
Opposite: The giant goanna meets its mat4:h (lain Curran).
12
£1
SJ01!\I0~)0 AJ01S!H
Little Book of Monitor Lizards Whilst some of the Australian monitor lizards became massive the more successful ones had adopted an opposite strategy. They shrank and diversified to form a unique group of diminutive varanids that spread throughout Australia and then began to move nonhwards (Storr I,;)XO). To date they have not got very far; to the south of New Guinea and a few islands in the Timor Sea. Nevertheless, they are a very young group of lizards and already account for two-thirds of the living species of the Varanidae in Australia, and a third of the family world-wide. The larger monitor lizards have also persisted in Australia with at least 9 species living there today. Today at least 46 species of monitor lizards are known to exist in Africa, Asia and Australasia . Baverstock el at (19';)4) suggest that all living species have evolved from a common ancestor within the last 45 million years. The confusion over the extinct varanids is unlikely ever to be resolved fully, but ample opponunities remain to study the surviving species. It is hoped that by examining many different characteristics of the living monitors it will be possible to gain some idea of how they are related to each other and evenrually, it is hoped, their di spersal routes and the chronological order of species evolution will become apparent. Monitor lizard taxonomy is a lively and controversial subject. For practical purposes, it must be possi ble to distinguish between species on the basis of external morphological characteristil.:s, but these criteria can be misleading. Species which inhabit many different habitats over a huge range often show great variation in colour, pattern, scalation, shape and size, and very small populations often show similar variation between individuals, even amongst groups of siblings. JList as it is not always possible to tell which monitors are closely related to each other merely by looking for similarities in their external appearance, nor is appearance always indicative of the animals' lifestyles, because species can develop independently of each other and in very different habitats, yet appear remarkably similar. A good example is the belief, held for many years, that the yellow monitor was a close relative of Bosc's monitor, because the species looked so much alike. Unfonunately for the marsh dwelling yellow monitor, it was also presumed that they shared similar habits, with the result that captive specimens were kept in quite unsuitable conditions and were unable to tlourish (Rotter 1963 , Vi sser 1985). It is now known that Bosc's monitor is a close relative of the Nile monitor, to which it bears little obvious resemblance, and that the yellow monitor is more closely aligned to the Bengal monitors and some other South East Asi an species (Bohille II)l)X). Over the last twenty years the accepted relationships between species of monitor lizard have been largely revi sed using a variety of methods, all of which have advantages and disadvantages beyond the scope of this book. In recent years a number of studies have examined less obvious characteristics of the monitor lizards in order to clarify their relationships with each other. They include studies of protein and DNA, examination of morphological I.:haracteristics such as lung and hemipenal morphology and shared behaviow'a l traits. There are some differences of opinion, but in general these studies differ only slightly from each other in their wnclusions. Unfortunately some species have not been available for analyses and sample sizes for many others are very small. Much more work must be done before we have complete and certain knowledge of these relationships. The following is a summary of the I.:oncurrent (and not so concurrent) points. FuU di scussions can be found in Merten s (11)42, I%3), King & King (1975), Holmes e/ at (1975), Becker (1991) ,
14
~
History of Monitors Bohme (1988, 1991), King et a/ (199 I) , Sprackland (1991 a), Baverstock ct a/ (1994) and Card & Kluge (1995). I.The African monitor lizards, V.a/bigu/aris, V.exanthematicus and Vni/oticus and Vyemenensis are currently classified as belonging to the subgenus Po/ydaeda/us. Some studies suggest that V.griseus (at present in its own subgenus, Psammosaurus) also belongs to this group. On this basis the expansion of Vgriseus into Asia could be interpreted as being relatively recent. Other studies suggest that V.griseus has no close living relatives, and should remain in its own subgenus. 2.The Asian monitor lizards V.benga/ensis / V.nebu/osus, Vflavescens, Vdumerilii and probably V.rudicol/is form the subgenus Empagusia.
3. Vk.omodoellsis appears to have its closest living relatives amongst the large Australian monitors, particularly Vvarius. According to recent studies these two lizards together with V.giganteus, V.rosenbergi, Vflavirufus, Vgou/dii and V.spenceri form a distinct lineage, the subgenus Varanus. 4. V.sa/vator appears to have no close living relatives (except possibly for Vrudicollis). However, "V.salvator" may be a conglomeration of several species (chapter 5). 5. Vsa/vadorii is the sole member of the subgenus Papusaurus (Mertens 1962). 6.The dwarf monitor lizards form a distinct lineage, (subgenus Odatria) which probably includes V.mitchelli (previously considered a Varanus-type animal). All Odatria are restricted to Australia with the exceptions of V.timorellsis and the V.scalaris type animals of New Guinea. One study suggests that V.eremius does not belong to this subgenus and forms its own unique lineage. The same study (Baverstock et a/ 1994) indicates that Odacria monitors can be divided into two groups, one containing the spiny-tailed monitors (V.acamhurus , Vbrevicauda etc.) and V gilleni, the other containing the long-tailed rock goannas (V.g/auerti, Vglebopalma, V.pilbarensis), together with Vrristis, V.sca/aris and Vmitchelli. The fact that dwarf monitor are found nowhere else is strong evidence that this group evolved in Australia.
7. Vindicus, the Vprasillus group, V.jobiensis and V.doreanus form the subgenus Euprepiosaurus. The centre of distribution of Euprepiosaurus is New Guinea, where all species are found. Only the highly aquatic Villoicus has extended its range over a much wider area; over much of the north coast of Australia and many of the islands of the South Pacific (due in part to mankind's' intervention - see Chapter 5 ). At present monitor lizards reach their highest diversity in Australia, where half the living species occur, including virrually all of the dwarf forms and many of the larger species. Nobody really understands why the monitors are so successful in Australia. The absence of large carnivorous mammals which would act both as predators and as competition for food resources is undoubtedly a major factor in their present distribution. Although in the past plenty of giant carnivorous marsupials have inhabited the continent the only large predators to have survived to the present in many areas of Australia are the monitor lizards. Perhaps their more economical physiologies and greater water-conserving abilities allowed them to survive when the marrunals perished. Unfortunately the past climate of Australia and the age
IS
Little Book of Monitor Lizards of its deserts is not a subject of universal agreement (Pianka 1986). It has been suggested that a massive decrease in rainfall leading to a "dry age" occurred in Australia within the last two million years, leading 10 deseilification and the demise of many animal species. However some of the Australian deserts which are home to large numbers of monitor lizards species may be very much older than this. I would like to think that the ability to stand and walk bipedaUy may have contributed to their success in Australia. Some Australian goannas use bipedalism to a much greater extent than other monitor lizards. Perhaps only the arrival of mankind, somewhat steadier on its hindiegs, prevented them from perfecting the technique.
16
3
The [nsides and Outsides of Monitor Lizards
Monitor lizards can be distinguished from all other lizards at a glance by their deeply forked tongues. Heloderrns and tegus also have forked tongues but they are less well developed. Furthermore these lizards have large scales on their heads whereas monitors have much smaller ones. Monitor lizards eat food that fights back and uies to escape and so are fast moving creatures equipped with sharp teeth and strong limbs. Most of their senses are extremely acute and they are considered to be the most perceptive and intelligent of the lizards. In many aspects of their morphology and ecology monitor lizards seem more closely aligned to snakes than to typical lizards. Like snakes they are able to swallow very large prey items whole and like many snakes they have a particularly well developed sense of smell. However there is no evidence of a close relationship between the monitor lizards and any snake (Joger 1991) and the remarkably similar attributes of these reptiles appear to have evolved completely independently of each other. The large size of these splendid lizards, combined with the relatively easy availability of many species, mean that monitors are often the subject of laboratory experiments. Most of the experiments conducted on them are related to their ecology only in a very roundabout way and are not discussed here. Useful works on the anatomy and morphology of monitor lizards include descriptions of the skull and other bones (Mertens 1942, Brongersoma 1958), teeth (Rieppel 1979), jaws (Sinclair & Alexander 1987), shoulder joints (Haines 1952), toes (Landsmeer 1981), skin (Fuchs 1977, Smith & Hylander 1985), tongue and throat musculature (Smith 1986), the snout (BeUairs 1949), the heart (Webb el al I
GENETICS All monitor lizard s studied have a diploid chromosome number of 40, consisting of 8 large and 12 small pairs. Females appear to be the heterogametic sex (King & King 1975, King el at I <)82) but there are suggestions that environmental conditions of incubation may have some bearing on sex determination (see Chapter 8). METABOLISM Like all animals, monitor lizards breath so that they can get oxygen in, and carbon dioxide out, of their blood. The oxygen is used in a complex chemical pathway that provides energy for the organism by "burning" food; carbon dioxide is a poisonous waste product produced by those reactions. In mammals and birds this process releases a huge amount of heat that keeps us nice and warm and able to function at any time of day or night. In lizards however, the heat produced is negligible, so that it can be seen as a rather more economical system, though not without its drawbacks. Although lizards need much less food than mammals of a similar size, they are dependant on heat from the sun and as a result their activity is smetly limjted by the amount heat available from their environment. Monitor lizards have the ability to generate a small amount of metabolic heat and when they are active they can be very 17
Little Book of Monitor Lizards active. The metabolism of some monitor lizards has been said to "bridge the gap in metabolism that has generally been assumed to exist between reptiles and mammals" (Bartholomew & Tucker 1964). Most monitor lizards have much higher metabolic rates than other, similarly sized, lizards when they are active, but use no more energy when at rest. They show an number of adaptations that allow the muscles to receive plentiful supplies of oxygen even under difficult conditions. Under normal circumStances muscles get tired because they burn oxygen at a faster rate than it can be supplied from the lungs via the blood. As oxygen consumption rises so does carbon dioxide production. The waste carbon dioxide dissolves in the blood and is carried to the lungs where it is expelled. But because it is acidic it lowers the pH of the blood and thus reduces the blood's ability to carry oxygen. The problem is partly solved by keeping supplies of oxygen stored in the muscles which can be used when the oxygen supply from the lungs becomes insufficient This supply is limited though, and results in the production of acids in the muscles wlUch further deplete the ability of the ti ssues to take up fresh oxygen. Monitor lizards are able to minimise these problems in a number of ways. They have very large and efficient lungs which are supplied with copious amo unt s of blood that contains proteins wlUch prevent the build up of acidic wastes. Furthermore the oxygen stores in the muscles are unusually rich and contain similar buffers that keep the acidity of the blood stable (Bennett 1972, 1973a,b). These and other adaptations, such as careful control over the rate of breathing at different temperatures and hearts that limit the mixing of oxygenated and deoxygenated blood (Webb et af 1971, Gleeson el af 1980, Heisler el al 1983) give many monitors lizards phenomenal strength and , most importantly, endurance. These adaptations are not limited to the larger species. The pygmy Gillen's monitor , for example, can run at I km per hour for many minutes without showing any sign of exhaustion (Bickler & Anderson 1986). Indeed the experimenters found it impossible to tire the lizards out on their treadmiU. Gillen's monitor is one of the smallest members of the family, with a weight of about 30g. It needs about O.2ml of oxygen per gramme of body weight per hour to keep itself alive. When strenuous activity is undertaken oxygen uptake can increase more than twenty five fold and the efficient transport systems ensure that it reaches the working muscles. The ecological significance of these adaptations are obvious. Species endowed with a IUgh metabolic capacity have greater stamina than any other lizards; they ca n run furth er, swim further , fight longer and dig longer. They are without doubt the athletes of the squamates. But although many monitor lizards have the ability to sustain high levels of activity for long period s and use more energy than li zards of other families (e.g. the desert monitor (Vernet el af 1988 a,b), white-throated monitor (Wood ('I af 1977, 1978), Bosc's monitor I (Gleeson el af 1980), Rosenberg's goanna (Green, Dryden & Dryden 1(91 ), sand goanna (Bennett 1972), perenrie (Green el al 1986, see also Thompson 1995), Gillen's goanna (Bickler & Anderson 1986) and the Komodo dragon (Green, King, Braysher & Saim 199 1)) it would be misleading to suggest that aU monitor lizards are endowed with supernatural strength and stamina, nor that they necessarily engage in lots of vigourous exercise. The spiny-tailed goanna (Dryden el af 1990, Thompson & Withers 1994), Mertens' goanna (Christian and Conley 1994) and possibly the water monitor (Gleeson 1981 but see also Dryden el al 1992) have lower metabolic rates that do not differ from tho se of "rypical" lizards. Monitors that spend time in water maintain lower body temperatures than other varanids, which may be responsible for their less vigourous metabolisms. The spiny-tailed monitor may ca tch more food by ambu sh than by actively searching for it and may not require as much strength and stamina as its more active relations
I As "V.ex(Llllh('m(1(ictls" -
presumed to be Bose's monitor on basis of size. IX
e:: e::
'II ~
Insides & Outsides of Monitors (see l:hapter 5). Rosenberg's goanna, though capable of sustained activity, may spend more than 23 hours of the day lying about, even during the height of its activity season (Christian & Weavers 1994). Even the most active species are very economical with their energy, reducing metabolism at night, remaining immobile for long periods when food or water are scarce and only hunting energetically when prey are plentiful. Some species are able to store large amounts of fat in their bodies which may be used to sustain them through long periods of inactivity (sometimes more than six months of the year), in seasons when they may be particularly active but have no time to feed and for the production of large numbers of rich , yolkyeggs. During periods of inactivity many body functions are greatly reduced to conserve energy. Red blood cell levels may drop to levels that forbid vigourous activity even if favourable conditions return unexpectedly (Banerjee & Banerjee 1969). Studies of metabolic rates in the field have important implications for the captive care of monitor Lizards. Adequate exercise is essential to keep the animals healthy but because of the seasonal nature of their activity patterns the artimals should be given the option to reduce their activity, sometimes for long periods, if they desire to do so.
HEAT. Like all reptiles, monitors have very Little control over their body temperatures and depend on heat from the environment. Activity is only possible within a narrow range of temperatures and when conditions are too hot or too cold the lizards must remain in insulated shelters. Some species never encounter adverse temperatures (i.e. those from moist tropical forests) but others only rarely experience conditions that permit activity. The need to alter behaviour according to thermoregulatory considerations restricts the Lizards' activity to a large extent but the freedom from having to use energy to generate body heat allows the lizards to be vastly more energy efficient than other vertebrates of the same size. The parietal eye, situated on the top of the head, is an important organ in thermoregulation (Kulshreshtha & Khan 1988). Temperatures of a number of monitors lizards have been recorded in the field (see chapter 5). Activity temperatures usually Lie between 22 -38°C with aquatic monitors having lower temperatures than other species. In some monitor lizards' body temperature drops sharply at night but others attempt to keep their body temperature relatively stable. At temperatures below 20 0 C monitor lizards become slow and at 50 C they become completely torpid (Spellerberg 1972). Expo sure to temperatures above 420 C for more than half an hour results in death. "Critical Thermal Maximums" have been recorded for several species of monitor lizard but much less is known about the lower range of temperatures tolerated by species that must survive cold winters. From the point of view of captive husbandry this is very unfortunate. It would be expected that desert monitors, who have to wntend with much higher and lower temperatures than their relatives in tropical areas, would be better able to tolerate fluctuations in temperature. Spellerberg (1972) suggests that lace goannas can withstand temperatures as low as -8.5 0 C for short periods. Rates of heating and cooling have been established for a number of species; Komodo dragons (McNab & Auffenberg 1976, Green et al 1991), lace goannas (Brattstrom 1973), grey monitors (Francaz et al 1976, Franl:az & Vernet 1978), Nile and white-throated monitors (Bowker 1984), Bengal monitors (Meek 1978, Earll 1982), Gould's or sand goannas (Johnson 1972) and water monitors (Meek 19n, Traeholt 1995),
19
Little Book of Monitor Lizards Monitor lizards usually fall into a deep sleep in the evenings and wake up at about the same time each morning, regardless of the weather. During the night body temperatures may have fallen too low to permit activity and so if conditions outside are not extreme they emerge from their retreats shortly after waking and move to a basking area nearby where they lie in the sun until warmed sufficiently. This can take between a few minutes to several hours. Monitors like to bask on surfaces that retain heat well. Some individuals of several species bask all slightly elevated patches of earth which they keep clear of debris. Other basking sites include tree branches, elevated rocks or mounds and road surfaces, which are often their downfall (e.g. Bush el al /991). If the weather is cool the lizards may bask for several hours and then return to their burrows, but if suitable body temperature are achieved they can commence activity. However they cannot spend long in places where the temperature is unduly hot or cold before having to seek out more equable areas. Burrows, tree hollows, bodies of water and thickets of vegetation usuaUy provide conditions that are cooler than ambient during hot weather and wanner than ambient in cold weather. Monitor lizards that like to maintain a reasonably constant body temperature can shuttle between open ground , dense vegetation, burrows, trees and water according to their heat requirements, coUecting food from each area. Monitors living in overgrown habitats such as rainforests, where there is little direct sunlight but air temperatures are always suitable for activity may do very little basking. Monitor lizards in the extreme northern and southern parts of their range (i.e. northern and southern Africa, southern Australia and central Asia) may spend more than half of the year in a donnant state. In contrast monitors that live in the tropics, where the temperatures are much more constant both from day to night and from season to season are active throughout the year, but expend most of their energy during the breeding season.
WATER Monitor lizards are able to conserve water much more effic iently than most other wrtebrates. Works on the water balance of reptiles usually make very dry reading, but Green & King (1l)<)3) provide a particularly engaging, lucid and comprehensive account of thi s subject. That monitor lizards vary in their abilities to conserve water is not surprising considering the variety of habitats they occupy. Species from areas where fresh water is always available dehydrate very quickly under dry conditions (Cloudsley-Thompson 1967). Monitors living in areas where freshwater is scarce, such as coastal region s and deserts must take mea sures to prevent excessive water loss. Physiological adaptations (di scussed in Green & King 1993, see abo Braysher & Green 1970, Green I 972a&b) ensure that very little water is lost as urine. In w'id areas the need to conserve water may influence behavioural patterns as much as tht:rmoregulatory considerations. The retreats used by monitor lizards to ameliorate temperature changes also help them to con serve water. The humidity inside burrows, tree hollows and plant thickets can be much higher than in open spaces. Some monitors remain underground for several months during the driest part of the year (e.g. Rosenberg's goanna (Green and King 1978), Bosc's monitor and the Nile monitor (Cisse 1971)) even though suitabk temperatures exi st and at least some food is available. The ability to survive on very little water may have been the crucial factor that allowed monitor lizards to persist in Australia when all other large carnivores perished. Tht: animals that art: eaten by monitors usually contain plenty of water, allowing the lizards go fo r long periods without drinking . However those that feed on marine animals ingest large amounts of salt which prevent water uptake and must therefore be eliminated from the body. Many species of mo nitor lizard possess glands ill the nostril that contain ionocyte cells which actively tran sport salts out of the blood and secrete them as very concentrated brine. In the
20
Insic1es & Outsides of Monitors case of the aptly-named rusty goanna these glands allow them to live in saltwater areas and feed on salty foods without ever having to c1rink freshwater (Dunson 1974). Many monitor lizards can inhabit saltwater areas and are often seen swimming in the sea (e.g. Neill 1958). This allows them to disperse rapidly through groups of islands and even to reach new landmasses shortly after their formation. Their unfussy diets enable them to survive in areas that would not support most other large vertebrates. SMELL, TASTE & BODY ODOURS. Smell and taste mean the same thing to the monitor lizards and playa very important role in social behaviour and in feeding. Their tongues are more highly adapted to detect scent than in any other lizard family and, like snakes, it has lost all functions other than its sensory one (although some species use the tongue to lick up small insects) (Mertens 1942a, Smith 1986) . Taste buds are present on the tongues of at least some monitor lizards (Schwenk 1985), but by far the most important olfactory organs are the well developed Jacobson's organ s, located near the tip of the snout. Active monitor lizards continually flick out their magnificently long tongues whilst active, and in doing so take samples of the air to the Jacobson's organs, which are paired so that each receives information from one fork of the tongue. Equipped with this very sensitive apparatus monitor lizards can detect faint smells. So faint in fact, that one species can smell carrion from as far as II km away when conditions are suitable. It is believed that the lizards are able locate the source of the smell by c1etermining whether the scent is stronger on the left or right fork of the tongue and moving accordingly (Oelofsen & Van Den Heever 1979; Auffenberg 1981). In many species eyesight is relied upon to find most living food. but it is never eaten without first being investigated with the tongue. ill many species this sense is relied upon to the extent that the lizards will swallow almost anything of a manageable size, providing it smells right. Aluminium foil and porcelain eggs (used to encourage chickens to lay) ha ve been found inside wild caught monitors, presumably because the former had been used to wrap meat, and the latter had been sat on by a hen (Luckhoff in Anon 1937). Wesiak (1992) that spiny-tailed reports monitors become so excited by the smell of blood that they will attempt to consume their own injured limbs. Mon.itor lizards can follow a prey animal's scent for considerable distances, and also hunt for food underground and underwater using their remarkable olfactory powers.
Tongue of the mangrove monitor 21
Lillie Book of Monitor Lizards Laboratory studies have shown that the rate of tongue flicking increases when food is present, and that the rate of tongue flicking remain s high for more than half an hour after the lizards have seized their prey (Cooper 1989, 1993; Garrett & Card 1993). Rattlesnakes show a similar behaviour whi<.:h is believed to be associated with the search for envenomed prey. Possibly the behaviour eJUsts in monitor lizards as a relic from the time when they themselves possessed venom glands (Chapter 2).
The social behaviour of monitor lizards is very highly scent orientated. Many keepers will deny it, but monitor lizards have a very distin ctive smell. Male water monitors will attempt to engage in ritual combat with a gloved arm that bears the odour of another male (Groves, pers. comm & pers.obs). Male white-throated monitors have been seen attempting to mate with dead females that still smell fresh (Lambiris 1966). Most monitors show very little external sexual dimorphism. This means that males and females look alike, so that often we can only determine their sex by internal examination. But the lizards recognise each other instantly by smell . In some areas they may be acquainted with the unique scents of many of their counterparts, and know which ones to avoid and which to follow. At least one author has reported a noticeable smell emanating from mating couples in the wild (Tasoulis 1983) and it is often possible to sniff out burrows that monitor lizards have slept in , even if the animal are no longer there. Several auth ors report that males follow the precise paths taken by rival males and females. A group of Bengal monitor lizards that escaped their captor in Florida hid themselves in the same tree that other escapees had used months before, although there were hundreds of other trees in the area (Auffenberg 1983a). Presumably the first monitors had marked the trees with long lasting chemical signals that the later escapees recognised and followed for safety. Studying olfactory behaviour in the wild presents e normous difficulties which have yet to be overcome. It is not yet clear by what mechanisms the lizard s release their pheromones. In some species scents seem to be left in faeces, which may be deposited strategically (Auffenberg 1981). Larger, dominant, animals probably leave faeces in more prominent places than their weaker counterparts. They may be used to warn off other monitors from strategic areas such as favourite basking places and strong burrows. More usually scent signals are produced in skin glands and rubbed onto the ground or onto strategic obje<.:ts such as trees or termite mounds. At present little is known about these glands and nothing about the c hemicals they produce. Monitor lizards spend a lot of time investigating each other with their tongues, particularly around the head, shoulders and the pelvic girdle, so it can be presumed that the glands are most common in these areas. Some species, such as mournful goannas. drag their taiJ base along the ground whiJe walking. This presumably leaves a trail of scent which "an be detected by other monitor lizards. Lace goannas leave scent signals by rubbing their vents on the ground or by wiping their heads on hard surfaces (Christie 1984 : Carter 1990). Most scent deposition is doubtless done in subtle ways that have so far eluded the eyes of researchers'. Having a distinctive smell can be dangerous however. because they reveal the animals' prese nce to larger predators. especially other monitor lizards. Presumably mechanisms exist which help di sguise strong smelling lizards from predators with a keen sense of smell. Juvenile Komodo dragons have been seen to di sguise their scent by rubbing themselves in
• A very important paper on this subject . which confirms many speculations. reached me just too late for inclu sion - Tsellarius & Menshikov (1994) 22
Insides & Outsides of Monitors unappetising bits of carrion (Auffenberg 1981). It is likely that monitor lizards are able to avoid an number of potential predators by recognising their scent. Experiments have shown that young captive born V.aLbigu/aris avoid foods that smell of cobra or viper, but happily take food smelling of harmless snakes. Furthermore the smell of venomous snakes initiates defensive behaviour, even if the lizards have never seen a snake in their lives (phillips & Albert 1992). The extent to which olfaction regulates the behaviour of monitor lizards, particularly in their social lives, is probably much underrated . Humans have an extremely poor sense of smell, which, of course, is why we know so little about it.
SIGHT. The eyes of monitor lizards are very well developed, and capable of seeing slight movement over distances of at least 50 metres. Footprints of perenties that suddenly break into a run and change direction suggest that they can see a moving human from over 200m away in open areas. Sight is important to monitors both for finding food and escaping from predators. Some monitors may lie in wait for tiny prey such as crickets and spring on them as they pass by. However they do not appear to be able to see still objects clearly and will sometimes ignore stationary people for hours at a time, but take flight at the first sign of movement The eyes are situated on the sides of the head and the eyeball cannot rotate in the socket. This means that the animals must move the entire head in order to look round . Unlike snakes, the eyes of lizards have lids, but they also possess a thin protective membrane which is moved horizontally across the eye with such speed it is rarely seen in life but often appears on photographs. I do not know whether monitor lizards are able to see in colour. Only one species, the Bengal monitor has been subjected to a visual discrimination test, involving two choices; light and dark . After two days they were scoring 85%, and after being left for 18 days they still managed to achieve the same score (Loop 1974). Monitor lizards appear to t.:ommunicate with each other by posture. They adopt highly stereotyped stances when approac.:hed by other lizards which seem to be indicative of their social status (Chapter 5). Some are said to be able to recognise individual people (Proctor 1929 for the Komodo dragon, Andres 1904 for the desert monitor), but whether this identification is based on visual or olfactory stimuli, or a combination of the two, has not been established. Monitors t.:annot see in the dark , and so almost all activity is restricted to the daylight hours. However individuals may occasionally move about on warm, moonlit nights (Auffenberg 19~ I), can forage at night around artificial lights (Fyfe 1979) and one species is reported to be most active at twilight (Christian 1977).
HEARING. The only sounds corrunonly made by monitor lizards are a loud hiss and the occasional sneeze, but some spiny-tailed monitors c.:an produce a rattling sound by striking the tail on a solid object, Bone (1920) record s a booming sound from a lace goanna and Ridley (1889) reported that water monitors were said to utter "the cry of the biawak", a loud, barking, laugh. Krishnan (1992) notes that Bengal monitors are reponed to snore at night and claimed that they issue a call not unlike that of a bird when frightened . The ears of monitor lizards are not particularly well developed, and whilst they can hear, they do not seem to rely upon them to look for food nor to communicate with each other. Many individuals do not react even to loud noises and it is often possible to creep up on basking monitor lizards from behind if they receive neither olfactory nor visual dues of your approach.
23
Little Book of Monitor Lizards
TOUCH. Monitor lizards respond to touch in a number of ways. They all scratch or bite their opponents and mates during fighting and courtship, sometimes to the extent that injuries occur. Physical contact provides a number of important stimuli in the social interaction of varanids, and may well trigger the release of some of the chemical signals discussed earlier. Similarly, stroking a monitor lizard's back usuaUy invokes a threat reaction, but "tame" monitors respond by lying perfectly still in a manner very reminiscent of their behaviour when confronted by a dominant lizard. Some lizards do not appear to find being stroked distressing. They react to being rubbed gently just behind the ear opening by closing their eyes and nodding their heads up and down in a manner not dissimilar to that of domestic cats. If a monitor is turned upside down, and its belly rubbed gently in a circular motion, they may become "hypnotised" and lie motionless, with eyes open for anything up to half an hour. A sudden movement or prod will bring them round and they immediately flick themselves over. This phenomenon has been observed in a number of lizard families.
SIZE. Body size in monitor lizards shows greater variation than in any other family of animals (Pianka I <)<)5) with adult animals weighing between 15g and 250,000g. The fanlliy includes both the largest living lizards and the largest lizards that have ever existed, yet about a third of the living species are dwarfs that seldom exceed 500g in weight. Such massive size disparity between species makes the group ideal model animals to study the effects of gigantism on ecology and physiology, but at present little of their potential in this field has been explored (McNab & Auffenberg 1<)76; Auffenberg 1981; King 1991; King & Green 1<)<)3, Case & Schwaner 19<)3, Pianka 1995). Obviously the size of an animal's body has a major bearing on the types of food it can eat and the habitats it can utilise, as is amply demonstrated by the changes in morphology that occur in the transition from juvenile monitor lizards to adults (see below). But for reptiles body size is perhaps particularly important from the point of view of water conservation and thermoregulation. The larger a monitor lizard is the slower its rates of water loss , heating and cooling are likely to be. Most big monitor lizards rely on massive numbers of much smaller animals to sustain them, which they collect by spending long hours foraging over wide areas. Large monitor lizards are not able to raise their body temperatures as quickly as those of a smaller size, but they can undertake prolonged activity in open sun that would rapidly fry their diminutive counterparts and because they loose heat less quickly they can remain active for longer in cooler conditions. Also their size deters many of the predators that would attack smaller lizards. With the fonnidable exception of mankind (and his dogs), there are very few records of mammals preying on large monitor lizards. Their usual enemies are big reptiles (particularly snakes and other monitor lizard s) and birds of prey. As adults, a number of large monitor lizards have no predators other than man and this, combined with their ability to withstand inclement temperatures, means that can wander about oblivious to at least some of the usual pressures of reptilian life. In almost all species that have been scrutinised male monitors attain greater lengths and weights than females. This difference is presumed to be due to the need for females to devote a great deal of energy to egg production. Possibly their smaUer size would make them more vulnerable to predation, but they also tend to be less active than males (spending less time moving around and covering smaller areas) and thus reduce their exposure to danger. This is
24
Insides & Outsides of Monitors of particular significance to the herpetoculturalist, because it means that females are less likely to be collected using most trapping methods and are therefore scarcer in captivity.
TEETH AND SKULL The shape and size of the skull and teeth determine the nature of the prey that can be manipulated and swallowed (Rieppel 1979). Like snakes, monitor lizards can swallow large prey items whole and they have similar adaptations as those of their limbless counterparts such as flexible joints between skull bones and an epiglottis that permits breathing even when the mouth is stuffed with food. Teeth are replaced at regular intervals throughout life (Edmund 1960, 1969) , but in captivity regeneration slows down and sometimes stops in very old specimens (Bell airs & Miles 1960). The shape and relative size of monitor lizard skulls varies greatly, as does the shape, size and number of teeth. The most comprehensive study of monitor lizards' skulls is by Mertens (I 942b). In the absence of first hand knowledge about a lizard's diet in the wild, a study of the dentition and skull can provide general clues about what its preferred prey might be. Species which feed on hard-shelled prey that require crushing before being swallowed tend to have thickened bones in the skull to which more massive jaw muscles can be attached . Lonnberg (1903) compared the skulls of Nile and water monitors of similar sizes and noted that the skull of the former weighed about three times more than that of the latter. The Nile monitor, the white-throated monitor and Gray's monitor all have large blunt teeth at the back of the jaws that, combined with the large jaw muscles, are capable of exerting enormous pressure on shelled animals. [n Bose's monitor the rear teeth appear to have the same function, but the front teeth are sharper, longer and more curved . Durneril's monitor, which may feed largely on crabs, has very different teeth which are few in number but very sharp and strong and are used to puncture the shells of their prey rather than crushing them. In most species the primary purpose of the teeth is to hold prey that are able to move quickly and are very anxious to escape. ln sectivorous species such as the rough-necked monitor have much more delicate jawbones equipped with large numbers of small, sharp teeth. The yellow monitor, whi ch often feeds on frogs, has similar numbers of teeth which are larger and straighter whil st the enigmatic Salvadori's monitor has very long conical-shaped teeth with which it is believed to capture birds and other fast moving vertebrates. But by far the most fearsome teeth in the family belong to the Komodo dragon . Said by tooth specialists to be more reminiscent of those of a shark or a Jurassic crocodile than any living lizard, the Komodo dragons' teeth bear hundreds of tiny serrations that enable the lizards to saw swallowable chunks from the carcasses of large animals by grasping the meat and rocking backwards and forwards. These teeth also allow them to disable enormous prey animals with a single bite by severing tendon s in the leg (Auffenberg 1981). Some other species, such as the lace goanna (Greer 1989) , also have serrated edges on their teeth, but no other monitor lizard appears to have teeth as well suited to slashing through flesh as those of the formidable dragon. In many species of monitor lizard diet c hanges with age , and this is reflect by changes in dentition. Very young Nile monitors have long sharp teeth housed in a relatively small skull. As the animals attain maturity the bones of the skull become much thicker and the sharp teeth give way to the broad, crushing teeth typical of the adults (references in Chapter 6). The very earliest members of the family appear to have had grooved teeth capable of transmitting venom (Chapter 2) No living monitor lizards have a poisonous bite but many
25
Little Book of Monitor Lizards species which regularly feed on carrion are hosts to particularly nasty bacteria in their mouth s. Swabs taken from the mouth s of wild Komodo dragons contain four types of wound-infecting bacteria, including "superbacteria" of the genus Proleus (A uffenberg 1981 ).
Above: Skulls of white-throated monitor (top) and Nile monitor
Opposite: Komodo dragon (lOp), water monitor, Gray's monitor (Ti m Garner)
26
SJOll li OIN ) 0 S:Jp lSl no
7f?
S:JPISlil
Little Book of Monitor Lizards Superbacteria are very resistant to natural defence me<.:hanisms and reproduce at phenomenal rates, soon wrning even a minor wound into a huge, festering sore. Thus even animals that initially es(;ape from the dutches of a dragon may shonly afterwards find themselves disabled by a virulent infe<.:tion that smells so strongly that all the monitor lizards in the vicinity are atuacted to it. Thankfully the animals loose these bacteria in captivity, and so it is presumed that they find their way into the lizards' mouths during meals of rotting flesh.
NOSTRILS At present little is known about the internal morphology of the nostrils (Auffenberg 1988) but the size and position of the nostril openings reflect the range of habitats and feeding te<.:hniques utilised by monitor lizards. The nostrils of species that spend a lot of time in water are often equipped with flaps of skin that prevent water entering whilst the animals are submerged (e.g. Dumeril's monitor, the mangrove monitor, the water monitor, Menens' monitor (Mertens 1942, Krebs 1979). In species such as the water monitor and the mangrove monitor the nares are situated towards the front of the snout, allowing the lizards to be able to keep almost all of the head below the water and still be able to breath. In Mertens' monitor, the openings are uniquely situated on the top of the snout rather in the fashion of crocodilians, so that the animals can breath even when the entire head is submerged. In other aquatic monitors (such as Dumeril's monitor and the Nile monitor) and in many ground dwelling species (such as the Bengal monitor and Bosc's monitor) the round openings are replaced with slits and situated closer to the eye than the tip of the snout. All of these lizards retrieve a lot of their food from below the ground. They use their remarkable sense of smell to dete<.:t prey and uncover it by pushing their snouts into the earth. The narrow slit-like opening prevents the entry of most of the debris that would otherwise (;ongest the nostrils. In some species this type of foraging behavioltr seems to be restricted to the older animals, and ont:e again we see examples of major change in the transition to adulthood. Both Bengal and Nile monitors have rounded nares as juvenile, which become narrower as the animals age. These species spend most of their time in the comparative safety of trees as juveniles and only seek food on the surface when they become larger. Bose's monitor, on the other hand, roots for prey with the snout virtually from birth and the shape of the openings does not change significantly with age. FEET & CLAWS Monitors use their feet to walk, dig, climb and occasionally tear apart food that is too large to swallow. Species that climb well tend to have flexible toes equipped with long, very thick, sharp, curved claws. The toes permit the claws to swivel and in some larger arboreal spe<.:ies are equipped with a locking me<.:hanism which enables them to support their entire weight with just one of the strong claws if needed. To descend they fall through trees with the claws held back wards, so that they drag thi'ough the vegetation and thus slow descent. In this way even very large monitor lizards are able to descend rapidly from the branches of tall trees. The massive claws can provide support both on thin branches and on vertical surfaces (Menens ILJ42, Landsmeer 1981, Auffenberg 1988). In captivity the illustrious tree t:focodile can t:limb vellical surfaces and remain there holding on with its hind feet alone, whilst the front legs reach out for a higher purchase. The front claws can also be used to tear holes in plaster walls and burrow through hard packed substrates. The delightful Australian rock goannas also have long curved daws and exceptionally long toes enabling them to climb high diffs and make rapid progress over slippery rocks. Unfortunately there are very few documented observations of these very fast and agile little gems in their natural habitats (Horn & Schurer I 971.{).
n
Little Book of Monitor Lizards
Monitor lizards which spend most of their time on the ground tend to have shorter toes and more slender, straighter claws than those of their climbing relatives (Mertens I 942a) . In some species these claws are very long and the front legs are extremely strong and well developed. The Bengal monitor, which is equally at home in tree s or on the ground, has longer toes equipped with short, powerful, strongly curved claws. They enable it to be dextrous enough to capture bats roosting in trees yet provide the mechanical strength to break open hardened tennite mounds. A number of monitor lizards (including Gould's goanna and the New Guinea tree monitors) are known to eviscerate larger prey using their foreclaws. The smaller monitors do not have to support such great weights and their claws tend to be much less dramatic. A number of smaller, agile species (such as the rock goannas and the New Guinea tree monitors) have curious groups of scales on the soles of their feet, which are sometimes reported to be sticky to the touch. The pads may be an aid to climbing or they may secrete chemicals of an odoriferous nature (Mitchell 1955; Horn & Schurer 197X; Greene 19~6).
TAIL The tail of a monitor lizard is truly a mUlti-purpose organ. The base can hold an enormous amount of fat which may be utilised when food is scarce. It is a very efficient weapon when used as a whip and can be deployed with great force. In aquatic monitors the tail is used to propel the animal through the water, in burrowing species it is often used to block the burrow entrance, whilst in arboreal species it aids balance and in several species it is able to grip like an extra limb. Most of the larger monitors can also use the tail as a prop to enable them to stand on their back feet, either to gain a better view of their surroundings or as part of a threat display. The length of the tail is often expressed as a percentage of the animal's body length measured from the tip of the snout to the vent, referred to as the SVL. So the total length (TL) of an adu It short-tailed goanna is about 20cm, made up of lOem each of head and body and tail - in other words "the tail is 100% of the SVL", whereas in a Glauert's goanna with 20cm of head and body and 50cm of tail "the tail is 250% of the SVL" . This terminology, though sounding ominously mathematical, is a convenient way of comparing the relative tail lengths of different species. Monitor lizards have tails which are between 80 and 250% as long as their bodies. The longest tails belong to the Australian rock monitors (Glauert's, «jngs' and the twilight goannas) and the mysterious tree crocodile of New Guinea. In the Australian lizards the long tail of the tail probably aids balance when leaping from rock to rock in pursuit of prey . It is often vividly banded or marked at the tip, suggesting that it could serve as a decoy against aerial predators. In tree crocodiles almost 200cm of tail provide a magnificent climbing aid , enabling these massive lizards to be as agile as monkeys in trees. The tail can be wrapped around branches for support and is strong enough to support the entire weight of the lizard during a rapid descent from a tree. The smaller New Guinea tree monitors are able to use their prehensile tail s in an even more precise way and may mate in mid air anchored to a branch only by their tails. Several of the small Australian monitor lizards have spiny scales on their tails. The spines act as armour plating, and are used in at least twO ways. When sheltering in a rock crevice the tail is used to wedge the lizard firmly in pOSition. When in a burrow it can be used to block the entrance, in both cases making the animal very difficult for a predator to dislodge. The spines are sharp and tough and deter many animals that would otherwise make a quick meal
30
Insides & Outsides of Monitors out of the diminutive lizards. When cornered the spiny tail becomes a spiked club, quite capable of drawing blood from a human hand. Some other large monitors (including the Bengal. Nile and Bosc's monitors) also use the thick tail base to block their burrow entrances. Instead of being covered in spiny scales, however, they are comparatively smooth, but very powerful, and capable of preventing many potential predators (such as snakes) from gaining enrry. Desert species and others that face long periods without food are able to store substantial amounts of fat in the tail base as well as within the alxlomen. Whether the fat stored in the tail is used in a different way to that of the alxlominal reserves is unknown. Even in animals a few months old the circumference of the tail base can vary by over 100% in animals of similar lengths. reflecting the different rates of feeding, and therefore growth, berween siblings (Bennett & Akonnor 1995). A number of large monitors are able to stand on their back legs alone for short periods of rime , fonning a tripod with the tail , allowing a much better view than is possible from a few centimetres above the ground, especially in tall vegetation. When monitors are threatened, either by predators or by their counterparts, they sometimes adopt this pose to make themselves appear larger or in preparation for ritual combat. Dwarf monitors appear to be unable to stand bipedally. Species that spend time in the water tend to have a long tail that is laterally compressed. Mertens' goanna provides the most exrreme example of this; its tail is very high with almost vertical, flat sides. The speeds attained by swimming monitor lizards have not been measured, but it is tikely that those with srrongly compressed tails would be capable of exerting much more thrust in the water than those with more rounded appendages. With a suitably shaped tail varanids are able to swim very efficiently and many species have been seen in the sea far from the nearest land. Because of their proficiency in water both water monitors and the mangrove monitor have spread over huge areas and inhabit numerous islands. Many monitors that rarely encounter water (e.g. Bosc's monitor, Caspian monitors and perenties) also have compressed tails, which they have presumably inherited from ancestors who lived more amphibious lives (Mertens I 942c). The tail also has an important use as a weapon of active defence. Stories of a blow from a monitor lizard's tail breaking peoples' bone are probably exaggerations but they are certainly capable of stunning many smaller animals. At least two species (rree crocodiles and Caspian monitors) are recorded as having specifically struck at the eyes of human aggressors with the tail tip (Murphy 1972, Bennett I 992a). A well aimed blow can have devastating results. Eidenmuller (1993) notes that sand goannas will use therr tails to flush out prey animals that have secreted themselves in inaccessible crevices.
COLOUR & PATTERN The pattern of adult monitors generally consists of a single ground colour with varying amounts of ocellations, spots and bands over the body surfaces. Usually it seems that the purpose of this arrangement is to make the animals difficult to see amongst rocks and vegetation. It is impossible to appreciate the camouflage of monitor lizards without seeing them in their natural environment. The amount of pattern tends to increase in wetter climates in species such as Bengal and desert monitors, with specimens from very dry areas often having no pattern at all.
31
Little Book of Monitor Lizards Newly hatched monitor lizards rarely resemble their parents. Youngsters of many species are almost unrecognisable because of their gaudy colouration. Dumeril's monitor provides the most extreme example. The purpose of their extraordinary appearance is unknown. A commonly held explanation is that bright colours serve as camouflage. Although the patterns of many adult monitors allow them to blend in with their surroundings and it is cenainly true that juvenile monitors are very rarely seen in the wild, but it is difficult to envisage a hatchling Dumeril's monitor being able to remain inconspicuous in any habitat. Another possibility is that the brighter colours and prominent markings of the young mimic the warning colouration of dangerous animals. Hatchling Dumeril's monitors show a strong resemblance to young spitting cobras (Bennett 1995) and the young of lace goannas, Nile monitors and water monitors are boldly banded with jet black and bright yellow. Juvenile water monitors are considered to be poisonous and I or venomous by people in some parts of their range. Whether this belief is shared by other potential predators would be best determined by experiment. Dramatic colouration differences between young and adult such as in Dumeril's monitor are also found in many territorial coral reef fishes such as the emperor angelfish, Pomacantlms imperatoI'. It is thought that in these animals the juveniles' colour protects them from aggression by adults, who do not recognise them as belonging to the same species. Thus for the early stages in life they are able to move about without regard for their elders' territories and without having to waste energy and risk injury or death in fights. Such an explanation seems unlikely in the case of monitor lizards, who are present at much lower densities than coral reef fishes and seem to recognise each other by smell rather than by sight. But in at least one species (the Bengal monitor) young lizards are known to remain with their siblings for some time after hatching. Perhaps the prominent markings of some juveniles make it easier for the fraternal group to recognise each other and keep close together. Some of the rock goannas start life with very brightly coloured tails, they may act as a decoy to aerial predators, as has previously been suggested for the light tail tips of adults. Hatchlings with red or orange colouration such as Dumeril's monitor and Rosenberg's goanna loose their bright colours completely within a few weeks but in general the patterns of the juveniles fade slowly with age. As the monitors grow larger they frequent different habitats. In many species the shift from an arboreal to a terrestrial existence is often accompanied by a reduction in pattern; bands break down into spots which disintegrate further as the animals grow, so that very old specimens may have virtually no pattern at all. Some aquatic species (Mertens' goanna and the Jobi monitor) have areas of bright colour on the throat which may serve as a warning signal when the animals inflate their throats in anger (Horn 1977). Other species (Gray's and the Yemen monitor) have prominent lighter markings on the snout that may serve as sexual stimuli (Auffenberg 19))8). Races of black monitor lizards are known from a number of species (e.g. water monitors, mournful goanna and New Guinea tree monitors). Often, but not always, they seem to be associated with coastal areas. The colour is likely to have a significant effect on their thennoregulatory behaviour, presumably allowing them to absorb heat faster than would be possible with a lighter coloured skin. In the Western Australian deserts the black form of the mournful goanna apparently tolerates body temperatures of over 45°C, several degrees higher than the temperature considered lethal for most species! To date there have been few studies conducted to look for differenl,;es in the thermoregulatory behaviour of melanistic races (Green & King IlJ7ll; King 19l)O).
32
4
The Lifestyles of Monitor Lizards
In order to be successful newly-hatched monitor lizards must evade predators and catch enough food to allow them to grow large enough to reproduce. On reaching sexual maturity females must invest massive amounts of energy in egg production and select a male who will make a good father for her offspring. Male monitors must search for females and assert their right to mate by fighting off rivals. Once copulation is achieved the female must find or build a nest site which will keep her eggs safe until they hatch. From egg to the grave the lizards' behaviour is under the strict constraints of their need to thennoregulate and conu'ol water loss, which may restrict their activity to less than half of the year. The lifestyles of most monitor lizards are virtuaUy unknown. The species that have been studied show that there are great variations in behaviour both between species and individuals. This is not surprising considering the incredible range of sizes found amongst monitor lizards and the wide variety of habitats that they are found in, including some of the driest deserts and wettest forests on Earth . Whilst some species, such as the Bengal monitor, are able to survive in many different habital~, others, such as Gray's monitor, are restricted to a very narrow range of environmenl~. The distribution of the species also varies tremendously. The desert monitor is found in virtuaUy all deserts from west Africa to east India, an area covering over 300,OOO,OOOm 2 whereas the total range of the Komodo dragon , which is found on only four small islands, is less than 2000km2. The entire known range of Teri's goanna amounts to less than IOOkm2. (Mertens 1942, Auffenberg 1981, Irwin 1994).
DEFENCE Monitor lizards are good to eat and aU but the largest specimens are subject to predation by reptiles, birds, marrunals and even fish. Their patterns provide them with a high degree of camouflage in their natural environmenl~ and their ability to "sniff out" potential predators allows them to avoid many confrontations. The literature suggests that snakes are among the most important predators of monitor lizards in many areas. The defence of juvenile monitor lizards rests with their secretive behaviour, congregational behaviour and cryptic or extraordinary colouration (see Chapter 3). Very few observations have been made on juvenile monitors in the wild, although they are often present at much higher densities than adull~, and this is testament to their ability to live undetected. Small monitor lizards escape predation by being extremely wary and dashing for cover at the fLfSI sign of trouble. Larger monitors have far fewer predators and tend to be more relaxed in the open . Often they freeze when they see people, rather than draw attention to themselves by running, and can remain motionless for long periods, keeping a very close watch on their adversary. If the observer is patient enough to remain stiU, the lizard may resume its activity, ignoring its audience. Many large monitor lizards do not appear to associate cars or bicycles with danger and some individuals have been described as fearless, inquisitive and even provocative. When running they sometimes attain great speeds and when in good form can easily outrun most people over 100 meu·es. There is little data available on the speeds attained by monitor lizards when running but they can certainly achieve sustainable speeds much higher than those of many other lizards (Lim 1958; Gleeson 1:1 at 1980; Auffenberg 1981; Velentic 1994). When running away from trouble monitor lizards head directly for a
33
Monitor Lizards of the World safe retreat; many select tight burrows or crevices in which to shelter from predators, often with several different exits (see below). Others seek safety in trees and yet others take refuge in water. The situation becomes very serious when the lizard has been detected by a predator and escape is impossible. At least two species, Bose's monitor and the rough-necked monitor, are reported to feign death with eyes wide open (Schmidt 1919; Horn & Petters 1982). However not one of over 250 Bosc's monitors that we have caught in Ghana has attempted to use this ruse, suggesting that the behaviour occurs only in certain populations or amongst certain age groups. Perhaps playing dead is used only in response to attack by certain predators, most would be as happy to eat a dead lizard as a living one. When attacked or threatened monitor lizards will almost always attempt to escape, but should confrontation become inevitable they defend themselves admirably. The threat displays of various species have been described and analysed e.g. V.mertensi (Murphy & Lamoreaux 1978) V.komodoellsis (Auffenberg 1981), V.olivaceus (Auffenberg 1988), V.wiseu.~ (Bels el at 1995). In general the lizards attempt to make themselves look as large as possible by standing upright on all four legs, flattening the back and inflating their lungs to the maximum extent. This effectively quadruples the volume of the body and makes even a very skinny specimen appear extremely robust. With one eye ftxed firmly upon its aggressor the lizards emit a malevolent hiss. Some large monitors may stand up on their hind legs at this stage and present a very intimidating sight, especially when swaying from side to side in the manner of a charmed snake. The effect is completed by distending the throat and opening the mouth to its widest extent, greatly exaggerating the size of the head. A monitor Lizard may remain in this posture (bipedal or quadrupedal) almost indeflnitely, the hiss being periodically interrupted whilst the lungs are reftiled. If the aggressor approaches closer the lizard may lunge with the mouth open and the tongue fully extended. These lunges are almost always bluff however and the lizard falls short of its target. The ortly physical contact the li zards will entertain with their enemies are sharp blows from the powerful tails. Large specimens are supposed to be able to knock people unconscious or break their Limbs but often the tail is used much more subtly and blows directed at particularly delicate parts of the anatomy. Only if an attempt is made to seize the animal will it resort to outright violence. Even small monitor lizards are very strong and fierce, so would-be predators must be careful that they do not end up worse off after an encounter with their prospective meal. Monitor lizards deliver a particularly savage bite and once they have seized something they may hold onto it like a bulldog. There is an old, but doubtless accurate, account of an Indian snake charmer who whose hand was seized by a Bengal monitor whilst he was trying to extricate it from its burrow. All attempts to free his fingers failed, and eventually his friends were forced to cut the jaws open with scissors (Mahendra 1930). By patiently hanging on to predators they may be able to exhaust them and then make a quick escape (Stevenson-Hamilton 1947). A number of monitor lizards have interesting relationships with cobras, where either animal may prey on the other (e.g. Bharatan 1971). It has been suggested that many monitor lizards are immune to the venom of cobras and vipers (Rjumin 1968; Root 1978) but in the absence of conclusive experiments this is .:ontested by many people.
MOVEMENT & SHELTER For most of the year monitor lizards move only to find food. When prey are abundant the lizards move much more than when it is in short supply. Male monitors reach the peak of their activity during the mating season (when they are seeking out females) whilst females are
34
Lifestyles of Monitors most active immediately afterwards as they searc h for nesting sites. At all times movement is resuicted by the need to thermoregulate and conseT'le water and, conversely, maintaining suitable body temperatures and reducing water lo ss are ac hieved largel y through movement (Chapter 3). Estimates of home range and daily distance rravelled have been reco rded for many species, but direct comparisons between them are impossible to make because of differences in the method s used and the seaso n, cl imat e, type of habitat, size of the lizards and durati o n of the stud y. Almost all studies suggest that for most of the year males are more active than females and that as a result males appear to be more common (e.g. Gaulke 1989b). Their hi gher activity levels are also respons ible for their larger food in takes and faster growth rates. Even within small populations so me individuals cover much greater distances than other of the same size and sex. The best data for movement pattern s in wild monitor lizard s comes from Auffenberg's (1981) stud y of th e Komodo dragon I, a very large lizaJ"d living on a small island. The results show that whilst some adult monitors may remain ill the same area for mo st of their lives and are very well acquainted with the loca l topography, others may be rra nsient and rarel y remain in one place for more than a co uple of days befo re moving on. Such differences between individuals may be commo n amongst monitor species. Vinually nothing is known of the movement patterns of juvenil e monitor lizard s. Many young Bosc's monitors remain in the same small fields for a month or more if food is plentiful and none have been obseT'led to rravel more than 150m in five weeks (Bennett & Akonnor 1995). Many monitor jjzards are exrremely adept at standing on their hind legs. This posture h a~ been obseT'led in many larger species, but not in any of th e dwarf monitors. A bipedal sta nce is adopted during ritu al combat or to gain a higher vantage point from which to sUNey the surroundings. Some spec ies also stand upright when thTeatened by tall predators, but this behaviour is limited mainly to some of the larger Au srralian goannas, partic ularl y Gould's goanna.
When monitor lizards are no t active they remain in shelters. Some species make use of rree hollow s, thic kets of vegetation, crevices in rock, termite mounds or bodies of water for shelter, but it is burrows that are of particular interest, for they provide the monitor with the opportunity to adapt the retreat to their own particular tastes. Unwillillg to expend any more energy than is absolutely necessary, monitors will steal the burrows of other animals and adapt them accordingly rat her than go to the rrouble of undertaking the entire consrruction themselves. Preferred sites are usually under rock, amongst large roots or in some other sheltered position. To us, a burrow is merely a hole in the ground but to a monitor lizard it is a haven to whic h rerreat may be made from the everyday pressures of reptilian life. As well as providing shelter from exrremes of heat and co ld and acting as a humidity rrap, the humbl e burrow provides a refuge during periods of inactivity (w hen digesting large meals, during inclement weather or just out of sheer laziness), a hideaway from predators, a rrap for prey, a cozy lov enest during the breeding season and, if required, can be adapted to make a nest for eggs. Monitor burrows vary greatly in size and shape and descriptions of the burrow s of many species have been published (references in Chapter 6). The deepest2 are those of desert monitors, such as th e Caspian monitor that has to endure winter temperatUJ"es as low as 30°C. Such burrow s are more than a metre deep and can be many merres long. They are
I See also Phillips (i n press) for a detailed study of moveme nt in th e white-thToated monitor 2But see also Traeholt (in press a )
35
Monitor Lizards of the World probably constructed by the combined effort of many generations of monitors (Bennett 1992b). Storr's goannas in tropical Australia are said to dig and cohabit shallow networks of burrows whilst several species may shelter in shallow bWTOws that provide an eme rgency exit through the terminus if the enrrance is blocked. (Bustard 1970). Patterns of burrow use by Komodo dragons, Bengal monitors and water monitors are particularly well do<.:umented (Auffenberg 1981. 1983a; Traeholt in press a). Monitor lizards rarely use the same burrow twice in as many nights and because they are not territorial a good burrow may be used by many different lizard s in the course of a year . Generally the burrows are used by one monitor at a time, although there are several records of a pair (presumably a male and female) found huddled together in the same hole. Other animals may also enter the burrow for shelter and stand a good chance of being gobbled up by the landlord. Whittaker (1970) reports finding a co bra and a monitor lizard sharing the same bUlTOW without adversity.
FEEDING With the exce ption of the fruit-eating Gray's monitor, all monitor lizards are totaUy carnivorous (Auffenberg 1988) . With the exception of the Komodo dragon , monitor lizards only catch animals that are smaller than themselves (Auffenberg 1981). Although monitor lizards are capable of overpowering and swallowing prey of around a third of their own body weight , most feed largely on much smaller animals. Several big monitor lizards are known to consume large numbers of tiny invertebrates. particularly orthopterans and beetles, whilst other species of a sinnilar size show a tendency to feed mainly on vertebrates. Similar differences in prey preference exist between dwarf monitors but in general the diets of all monitor lizards include a variety of animals of different sizes and they are often thought of as generalised feeders that will consume anything they are able to catch. This is an oversimplification however. [n order to grow and reproduce monitor lizards must obtain more energy from their food than they use to catch it. Most food items will be laclcing in some essential nutrients and so it may be necessary for the lizards to obtain a varied diet. [n different habitats and at different times of the year the number and types of prey available to the lizards fluctuate and so feeding strategies must change accordingly. Lizards find food either by actively searching for it or by concealing themselves and ambushing prey as they pass. The eviden<.:e for this "sit and wait" behaviour is largely anecdotal because direct observations are very difficult to make (Pianka 1968, Horn & Schurer J978, Auffenberg 1981). Foraging behaviour is much better documented from observations of wild and captive animals and from interpretation of footprints and other mark s left in soft ground, but data on the precise foraging movements of monitor lizards are difficult to obtain in the wild (Thompson 1992, Tsellarius & Cherlin 1991) and surprisingly few detailed observations from captivity have been published (Auffenberg I 983c, Traeholt 1993; Kaufman el at 1994). Many species systematically visit areas likely to contain prey (cow pats, water holes, trees. piles of leaf litter, tennite mounds, burrow s. shorelines etc.), often travelling over Ikm per day and moving directly from one foraging area to another. Whilst walking they continually taste the air and watch for any movement [f suitable animals are encountered in the open the lizards may rely on their superior strength and stannina to outrun and overpower them. When they detect an intere sting smell the rate of tongue flicking increases and the path taken becomes more convoluted and concentrated. When the source of the smell has been determined the claws and snout (and occasionally the tail) are used to uncover the prey, which are pounced upon as soon as they move. These observations srrongly suggest that monitor lizards find a
36
Lifestyles of Monitors lot of their food by sniffing it out, but rely on eyesight to locate the prey with enough precision to ensure it does not escape. Whenever possible monitor lizards swallow their prey whole. Small animals are swallowed alive, larger prey are killed flfst to make the process easier. Prey is usually seized by the head or neck and either shaken violently or slammed against a hard surface before being swallowed head first. The shells of snails and crabs are crushed, pierced or removed, whilst animals with long legs may have the offending appendages ripped or levered off before being consumed. The tongue has lost the ability to manipulate food in the mouth (although it may be used by some species to lick up small insects (Mertens 1942a», and "inertial feeding" is used to get food into the stomach (Smith 1986). The monitor holds the food in its jaws and momentarily lets go, whilst at the same time jerking the head backwards and forwards and then grasping the food again, so that it ends up further inside the mouth. This is repeated until most of the prey is inside and then the head and neck are raised and the food falls further down the throat. It is forced into the stomach either by the lizard flexing its neck to the left and right or by muscular contractions from within. Animals that are too large to be manipulated with inertia are crammed into the mouth by employing a rock or the ground as a lever. With the aid of these methods food of a swprisingly large size or inconvenient shape (such as thorny lizards and large tortoises) can be swallowed intact. Many monitor lizards will feed from the carcasses of dead animals, including human corpses. Some will eat flesh that is in a very advanced state of decay but most prefer fresh carrion. Monitors waste very little of their food compared to mammalian carnivores such as cats (Auffenberg 1981) and will even eat bones with no meat on them. Many are able to consume almost half of their own body weight in food and their very efficient digestive systems enable them to break down even the largest meals within a week if body temperatures are high. Gorged monitor lizards cannot run very fast and so it is important that the digestive pause be as short as possible. Only feathers, claws, fur, scales, fragments of bone and chitinous shells pass through the lizards undigested. This material is usually expelled in faeces but may sometimes be regurgitated as gastric pellets (Petzold 1967) Much has been made of the Komodo dragons' habit of preying on buffalo weighing up to 15 times as much as themselves (Auffenberg 1981). Amongst other reptiles only the crocodiles kill larger animals, and they do it from the relative safety of water. The evidence for Komodo dragons catching massive prey is largely anecdotal, but some certainly attack animals five times heavier than themselves. However even if such attacks are successful they are Wllikely to be able to consume much more than 10% of the prey themselves. Why, then, do they attack such dangerous animals? Mammalian predators that hunt bigger animals tend to do so either as a group or in order to feed a family. Monitor lizards have no such social spirit. The partly eaten prey attracts many other dragons to the site in search of a free meal and such congregations provide the opportunity to meet potential mates. It seems possible therefore that a few very large and experienced males risk catching huge prey in order to attract females, who, if they are wise, will consider the great strength and skill needed to kill such animals to be admirable characteristics. The successful hunter will have the opportunity to assert his dominance over the other males dragons, very few of who would be capable of such a feat themselves. If this were the case we would expect that only males would attack very large animals. UnfortWlately there is no evidence for this.
37
Lifesty les of Monitors
,;/ ~ ~." ;t:....
_.
,
/
., I
I
\
".
.,
'.
\
.~~~ . <''::;.~''''i " "' (
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( ....,,:;;;r;i<;'If 1.: ''1. i': \' \..
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,
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t
Opposite: Bipedal ritual combat in a large monitor (M'], Bennen after Tsellarius 1994). Above: Ritual combat in a dwarf monitor (M .J ,Bennen after Carpenter el at 1976),
39
Monitor Lizards of the World
SOCIAL BEHAVIOUR Monitor lizards are not usually sociable animals. Congregations of monitor lizards have been reponed amongst juveniles, around carrion and on riverbanks but most are solitary creatures that shun company except during the breeding season. They are not territorial in any strict sense and the activity areas of many animals may overlap. However most have activity ranges that are large enough to make accidental encounters unlilcely, The lizards are certainly able to detect the presence of other monitors by the smells they leave behind them. Quite often, when two monitor lizards meet one will attempt to eat the other. They are well equipped to deliver savage bites and grievous scratches and so every encounter is potentially dangerous. When face to face with each , other monitor lizards engage in a series of distinctive behaviours, so me of wh.ich are h.ighly ritualised (e.g. Auffenberg 1978, Daltry 1991). All involve a series of visual and probably scent oriented cues and they playa very important role in preventing the lizards' social occasions from degenerating into a cannibalistic orgy. Rirualised fights have been recorded for many species of monitor lizard (e.g. Ali 1944, Deraniyagala 1958a, Murphy & Mitchell 1974, Carpenter el al 1976, Auffenberg 198Ia&b, 1988, Tsellarius 1994 and particularly Hom 1985 & Hom el al 1994). The most dramatic are those of the larger species in wh.ich the animals stand bipedally, gripping their opponents around the shoulders and attempt to wrestle each other to the ground. In dwarf monitors and some larger species the wrestling matches only occur in a horizontal position, with the lizards grasping each other with all four legs and sometimes supporting themselves only with their head s and tails. Again the object is to overpower and get on top of the opponent. In all cases these ritualised fights allow the lizards to test their strength against each other without incurring serious injuries, particularly bites. Only rarely does one lizard break the rules and tear the other to pieces. Success in combat seems to be determined largely by strength and the winners tend to be the heavier animals, at least in bipedal contests. The fights are often presumed to occur only between males but there is evidence that they are practised by both sexes (Gaulke 1992a, Hom el al 1994). However males appear to engage in engage in ritual combat more often, as is evidenced by the large numbers of scars on the backs of old specimens. In the wild the fights are often observed to occur around carrion and are most common during the breeding season. Once dominance has been established the losers may avoid having to fight rematches by displaying appeasing behaviours when they encounter the dominant animal (Auffenberg 1981 , Daltry 1991). It is presumed that animals which habitually win in bouts of combat have access to better resources (food, she lter, basking sites, nest si tes) than the losers, and that amongst males, the dominant animals would be more likely to be successful with female s, although this is not always the case (Carter 1990).
REPRODUCTION. All monitors reproduce by laying eggs and usually viable eggs are produced only within two months of mating. Observations in captivity (Card 1993, Eidenmuller 1993) suggest that in some cases sperm storage of up to three months is possible. In many species mating and egglaying occurs only during a few month s of the year but in some tropica l species the breeding season is extended and may continue throughout the year. Very few studies of free living monitors have been able to gather much infonnation about reproduction but a great deal of data is being accumulated for captives (see Hom & Visser 1990, 1991 for reviews). Plior to mating the female must expend a great deal of energy in the production of eggs. The male uses a comparatively minuscule amount of e nergy making spenn. For this reason females are usually less active than males, grow at slower rates and achieve smaller s izes. The 40
Lifestyles of Monitors number and size of the eggs produced varies enormously between species. Some produce clutches of eggs that weigh almost half of their body weight. The eggs take up so much space in the body cavity that the female may be unable to feed whilst heavily gravid. Clutch size and relative mass vary greatly between species. Some large monitors lay comparatively light clutches whilst some small species produce what appears to be an impossibly huge clutch. The most prolific species are the African white-throated, Nile, and Bosc's monitors, all of which lay large numbers of eggs which hatch quickly into small offspring, each with very little chance of survival to adulthood. Other large monitors produce small clutches of eggs that may require longer incubation and hatch into much larger offspring. Even among dwarf monitors clutch size varies by several magnitudes. Females may accumulate the energy used for egg production as fat whilst food is abundant and make the eggs during periods of relative inactivity. In other species egg production does not appear to rely on large fat reserves. Whether a monitor can make a full clutch of eggs depends on the amount of energy she can afford to invest in them. Observations in captivity have shown that many monitor lizards are capable of producing more than one clutch of eggs per year if they have unlimited food resources. In most cases two clutches of eggs are produced in quick succession but some monitors may produce a clutch of eggs every three months. Some can produce their own body weight of eggs in a year, but it is doubtful that free-living individuals ever have life so good. The methods currently used to investigate the reproductive biology of monitor lizards in the wild require that the animals be killed and so there is no evidence that multiple clutching occurs in the wild, but it certainly occurs wherever suitable food and climate exist. Having produced a clutch of eggs at great expense, the female needs some good quality sperm to fertilise them. She indicates her sexual receptiveness by releasing scent signals which may be detected by a large number of males. But the males, literally bursting with sperm, flfSt seek out other males and engage in the bizarre contests of strength which seem to detennine their likelihood of achieving successful copulation. The amount of energy female monitor lizards must expend to produce young with a good chance of survival forces them to live relatively sedentary lives during at least part of the year. It is clearly in her interests to have them fathered by the most desirable male available. From her point of view a desirable mate is a big, strong one. Monitor lizards, as we have seen, are very well equipped for killing other animals and often practise cannibalism. Therefore in their social interactions with other monitors they must adopt very different behaviours than those employed in the quest for food . The riTUal combat practised by monitor lizards permits a hierarchy to be established without continual fighting. Similarly courtship in monitor lizards, although less riTUalised, reduces the chances of serious injury or death when investigating possible mates. Detailed accounts of courtship and mating can be found in Auffenberg (198Ia&b, 1988), Moehn (1984), Carter (1990), and Green & King (1993). In some species the female tends to be the dominant partner and only males strong enough to completely irrunobilise her are able to achieve copulation. In some species the act of love is performed very gently, but in others it is accompanied by a great deal of biting and scratching. Some accounts of mating could be interpreted as rape. Actual copulation is very short in some species and protracted in others, with mating occurring over several days. Male monitors are endowed with two penis-like structures which allow them to mate on either side of the female. They may use them alternately or prefer one to the exclusion of the other. The sUlfaces of the hemipenes are amazingly convoluted and they vary so much 41
PllOM ;)41 JO Spll!Z'1
lOllUOW
Lifesty les of Monitors
Opposite: Courtship in water monitors (Indraneil Das)
Above: Bengal monitor excavating a termite mound (lndraneil Das)
43
Monitor Lizard s of the World between species that they are used as a taxonomic tool (Branch 1982; Bohme 1988). Females also have twinned appendages that are partly eversible and may represent glands which produce sexual pheromones·. Most records of counship and copulation in monitor lizards come from captivity, where animals have less opponunity to escape from each other and serious injuries are not W1common. Nevenheless mating is a dangerous activity and Auffenberg (1981) has suggested that pair bonding may occur between some male and female Komodo dragons. This does not imply any sort of monogamous relationship (as incorrectly stated by Seibert (1994)), but rather that acquainted animals mate with each other more than with other individuals and thus reduce the danger of sustaining injuries from an incompatible liaison. In bonded pairs mating is accompanied by much less preliminary courtship than in unacquainted animals and some counship behaviour may occur between the pair at times of year other than the mating season. The extent to which pair bonding exists in other monitor species is unknown, but reports of captive breeding indicate that it may be widespread. Female monitors have limited ability to store sperm and so eggs are always laid within a few weeks of mating. The eggs are covered with a flexible, leathery shell (Zwineberg (1972) fancifully portrayed monitors emerging from chicken eggs) which are very prone to desiccation in dry conditions. Therefore they must be deposited in a nest which provides the heat and humidity necessary for them to develop into fully-formed lizards. Monitor lizard nests are very carefully concealed and there are very few records of nests discovered in the wild (Tsselarius & Menshikov 1995 provide a detailed exception). In all species studied female monitors reach the peak of their activity as they begin to search for suitable nesting sites. They may have to fight against other females to gain access to good areas. Nests tend to be si tuated in an elevated position, presumably to reduce the danger of flooding. Despite many claims in the literature no monitor lizard eggs have been found in tree hollows. Many species deposit their eggs in chambers at the ends of burrows of varying depths which are always refilled to some extent. A number of test, or decoy holes may be dug nearby. Females may actively defend their nests for a few days after egg laying, but this behaviour does not persist for long before the weak and hungry lizard goes in search of food . For many species tennite mounds provide the perfect incubator. The female simply locates an active mound , tears a hole in it and deposits her eggs. For reasons not understood the termites do not destroy the eggs but quickly repair the damage done by the lizard, thus sealing the eggs inside. Active tennite mounds are maintained at almost constant temperatures and are much more humid than the surrounding air. Furthermore the nest is well protected from predators and as long as the mound is not abandoned by the termites the eggs are safe. Surprisingly many young monitors born in termite mounds do not feed on their guardians (Carter & King. pers.comm.). The construction of some tem1ite mounds allows the newly hatched lizards to escape via ventilation shafts that lead to the outside. but in other mounds they may be entombed. lacking the strength to break through the tough outer walls. The question of how these lizards escape from the mound has not been solved. Several times it has been suggested that the mother
• These structures are much more exciting (han I had anticipated -see Zeigler & Bohme ( 1995 ).
44 -j
Monitor Lizards of the World returns to the nest when incubation is completed and digs out the youngsters (Cogger 1967; Boonratana 19RH: Ehmann ct al 1991). Many people remain unconvinced that the monitor lizard is (;apaole of remembering her nesting site and returning there at the correct time and unfortunately the results of field work investigating this phenomenon are not available (Carter Il)H9: Boylan 1995). A television documentary which purported to show the release of hat(;hlings from a termite mound by their mother used broad artistic license (Marven I ':1':10). My own opinion is that a (;omplete lack of parental care in monitor lizards would be surpri sing, espet:ially in view of their apparently analogous evolution with snakes, many of whom protect their eggs throughout incubation. As well as utilising active termitaria many monitor lizards deposit eggs in mounds that are no longer inhabited by termites. An important distinction can be drawn between these behaviours. Although any monitor can lay its eggs in an abandoned mound the ability to use active mound may depend on special (probably chemical) adaptations that prevent the termites from recognising the eggs as foreign and destroying them. If this is the case it would suggest that the lizards are only able to make use of the mounds of certain species of termite. At present there is not enough data to confirm or refute this. Speed of incubation is determined largely by temperature and in the wild some eggs may take almost a year to hatch. Incubation times in captivity exist for most species but virtually none exist for eggs laid in the wild and the only published data on the conditions experienced in natural nests is provided by Ehmann et a/ 1991. Oearly it is beneficial if the young lizards emerge at a time of year when their is plenty of food available, but this is not always the case. The eggs of the desert monitor, for example. may hatch shortly before the onset of winter and the youngsters remain together in the nest until the following spring. In some species the development of the embryos may be completely halted during very cold weather and in others development may be completed months before the eggs hatch. Most hatch (and all emerge) from the nest at a time when insect abundance is high. They lead very secretive lives, remaining mainly in shady. humid microhabitats and feeding voraciously. Mortality is very high in the first year of life and the small amount of data available suggests that many eggs may fail to hatch at all (Ehmann et al 1991; Phillips & Packard 1994; Tsellarius & Cherlin 1':1':15) .
46
5
Monitor Lizards and Man
Our relationship with monitor lizards stretches back over 90,000,000 years. For almost all of this time they have been the predators and we the prey. The flTst documented cases of predation on monitor lizards by hwnans date back about 40,000 years (King 1962). Today mankind's relationship with the monitors is a complex one. They are undoubtedly the most important of the lizards to the human race
THE MONITOR IN FOLKLORE AND ART.
Monitors are often said to have provided the inspiration for mythological dragons, but many
other animals have equally strong claims. Marco Polo's description of the Great Serpents of
Karazan could eas.ily refer to a Komodo dragon:
"Here are great serpents ten paces in length and ten spans the girth of the body. At the forepart near the head they have two shon legs, each having three claws like those of a tiger, with eyes larger than a four-penny loaf and very glaring. The jaws are wide enough to swallow a man, the teeth are large and sharp and their whole appearance is so fonnidable that neither man nor any other animal can approach them without terror." The earliest known depictions of monitor lizards come from cave paintings near Bhopal made about I0,000 years ago (Das 1989). They frequently appear in ancient and modern Australian art, but they are conspicuously absent from the an of the ancient Egyptian civilisations. According to Rose (1962) monitor lizards were often depicted and embalmed by the ancient Egyptians. However the Egyptians did not begin to mummify reptiles until the later dynasties (about 4,000 years ago) when they were associated with the sun god Atum, and a search of the mummified reptiles in the British and Cairo Museums has not revealed a single sptx:imen of monitor lizard (Bennett & Monnor ms). The most likely reason that the varanids were excluded from the afterlife is that they prey on the eggs and young of crocodiles, which, although despised, were considered highly sacred by the ancient Egyptians. Folklore is rich in superstitions and anecdotes concerning monitor lizards. In some places they are despised or even feared, but many cultures appreciate the lizards and some hold them in great reverence. Stories that monitor lizards are venomous or even poisonous abound in the early literature. The siliva is considered poisonous in Bengal and in pans of Borneo they are always cooked with ginger as a precaution, because if a poisonous individual has been selected for the pot the mixture will tum black (Saha 1983; Auffenberg 1982). Mason & Theobald (in Gaddow 190 I) claimed that Burmese Karens ate monitor lizards, but discarded the heads btx:ause they considered them poisonous. The secretive rough-necked monitor was believed have so venom so strong it could kill an elephant (Lekagul 1969). In Sri Lanka water monitors are often considered unpalatable whilst Bengal monitors are eaten with relish (Deraniyagala I<}S3). However treading on the faeces of the lizards rrtay cause your feet to erupt with sores (de Silva, pers.corrnn.). The lizards' ability to prey on venomous snakes is recognised in many cultures and in Australia, Egypt and Algeria their immunity is often attributed to their habit of seeking out medicinal plants after rtx:eiving a bite (Reed 1987 , Anderson 1898, Marnir. pers comm.).
47
Little Book of Monitor Lizards Monitors can bestow bad luck on people in a number of ways. In Borneo they are sometimes depicted on the shields of warriors in order to strike dread into the hearts of opponents. If one crosses the path of an advancing army mutiny may result unless the battle is postponed. If one is seen at a wedding the union is presumed doomed from the beginning (Auffenberg I<JX2). In parts of Pakistan it was considered essential to keep your mouth tightly closed in the presence of a monitor lizard; one glimpse of the teeth and the reptiles' spirit could infect your soul (Minton 190/i). If a monitor ran between your legs in Khazakstan your chance of having children in the future was rated as zero (Nickolskii 1915). In parts of Thailand some people dare not even pronounce the name of the monitor lizards, whilst others use it as a term of abuse (Nutphand undated). Further south, when the moon is full, some unfortunate people break out in scales and develop a long forked tongue. These "weremonitors" prowl about searching not for beetles and caterpillars, but for warm human flesh (Auffenberg 19X2). Many cultures distinguish clearly between good monitor lizards and bad ones. Around the Garo Hills in India water monitors with clouded markings were considered evil creatures that dragged men underwater and drained them of blood. Those with bright patterns (known as Aringgas) were supposed to be friendly and are depicted on the doors of Bachelors' houses belonging to the Atong and Ganching tribes. Another Garo clan, the Dawa, have the following story about their founder. Once upon a time when Dawa was a young man, he came across a baby Aringga which was feeding on melon leaves in one of the village fields. He caught it and put it in a cage, feeding it with fruit. Every day the baby monitors' parents would come and visit their imprisoned child, and when Dawa saw the two enormous Aringgas he became terrified in case they decided to take revenge on him or his people while they were crossing the river. So he dressed the youngster in a yellow coat, put earrings in its ears, released it and promised the parents that he would never catch monitors again, and asked them in return not to eat any of his clan if they identified themselves before they entered the water. The young Aringga became Dawa's friend, and when it grew up used to carry him across the river on its back. To this day Garos never kill Aringgas, and always callout "I am a son of Dawa" before entering the river. If one is accidentally caught it is given some earrings by way of an apology and released (Parry 1932). According to legend, bark canoes were flTst invented by Mertens' goannas, who had to learn how to climb in order to get the raw materials for their crafts (McConnel 1957). The industrious and ingenious goannas became lazy when they arrived in southern Australia. They abandoned farming and took to catching small defenceless animals, eventually resorting to stealing food from porcupines after stupefying them with honey (Reed 1987). In Malaya it was believed that water monitors hatched from crocodile eggs, but stayed on the land whilst some of their brothers and sisters made straight for the water and thus became true crocodiles (Ridley 1899). Strangely a similar belief persisted in Egypt, where the Nile monitor was believed to be the first stage in the life cycle of the crocodile, and Herodotus (circa. 450 BC in Anderson 111911) described the desert monitors he saw in Libya as land crocodiles.
4)1
Monitors & Mankind
USES OF MONITOR LIZARDS BY MAN
Mankind uses monitor lizards in a number of ways; for food, as pest controllers and to make
drugs and leather. In some parts of the world they are of enormous economic importance,
but in a few places they are considered a menace and efforts made to obliterate them.
The diets of many monitor lizards make them ideal pest controllers, and their use as such is undoubtedly their most valuable property. They eat crocodile eggs and venomous snakes as well as huge amounts of crop-damaging crabs, snails, beetles and orthopterans. In many parts of Africa and Asia they are encouraged to inhabit paddy fields, coconut groves and other farmland to reduce crop damage (e.g. Deraniyagala 1931). Rosenberg's goanna may have been introduced to many islands off South Australia to reduce the numbers of venomous snakes (Chapter 5) and the World Health Organisation considered introducing the mangrove monitor to rat-infested islands in the Pacific until its decided preference for crabs became apparent (Uchida 1967). The few studies conducted on monitor lizards living in agricultural areas have all indicated that their diets consist largely of animals that are injurious to crops (Auffenberg et al 1991, Traeholt 1993, Bennett & Akonnor 1995) and in many areas their habit of consuming carrion is approved of. Where monitor lizards are not persecuted they will live close to (or even within) human settlements, foraging around rubbish dumps and feeding on all manner of debris. They are a common sight around some of the largest cities in Africa, Asia and Australia and are presumably tolerated because they help to reduce the amount of food for rats, flies and other urban pests. The juicy flesh of monitor lizards has long been appreciated. It is rich in fat and can be roasted, griUed, smoked stewed, curried or fried. If cooked carefully, it is tender and not in the least stringy or tough. The choice cuts are the liver, the base of the tail and the eggs. Cochran (1930) reports that the eggs of water monitors were considered suitable for presentation to the King of Thailand. Followers of Islam in Asia will not eat monitor lizards, but many devout Muslims in West Africa consider them a great delicacy. In some parts of the Philippine Islands water monitors are a major food item and in many parts of the world they are used to augment pitifuUy small protein intakes. Their use as food throughout Africa, Asia and Australia appears to be widespread (e.g. Irvine 1969). The mangrove monitor has been introduced to many islands in the Pacific within living memory, possibly as a food source (Chapter 6). A bewildering array of tonics, medicines and potions are made from various parts of the monitor lizards' anatomies (e.g. Gaddow 190 I, Auffenberg 1982, Das 1989 and references cited therein). The fat is used to treat deteriorating eyesight and for a variety of other ailments (particularly arthritis, rheumatism, piles and muscular pains). It is also used as a sexual lubricant (Saxena 1993). Dried gall bladders are particularly therapeutic, curing heart problems, impotency and liver failure as weU as a number of more serious complaints. In North Africa dried heads of monitor lizards are sold to be pulverised and used for the treatment of various external and internal afflictions (Linley, pers.comm.). Amnesiacs in Sri Lanka sometimes prepare a meal of monitor lizard tongues, which is said to restore the memory to its full capacity (de Silva, pers.comm). Krishnan (1992) reports that a man who had sustained a serious thigh wound as the result of an encounter with a wild boar was treated by his friends in the following manner: Thin slices of fresh, Bengal monitor flesh were inserted into the deep wound , wh ich wa s then bandaged up . The man later claimed that the
49
Little Book of Monitor Lizarns wounn han healen l:ompletely within ten nays ann exhibited a "surprisingly small" scar. As far as I am aware none of the monitors' therapeutic properties have yet been subjected to serious suutiny. In Sri Lanka it was also believed that a mixture of water monitor fat and flesh and human bloon ann hair makes a very strong poison when boiled, and that a drop is sufficient to l:ause the instant neath of an enemy (Auffenberg 19R2). Water monitors were also said to ne instrumental in the preparation of the Singalese assassins' most favoured poison, kabara tel. The raw ingredients (fresh snake venom, arsenic and various herbs) were mixed with water in a human skull ann placed on a fire. at three corners of which bound water monitors were strategically placed ann beaten. so that their hisses would hasten the boiling process ann adn to the strength of the concoction. The froth from the lizards' lips was added at the last minute. <Jnd when an oily scum rose to the surface the nreadful potion was complete (Morris ill Gaddow I <)() I). An:orning to Das (19RR). killing monitor lizards with rakes is a form of sport in parts of northeastern India. Similarly. children in parts of the Kara-Khum desert take great delight in seeking out Caspian monitors and bludgeoning them to death. Because the lizards are believed to be venomous, participation and success in this sport is considered to be an act of gre<Jt bravery (pers. obs.). The ingenious ann renown Mararathi warrior Karna Singh breached the walls of the Fort of Kelna by tying a rope to a monitor lizard, allowing it to scale the wall and following it up when it han sel:ured itself in a tight crevice. Thereafter his tribe were known as Ghorpade (after the Marathi name for the Bengal monitor. ghorpad) and every soldier in the army was trained in their use (Ramakrishna 19R3). Less heroic individuals used the lizards to climb the walls of houses they were burgling (Robinson in Gaddow 1901). A number of cultures were said to allow monitor lizards to feed on their deceased relatives and thus eliminated the need to dispose of corpses by burying or burning them. In the Mergui Archipelago corpses were left on exposed platforms in the forest whilst on Bali the bodies were covered with wicker baskets that kept dogs and monkeys out and allowed the lizards to feed in peace (Anderson 1889, Auffenberg 1982). Such free and nutritious meals attracted large numbers of water monitors. Anderson reports that up to 15 specimens were seen "engaged in a ghastly meal of this kind". By far the most conspicuous use of monitor lizards is for their skins. Traditionally used for drumheads and shields, monitor skins are in great demand in the richer parts of the world to make watchstraps, shoes, wallets, handbags and other leather goods. The exquisite patterns of the lizards combined with the durability of their hides make them the most popular family of lizards in the skin trade. Most are caught in the poorer countries of central Africa and South East Asia and are sold in Europe, North America and Japan. As far as I am aware there is no demand for monitor lizard meat in Europe, nor are the gall bladders widely available, so the demand for the animals comes only from the fashion markel The numbers of animals involved in the trade is vast and the reported numbers may represent only a small proportion of the actual trade. Until 1975 there was no international attempt to monitor the number of lizard skins shipped from country to country. but there is no doubt that in many areas a flourishing export trade has existed for well over a hundred years. Mertens (1942a) suggested that the Second World War was beneficial to monitor lizards, by providing them with some respite from intensive exploitation.
50
Monitors & Mankind In IlI73-74 Ihe Bangladeshi Government estimated Ihal exports of lizard skin were worth more than US$I.300.000 (Gilmour 1984). Reponed trade in lizards skins from India bel ween IY(,4 and IY73 was over 2.5 million kg. valued at aimosl 15 million rupees (Anon IY7X) However trade reported to CITES during 1975 amounled 10 only 51.239 skins. of which 3X,47X originated in the Indian subcontinent. Minimum net trade in monilor lizard skins from IY75- 19Y3 are shown below. The significant rise in numbers bel ween Ihe lale 1lJ70's and Ihe early XO's is more likely to be a reflection of the increasing efficiency of Ihe reponing syslem rather than a true indication of a rise in demand . Figures for 1993 are im;omplelc. World Trade In Monitor Skins 1976-1993 3.0
S K I N S
B
2.0
I
III
I L L I
o N S )
, .S
' .0
:11 •• I I I I I 1,1 1.1.1 I I I _,_
,~,=,m~nl~I~I~,m,~,m,mlm'~'~I~'m,m'm
WORLDWIDE TRADE IN LIVE MONITOR LrzARDS 80000
60000
50000 40000
o
1988
1989
19110
1991
11192
1993
(Sources: CITES trade statistics derived from the WCMC CITES trade database. WCMC, Cambridge. Luxmoore l'I at 19XX. Luxmoorc & Groombridge 1990. Jenkins & Broad IY<J4). NOI all monitor lizards are exploiled for their skins. in faci Ihe bruni of Ihe trade is borne by jusl five or six species. The waler monilor (V.SIItvawr) is Ihe mosl heavily collecled species. wilh Irade in almosl 2.5 million skins reporled in I<J90 al one. The major exporters of waler
51
Little Book of Monitor
Lizard~
lTlonitor skins are Indonesia, the Philippines and Thailand. Most skins are shipped through Singapore and find markets throughout the rest of eastern Asia, Europe and North America. In Africa the Nile monitor is the most heavily e)(ploited species with average trade in over 4()().O()() skins reported between 19RO and 19R5. Most slcins are e)(ported from Nigeria, Sudan, Mali and Cameroon and are sold in France, Italy and the U.S.A. Large scale trade in V('.wllfhemaricus (i .e. ValhiRuiari,~ and Vexanthemaficus) is also reported. with an average of xX,oon skins shipped each year between 19RO and 19R5. Most of these animals originated in Nigeria (VeX(lllfhemaficus) and, to a lesser e)(tent. Mali (V.exanthemaricus). Sudan (?) and South Africa (ValhiRuiaris). Most of the demand comes from France, other European nations and the USA .. Trade in the skins of desert monitors. Vgriseus, is often reported, but according to Auffenberg (19R2) its skin is too thin to make good leather and it is considered a very poor substitute for other monitor skins. Most animal skins traded as Vgriseus probably belong to the two completely protected species Vhengaiensis and V jlavescens. Commercial trade in these species has been outlawed since 1975, but several countries. notably Japan , ignored the ban and continued to import large quantities of their slcins until very recently. Between 19R3 and 1986 over one million Vhengaiensis skins were traded, mainly from India, Bangladesh and Thailand and almost all being exported to Japan. Trade in Vf/(/vescens skins amounted to an average of almost 120,000 skins per year between 1983 and 1911t). Almost all the skins originated in India and Bangladesh and again Japan was by far the largest consumer. It should be noted that all of the figures cited above refer to whole skins only, and do not include products made from monitor lizards or transactions reported by weight (often amounting to thousands of kilogrammes per year). Nor do they include over 1.5 million skins registered by Japanese customs between 1983 and 1987 but not declared to CITES. Furthermore Varanus skins are frequently misidentified in official declarations, with Asian species exported from African countries and vice versa. Exporters must find it very easy to deceive customs and CITES officials. During my investigations several Customs offices in several countries requested photographs depicting the various species, admitting they were unable to tell the difference between them. The most recent report of worldwide trade in reptile skins (Jenkins & Broad 1994) includes a single photograph of "Vsaivator", the most frequently encountered monitor in the skin trade, which is clearly misidentified and should have been labelled Vdumerilii, a species in which leather trade is unknown! The e)(ploitation of monitor lizards has largely been overlooked by Westerners. Most people do not consider monitor lizards to be cuddly animals and perhaps it is on account of their lack of fur that their slaughter does not incur the sympathy extended to other victims of the leather trade. As far as is known, not a single monitor lizard has been bred commercially and so the trade relies entirely on animals taken from the wild. Considering the vast numbers involved and the fact that only the skins of adults or subadults are suitable it can be presumed that the trade will eventually deplete numbers to the point that they become extinct in many areas. Recent large-scale extinctions have been suggested for several monitor lizards in Pakistan, India and Bangladesh but it is unclear whether their demise is attributable more to direct human predation than to habitat destruction. Studies of heavily exploited populations in Sumatra revealed some of the highest biomasses recorded for any lizard in the world (Erdelen 1911ll, 1991) and there are no clear cases of monitor populations being decimated in any part of South-East Asia or Africa because of the activities of the skin trade. Habitat destruction, on the other hand, can be held responsible for reduction in monitor lizard numbers in all countries in which they occur. It is difficult to think of the skin trade without revulsion, but the poverty in Africa and Southeast Asia is much more unpalatable. The potential of monitor lizards as a very profitable and sustainable resource must have occurred
52
Monitors & Mankind to many people, but no serious attempts at farming them on a conunercial scale appear to have been made. This may be due to the fact that they are still abundant in many areas , but if mankind is to continue to benefit from monitor lizards far into the future large scale captive breeding will be obligatory. Some well meaning but misinformed people condemn eating monitor lizards on the basis not of taste, but of morality. They consider that using them for food (or indeed for any purpose) contributes to their demise, but fail to appreciate that almost all of the countries where monitor lizards occur are unimaginably poorer than anywhere in North America or Europe. Because they have very little money they experience very high infant mortality and very low life expectancy. This forces them to adopt unsustainable economic practises that result in the destruction of local ecosystems, the extinction of many animals and plants and land fit for nothing but shanty-towns and refugee camps. Of all wild animals, monitor lizards are among the best suited to sustainable use. They breed and grow very quickly and many are equally happy living in pristine forest, a field of corn or a rubbish dump. They quickly establish large populations wherever adequate food is available and they are not fussy about their diets. Their flesh is extremely nutritious and most importantly, their skins are very valuable. The price of a pair of monitor lizard shoes in Italy or Japan would feed a family for a year in most parts of the world. Westerners who object to the use of any animal skins except those of cows and sheep often fail to appreciate that animals with no economic value are likely to find their right to existence questioned increasingly as the populations of poorer countries burgeon.
USES OF MAN BY MONITOR LIZARDS Humanity offers food and shelter to the monitor lizards. A few large monitors will eat people when given the opportunity, but most have to be content with buried corpses that they locate by smell and exhume. In many parts of the world graveyards have to be heavily protected against monitor lizards by packing the ground with clay or coral, or by enclosing the area within a strong fence (e.g. Taylor 1963). Only a few, very large, Komodo dragons are capable of catching and consuming an healthy adult, but smaJl children could potentially faU victim to a number of species. Monitors have an unfavourable reputation for stealing animals (usually young chickens) from man in most parts of the world and for this reason are often killed when encountered by fanners. In some cultures monitor lizards are tolerated rather than encouraged. Local customs often forbid the killing of monitor lizards for any reason, but their antisocial behaviour does not necessarily go unpunished. Cisse (1971) recalls that a Senegalese man who found a Nile monitor in his house helping itself to his breakfast eggs found himself unable to kill the intruder, but vented his anger by tying the animaJ up and giving it a sound thrashing with a belt before releasing it, bruised but otherwise unharmed . It remained in the vicinity, but never entered his house again. Monitor lizards love messy campers and tidy up a great deal of their mess, including scraps of food, faeces and, unfortunately, plastic bags and other inedible debris that smells of food. In many areas they seem aware of the habits of holiday makers, and consistently emerge just minutes after the last tourist bus has departed . Less shy individuals may actively solicit food from people and will even "beg" for food in a dog-like manner.
53
6
The Monitor Lizards of the World
VARANUS ACANTIIURUS Spin.v-Iailed goanna
Varanus acanthurus acanthurlls Roulenger IHHS Varanus aranthums brachyurlls Sternfeld 1919 Varanus aranr/lllntS ;nmfan;C/ls Mertens 19511
The spiny-tailed goanna is found throughout northern Australia (except the east of Queensland) and also inhabits many islands off the northern and western coasts. It may be ahsent from areas of the Northern Territory inhabited by Vharirji. Three subspecies have heen desuibed: V(/cQ"rhurus acanthurus from easterly parts of the range, Vaca"rhurus hmchYllnts from the west and V.acanrhurus insufanicus from Groote Eylandt and M;lrchinhar Island in the Gulf of Carpentaria. Storr (19110) did not consider Va.hrachyurus 10 he a valid suhspecies, but he remarked on peculiarities in specimens from some islands (Barrow and South Murion) off Western Australia. Case & Schwaner (1993) noted that animals from Barrow Island were significantly smaller than those on the mainland. Specimens frplll southern locations tend to be more brightly coloured and have shorter tails than those fmm the north . with populations in the north-west Kimberleys and on islands in the Gulf of Carpentaria being virtually black with only a few lighter markings (Storr 1980; King & Horner I<)X7). Colour and pattern do not differ significantly between juveniles and adults. They reach a maximum of about fiOcm TL (2Scm SVL). The spiny-tailed monitor lives in a variety of tropi cal and SUbtropical habitats and is rarticularly associated with rocky areas. However they will also live in trees (Stammer 1970) or in burrows (Swanson 1979) and have been collected from beneath spinifex grass (Smith I,}7(\). In stony areas they like to shelter in rock crevices (where they use their spiny tails to wedge themselves into inaccessible cracks) or in burrows under slabs of rock (where they use the tail base to block the burrow entrance). The spiny tail is wielded like a club with considerable force (Thompson & Hosmer 1963; Swanson 1979; Stanuner 1970; Auffenberg I<)X3a). The western "brachyurus" may be more arboreal in habit than "acanthurus". In areas without outlying rock they may spend the coolest parts of the year in tree hollows (Stammer I,}70). Stammer also records that the lizards take refuge in labyrinths of burrows covering about 0.Sm2 but only 20cm deep. Bustard's (1970) remarks that this species lives in colonies are thought actually to refer to V.storri (Greer 1989) but the lizards' dispositions in captivity suggest that they could live in close association with each other. Females are encountered as often as males. but may not grow to as large a size (King & Rhodes 1982; Fitch 1981). Mating occurs in the late dry season (August - November) and a single clutch of 2-11 eggs is laid which hatch during the wet season (December and January) (King & Rhodes 1982). A nest examined in the Northern Territory had been dug into a mound of bulldozed soil and consisted of an "s" shaped tunnel tenninating in an egg chamber 40cm below the surface. The tllnnel had been refilled with soil and the eight newly hatched youngsters were digging
54
~;I
e; ..,.,
~
c:] -
Little Book of Monitor Lizards themselves out (Husband 1979) . Wil son & Kn ow les (19g g) note that the severed tails of these animals are sometimes en<;ountered and suggest th at this armoured appendage is conside red inedible and discarded by predato rs. The spiny-tailed goanna feeds mainly on invertebrates (particularly orthopterans and beetles) and other lizards (geckoes, agamids and skinks). They are known to be cannibalistic in captivity and may eat smaller varanids in the wild. Most specimens examined contain less than three prey animal s in their stomac hs (Loso s & Greene 1988). The metabolic rate of this species is lower than that of similarly sized species, suggesting that they may catch a lot of food by ambushing it rather than actively seeking it out and chasing it down. Oxygen consumption has been measured at 0.057-0. 196 rnI of oxygen per kilo per hour (Dryden, Green elal I')gO ; Thomp so n & Withers 1994). Spiny-tailed goannas have been bred many times in <;aptivity and th ird and fourth generation ca ptive bred animals have been produced (e.g. Murphy 1972; Jauch 1984, Erdfelder I n4; Horn & Visser 19~9; Thissen 1991 , 1992; Vi sser 1993; Eidenmuller 1994). This monitor is easy to sex by lookillg for clusters of well developed spiny sca les on the tail base at either side of the vent in males. Unlike many monitors they seem to tolerate each other mos t of the time. Colonies of up to five animals can be housed in an enclosure with 1m2 of floor space but the animal s should be separated for a short period each year. Best results have been obtained by using ultra-violet light, a deep (20cm) sand substrate and simulating seasonal light and temperature changes. Winter temperatures as low as 14°C are safe. During the summer the animals (particularly the females) like to bask at high temperatures (up to 44°C). Mating behaviour usually coincides with the onset of spring. In captivity a second clutch of eggs may be laid shortly after the first. Eggs incubated in venniculite with high humidity (around 100%) at 26-32DC hali:h after 90-166 days. Spiny-tailed goannas thrive on a diet of large insects and sma ll rodents . Unequal sex ratios have been noticed in clutches incuba ted in captivity, prompting suggestions that the sex of hatchlings may be influenced by incubation temperature. Hatchlings weigh from 3.5-9g, probably depending large ly on the age and size of the female. They become sexually mature at around Ilcm SVL (King & Rhodes 1992) . Given good conditions they can attain this size in less than a year (Husband 1979). They can live for more than ten years in captivity (Snider & Bowler 1992).
VARANUS ALB/GULAR/S White-thruated munitur, Ruck leguaan, Tree leguaan.
VarallllS aibiglliaris aibiglliaris Daudin 1802 Schmidt 1933 Varanlls aibiglliaris angolensis VarallllS aibiglliaris microstictlls Boett ger 1893
The white-throated monitor is a big, sturcly lizard found in much of central and southelll Africa; Cenu'al African Republic, Sudan, Djibouti, Ethiopia, Somalia, Gabon, Congo Republic, Zaire, Uganda, Rwanda, Burundi, Kenya, Tanzania, Angola, Zambia, Malawi, Zimbabwe, Mozumbi4ue, Namibia, Botswana and South Africa. The species is apparently extinct in Lesotho (Luxmoore 1'1 al 1':iR~ and references therein). v.o('el/lIll1.1' (Heyden in Ruppell I X30) is recorded from sou thern Egypt and neighbouring countries and is probably closely related to V.exallCh1'mal;cu.\· (Anderson I X9~, Schmidt 1910. Hafez I ':in - see under
56
Monitors of the World
Vexanthematicus). TIlls monitor is found in a variety of dry habitats including steppes. prairies and savannahs but are absent from desert interiors, rainforests and thick scrub forests. Unlike Nile monitors, they appear to shun human settlements. These lizards were previously known as subspecies of Vexanthematicus, but have been separated on the basis of differences in hemipenal morphology (Bohme 1988, 1991). Three subspecies are currently recognised : Va.angolensis from Angola and the adjacent part of Zaire, Va.microstictus from eastern Africa (southern Sudan and Ethiopia south to Zimbabwe and Mozambique) and Va.albigularis from the remainder of the range. They can be distinguished by the number of scales around the body (75-95 in V.exanthematicus, 122-152 in Valbigularis microstictus, 137-167 in Va.albigularis and II 0-141 in Va.angolensis (Laurent 1964». V.exanthematicus ionodesi (Laurent 1964) from Tanzania is considered to be a description of juvenile V.alb;gularis (Strimple 1988/9). Valbigular;s is a very variable animal and whilst some people believe that it will eventually prove to be a complex of several species, others find variation between the subspecies to' be too continuous to warrant their recognition. Heck (1955) commented that two specimens caught in the same part of South Africa had very different colouration (slate-grey and red-brown) and Rese (l983b) reports that m;crost;ctus and albigularis will interbreed. In the literature Valb;gularis is often referred to as Vexanthematicus, creating considerable confusion. An excellent review of this fascinating group of monitor lizards can be found in Strimple (1988/l!9). Lengths of up to 213cm have been claimed for the white-throated monitor (Strimple 19811/9), but specimens of I90cm must be rare. The tail is only slightly longer than the head and body length in adults. In many areas they rarely exceed I OO-15Ocm (Stevenson-Hamilton 1947; De WaaI 1978; Auerbach 1985). Mean size of six examined by Bowker (1984) was 41 mm SVL and 2430g. Males may become longer and heavier than females. The largest male recorded in Orange Free State, South Africa was 126cm TL (6lcm SVL) and the largest female was 106cm TL (498cm SVL) (De WaaI 1978). In Etosha National Park, Namibia, largest male was 77cm SVL and 8kg, largest female 62cm SVL and 6.5kg (Alberts 1994). In captivity adults can become extremely obese and exceed 20kg in weight (Loveridge 1943; Branch 1(91). The largest specimens may come from Kenya and Uganda. In Namibia females become sexually mature at around 45cm SVL but in South Africa females of 35cm SVL can produl:e clutches of over ten eggs (Alberts 1994; Branch 1991). Hatchlings measure about 20cm TL and weigh 25- 30g. White-throated monitors seem equally at home on the ground or in trees. Their diets l:onsist largely of invertebrates (especially snails together with beetles, orthopterans, millipedes and scorpions) but they occasionally take larger prey such as other lizards, snakes (including puff adders and spitting cobra), frogs, toads, tortoise, birds, eggs, marrunaJs (including hedgehogs) and carrion (Hewitt 1937; Loveridge 1936, 1942; Fitzsimmons 1943; De Waal 1978; Root 1978; Losos & Greene 1987; Branch 1988, Branch 1991 ; Alberts 1994; Kaufman et al 1994; de Villiers, pers.comm.). It is considered by bird watchers to be more addicted to birds and their eggs than any other Asian or African varanid (Pitman 1962) and this has been substantiated by many direct observations (e.g. Stevenson-Hamilton 1947; Sweeny 1(52). Steyn (1992) suggests that goshawks follow monitor lizards in order to feed on animals disturbed by the lizards' foraging al:tivity. Its diet indicates that this is an active forager which eats any suitably-sized animal it encounters. Rose (1962) reports that the lizards will hide in a tree next to a mistletoe bush and ambush birds by slUnning them with a blow from the tail . He also reports thar a boy who mistook a rock leguaan's head for a stone
57
Little Book of Monitor Lizards and tried to throw it at an ox was knocked unconscious by a tail strike. Patterson (1987) suggest that males are territorial and records ritual combat involving opponents intertwining their nodies and attempting to bite each other. Bipedalism does not appear to have been ohserved in this species. although Horn c( al (1994) suggest that bipedal combat may occur. Mean active hody temperature of 32.3"C was recorded by Bowker (19R4). This bulky monitor shelters in burrows. rock crevices. abandoned tennite mounds or trees. They may be inactive throughout the winter months or during the driest parts of the year and thus build up large fat reserves over the spring and summer. Torpid white-throated monitors have been found sheltering in rock crevices and shallow burrows under rocks during the winter (Bates 1(90). Like other African varanids the clutch size is large. Branch (19R8) records a female whose 37 eggs accounted for almost half of her weight. In temperate areas eggs are usually laid in the spring and may overwinter and hatch the following spring (Branch 1(91). Eggs from female recent imported from Mozambique produced eggs in October (Shaw 1%3). Most eggs appear to be deposited in burrows (such as in abandoned nests of ground sljuirrels - Phillips and Packard 1994) but there are records of them ovipositing in ahandoned termite mounds (Gillet in Branch 1991) and suggestions that they nest in tree hollows (Cowles 1930). Up to 50 eggs may be laid per year (Branch 1991) but in the wild less than half of the eggs are likely to develop and hatch successfully (Phillips & Packard I'N4). A very detailed study of the white-throated monitor in South Africa was carried out by Alfred Brown in the late nineteenth century. but not published until a hundred years later (Branch 1(91). This monitor has often been attributed with a nomadic character. wandering over large areas in search of food (Hewitt 1939, Bowker 1984). In Namibia home range size has been estimated at 6.lkm 2 for females and 18.3km 2 for males (Alberts 1994). Here activity levels are highest during the wet season (January - April) and males are particularly active during the mating period (July-August) when they often walk more than 4km per day. During the dry season they typically move only about 50m per day. This study also demonstrated that males given supplemental food during the dry season are much more active than those who have to fend for themselves. In South Africa the white-throated monitor is most active between October and February (Branch 1991). Densities of white throated monitors have been estimated at 10-50 animals per km 2 in Kenya and a biomass of around 4S,OOOkg in 22,OOOkm 2 at Etosha National Park, Namibia (Western 1974, PhiUips 1<)91)*. The white-throated monitor has reproduced quite often in captivity and can be extremely prolific with up to 65 eggs laid by a single female in two clutches over six months (Anon 19R7; Bom & Bom 1987). At least 10m2 of floor space should be provided (Staedeli 1962; Visser 1981; Anon 1987; Van Duinen 1983; Rese 1983) and under these conditions animals of similar sizes can safely be housed together. They will accept a wide variety of foods including large insects, snails, eggs, small birds, freshwater fish and crustaceans and mammals. Ambient temperatures of 20-35OC are suitable, with hotter basking areas up to S()"C. Cooling the enclosure to 16-\8OC for a short period may trigger breeding behaviour when warmer conditions return. Courtship is not particularly violent and ' evidence from captives suggests that females may lay their eggs during the night (Van Duinen 1983; PhiUips
'See also Phillips (in press). SR
Monitors of the World & Packard 1(94). Eggs from healthy females will develop under a variety of incubation conditions (27-3 1°C) with humidities (measured as water potentials) of ISO - -I lOOK pa and hatch after 116-180 days. Damper conditions produce larger hatchlings whilst different temperatures produce hatchlings with different shaped heads. Data from 78 animals hatched at Iguana Zoo in Vlissingen, Netherlands suggested that warmer incubation temperatures produced females and cooler temperatures produced males (Anon 1987). This has not been substantiated and may be due to difficulties associated with accurately sexing the animals. Hatchlings grow rapidly and may reach sexual maturity within two years. Obviously females require enormous amounts of food if they are to produce their own body weight in eggs each year.
VARANVS BARITJ/ King & Horner 1987 White's dwarf goanna White's goanna (baritj is an aboriginal word for white and the lizard is named after its discoverer Dr Neville White) is a small spiny-tailed monitor known at present only from '0 the extreme north of the Northern Territory. It can be distinguished from V,acanthurus only on the basis of its pattern and colour. V.baritji lacks the light ocellated markings on the back associated with V.acanthurus and also lacks the light and dark dorsal neck stripes. V.baritji has a bright yellow underside, Like V.acanthurus it favours areas of rocky outcrops and has been collected under both limestone and granite. A specimen caught in early June laid three eggs in captivity. Maximum known length is 72cm TL (2Scm SVL) (King & Horner 1(87). According to Thissen (1992) Swanson's (1976) picture of V.acallthurus is actually V.baritji.
VARANVS BECCARI Doria 1874.
Black tree monitor, Beccari's monitor.
0",
Beccari's monitor is usually considered a subspecies of Varallus prasillUS. Sprackland (1990) considered it to be
a separate species on the basis of its entirely black colouration and more keeled neck scales. It may also reach a larger size than the emerald monitor with a maximum size of 34cm SVL, 94.Scm TL. Beccari's monitor is apparently found only on the Aru Islands and nothing is known of iL~ ecology. Like emerald monitors they are superbly adapted for an arboreal existence. They may inhabit mangroves swamps and crabs may form an important part of their diet (Pattullo, pers. comm.). In captivity they should be housed in the same manner as emerald monitors. Although the Aru Islands receive less rainfall than the rest of New Guinea the animals appreciate water as much as their green relatives. Like other members of the prasinus group, Beccari's monitors are sociable animals and can usually be housed in groups without incident. The presence of more than one male may increase the chances of initiating courtship. Unusual apparent appeasing behaviour, in which the weaker animal rubs his chin on the dominant animal's pelvis and tail has been observed in these animals (Branham & Wheeler, pers. comm.). Breeding has been reported on a few occasions (Branham, pers, comm., Wanner 1991, Eiderunuller & Wicker 1992; Biebl I994b). Clutches of up to six eggs measuring 4.S X I.Scm are laid, which hatch after about 240 days at 27.7()C and 172-203 days at 27 -3()°C. Hatchlings often possess a bright pattern consisting of rows of green or 59
Little Book of Monitor Lizarcis yellow spots which completely ciisappear within twelve weeks. Unfortunately most hatchlings prodllceci to ciate have ciieci after a short time. They may be unable to tolerate humidity that is too low or too high anci appear to be particularly susceptible to infections. Hatchlings should he hallcileci as little as possible anci houseci separately. These bonnie wee beasties will feed on a variety of insects anci occasional meals of small vertebrates. VARANUS BENGALENSIS
Varanlls bengalensis bengalensis Daudin 11102 Hengal monitur Varanlls bengalensis nebllloslls Grey III~I Chlllcied monitor The Ilame of this monitor lizarci is misleading, for it is one of the most wiciely distributeci of the living varanicis. The Bengal monitor inhabits river valleys in eastern Iran, Afghanistan and western Pakistan (Mertens 1942, 1959; Leviton & Ancierson 1':170; Luxmoore & Groombridge 1990). Elsewhere in Pakistan it is widespread in many ciifferent habitats, but reaches greatest abundance in agricultural areas (Auffenberg et (/1 I'J'J I ). It is similarly ubiquitous in India, Nepal, Sri Lanka, Bangladesh and Burma, found from ciesert fringes to rainforests, but is most common in farmlands anci dry, open forests (Smith II}JO; Deraniyagala 11}31; Khan 1989). A ciifferent form of the Bengal monitor is found from southern parts of Burma and Vietnam, throughout Kampuchea anci Peninsular Malaysia. Sumatra. Java and the Suncia Islands. Clouded monitors are not found in Singapore ;lnci although they are present on some islands in the South China Sea they are absent from Borneo. They are founci in a similar variety of habitats as the nominate race, including pristine rainforest, but in the extreme south-east of their range they are absent from wetter areas (Mertens 11}42, I1}59; Lekagul 1969; Brygoo 1987, 1990; Auffenberg 1988; Jasmi I'JXX). The Bengal monitor is distinguished from the clouded monitor by having larger scales above the eyes and fewer scales around the body (Mertens 1942). The skull of V.n .hI'IIK(liellsis is described in detail by Bhal (1937). In pattern these lizards show enonnous variation. Adult Bengal monitors are black, dark grey or brown, with varying amounts of lighter pattern over the back. Hatchlings are said to be dull orange or light brown and boldly banded with black and yellow over the body and tail (Minton 1966; Khan 1988). Adult cloucied monitors are much lighter in colour, ranging from light grey to dirty-yellow, with varying amounts of speckled pattern. Juveniles are sometimes darker than olcier specimens (Smith 1930; Nutphand). As in other monitors. the amount of pattern seems determined largely by the level of rainfall, with the plainest animals found in drier areas. These criteria alone (i.e. scalation and pattern) may be insufficient to assign many individuals to either nl'lIRalensis or nebuJosus, but it seems possible that the races are separate species (Auffenberg, pers. comm; Bohme 1988). However Gorman (1993) records captive breeding between the subspecies anci DeriniyagaJa (1957) notes that hatchlings show great variation in appearance. The Bengal monitor is often referred to incorrecdy as Varanus monitor (Sprackland 19R2). Yang & Simin (1987) and Yang & Liu (1994) described Varanu.~ i,.,.iwndicu.~ from around the Irriwady river in southern China and Varanus vietnamensis from nonhern Vietnam on the basis of slight differences in scalation and pattern compared with V.mllllilor and V.nebulosu.~. Unfortunately no specimens are available for examination and the ciescriptions cio not make reference to Robert Mertens' comprehensive accounts of varanici taxonomy, relying mainly on much olcier works. These animals are certainly very closely related to V.b.bl'nRnlellsis anci V.b.nebulosu.~ and suggest that the range of this species extencis into China. 60
Monitors of the World
BengaVclouded monitors reach a maximum length of about IOOcm TL in Bangladesh (Khan 1988), 140cm in Sri Lanka (Deraniyagala 1931) and 160cm in Malaysia, where large specimens can weigh over IOkg (Jasmi 1988). Nutphand gives maximum size in Thailand as only 1000m TL and Smith (1930) suggested that specimens of over 2.4m occurred in the forests of northern Burma! Males of both varieties grow larger than females; Auffenberg (l979b) records average size of adult males as about 58cm SVL (150cm TL) and 2.7kg, females 46l:m SVL (l20cm TL) and 1.5kg. Average size of adults in southern Sri Lanka is 50cm SVL and 2.5kg, but specimens of almost Ilkg have been recorded (Wikramanayake & Green 1989; Deraniyagala 1931). A wild specimen in Malaysia caught by Harrison (1955) increased in size from 20l:m SVL, 109g, to 40.5cm SVL, 1850g after 22 months and contained 15 eggs. In captivity sexual maturity is attained within three or four years but the animals may not mature for five years or more in less favourable habitats (Auffenberg 1983c; 1986). A study in Sri Lanka showed that Bengal monitors spend the nights in burrows, where their body temperature drops below ambient The following morning they must raise their body temperatures by basking before commencing activity and for this reason they are rarely active early in the morning (although MWlsch (1987) found them feeding before 0600 hrs. elsewhere on the island) and most active in the afternoons when temperatures are highest Mean active body temPerature was 34.5OC. In contrast the water monitors that inhabit the same area spend the nights in thickets of vegetation or in the water, where they are able to maintain body temperatures higher than ambient Mean active body temperature of this species was only 30°C and so the lizards are able to begin activity without a long period of warming up. They are active mainly during the mornings, and as ambient temperatures increase towards midday they move to cooler areas (particularly in water or high on the branches of trees). When temperatures begin to fall in late afternoon the monitors may recommenre activity for a while, but as evening sets in they return to the water or to dense vegetation, which remain warm throughout the night. In this way the thermoregulatory preferences (and therefore the behavioural patterns) of the monitor lizards allow them to co exist in the same area without corning into direct competition (Wikramanayake & Green 19!!9). Dryden & Wikramanayake (1991) note that only younger Bengal monitors frequent the vicinity of rivers, and that adults are found in drier forest, scrublands and grasslands whilst water monitors do not usually venture far from the water. Both races of the Bengal monitor feed mainly on the ground, but clouded monitors in particular are excellent climbers (Taylor 1963). Even large adults can ascend vertical tree trunks with ease, and they are reported to be agile enough to stalk and capture roosting bat~ (Deraniyagala 1931; Smith 1935). However, despite their large size, these lizards get most of their nutrition from tiny prey and feed mainly on beetles, grubs, orthopterans, sco'l'ions, snails, ants and other small invertebrates, which are consumed in enormous numbers. The lizards collect ants and similar sized prey by licking them up with the tongue. Vertebrate prey are comparatively rare, but include frogs, molluscs, fish, lizards, snakes (including cobras) and small mammals. The monitors often use their tongues to collect small insel:ts and fUld much of their food by rooting the ground, especially under cow pats and in leaf litter. They often forage in human rubbish dumps and occasionally take carrion (Henry 1912; Williams 1935; Brongersoma 1947; Deraniyagala 1953; Harrison 1955; Bharatan 1971; Sharma & Vazirani 1977; Sharma 1982; Losos & Greene 1988; Auffenberg & Ipe 1983; Auffenberg el al 19<}1). Feeding behaviour in captivity is discussed in Auffenberg (1983c). Around Lake
61
Little Dook of Monitor Lizards H:liiji in Pakistan . Bengal monitors often rest on floating vegetation and spend most of their lime close to the water. although they take almost all of their food from dry land (Auffenberg (.( (/1 1991). In temperate region s activity is halted or reduced during the cooler months whilst the tropical 1/l'IJUloslis may be active throughout the year. Bengal monitors shelter in hurrows or crevices in rocks and buildings, whilst clouded monitors prefer tree hollows. Both races are known to take refuge in abandoned tennite mounds and both will frequent human hahitations (Annandale 1921: Mahendra 1l)31 : D'Abreu 1933: Auffenberg 19R3a; Dryden & Wikr:lIl1anayake I'N In. Ohser vations in captivity show that males are more active than females, spending an average or 4.5 hours a day moving about, compared to 2.85 hours for females (Auffenberg 197%). Males also consume more food (up to I R% of their own body weight) and therefore grow fa ster than females. but a consequence of their high activity levels may be that they suffer higher rat es of predation. Around Lake Haliji home ranges are around 53,OOOm 2 for males and 44'(X)(hn 2 for females. In less productive areas home ranges can exceed 300,OOOm2 (Auffenherg l'f ((I Il)l) I).
-.
~I
"I '1
Ritual combat is described by Ali (1944) and R.Y. Deraniyagala (1953) and takes place in tyrical hipedal fashion. Courtship and mating behaviour is described in Auffenberg (1983b). In ord er to male the male must completely immobilise the female, who may struggle vigourous to escape, and so only the strongest males are likely to succeed. According to Auffenberg ef 01 (Il)l) I) pair bonding occurs in this species and fecal signals play an important role in social behaviour. Annandale (1922) reports that pairs of monitors are often found together. In northern parts of their range Bengal monitors reproduce during the wet season (Minton 19fifi). In Sri Lanka most eggs are laid between January and April, but some may be produced at other times of the year (Deraniyagala 1953). In Thailand eggs are laid through the year and Nutpand suggests that three clutches may be produced by a female over this period. In the northern parts of the range eggs may be laid in burrows, teonitaria or rotten logs (Deraniyagala 1l)5R, Auffenberg 1983a) but in Thailand an active teonite mound is the usual choice of nest site (Nabhitabhata, pers.comm.). Auffenberg (l983a) suggests that females may return to the same places each year to lay eggs. Maximum clutch size is usually co nsidered to be 30 (e.g. Smith 1930, 1935, Deraniyagala 1953). Incubation times in the wild are not well documented; Deraniyagala (1958) reports that eggs laid in December had developed after five months. Vijaya (1985) found eggs in September that hatched in July. Young Bengal monitors are very secretive. According to Auffenberg (1983a) the hatchlings remain in a group with their brothers and sisters for at least several months after hatching. They spend almost all of their time in trees and are entirely insectivorous. For many years Bengal and clouded monitors have been collected on a large scale for their meat and skins. The meat of this species is reputed to be particularly sweet and easy to digest and for this reason it is often given to invalids (Deraniyagala 1953). They are not ea~ily attrac ted to carrion . as is the water monitor, and are usually collected from their burrows (D'Abreu 1l)32) In India and Sri Lanka, where water monitors are considered inedible, the Bengal monitor is consumed with delight Around Kerala in southern India it foons a major part of many peoples diet (Luxmoore & Groombridge 1990) and in Thailand and Vietnam the flesh is often considered superior to th at of the water monitor (Deraniyagala 1931, Darevsky pers.comm.). Their skins are also highly prized, particularly the dark skins of sre<; imens from Bengal. The adverse effect of this heavy exploitation on populations was fITst documented more than 50 years ago (Deraniyagala 1931; Champion 1935) and the animals fi2
'I
~
= ~
MOnitors <)f the World have now been exterminated in parts of Sri Lanka , India and Bangladesh. (Auffenberg 1986: Sarker 1%7). Saxena (1993) noted that the number of road-killed monitor lizards decreased s harply during the 19);0's. However they are still common in many areas: Khan (1988) estimated densities of Bengal monitors in suitable habitats within Bangladesh as being around 13 per km 2, Das (1988) saw up to 20 specimens in an hour in parts of Bengal and in Thailand and Malay sia the s pecies is still very widespread (Nabhitabhata, pers.comm; pers. obs.). Whe n commercial trade in the spec ies was outlawed by CITES in 1975 many counrries ignored the ban. Ten years la ter Japan was still importing hundreds of thousands of s kins from Bang ladesh, Pakistan Thailand and Malaysia (Luxmoore & Groombridge 1990). In Indonesian they are known as biawak nyambak (wandering monitor) and in Malay as biawak puru (warty mo nitor). In Sri Lanka they are called talagoya or undumbu, in Burma kon-phut. These monitors are very hardy in captivity but reports of captive breeding are rare (McKeown, pers.co mm .. Klag & Kantz 1988: Koop in Horn & Visser 1989; Gorman 1993; Auffenberg. pers.co mm .). Mos t youngsters die before they hatch or shortly afterwards. a problem indicative of poorly nouri shed mothers. [n nature these animals are largely insectivorous but in captivity they often refuse to take smalJ prey items if they are also fed larger animals (Subba Rao & Kameswra Rao 1986). Therefore in captivity they should be fed on large numbers of different types of invertebrates. and this diet supplemented with less regular meals of birds. fish and mammals. All like to bask at high temperatures. but the clouded monitor can be expected to be less tolerant of cold nights than the Bengal monitor. Large amounts of space and furni shings that allow the lizards to search for food (particularly a soft subsrrate) are essential. Best res ults were obtained by Auffenberg. who maintained a group of monitors in greenhouses 18-150m2 Ma les were regularly moved from one group of females to another in order to stimulate courtship behaviour. Eggs were either left in piles of compost provided for nesting or inc ubated over water. and over 90% hatched successfully. At 29-30 oC tlley hatch after 235-254 days. at 30-34oC after 172-173 days. Clouded monitors have the potential to be ex rremely prolific in captivity, producing over 70 eggs in three clutches over a year (Bryson. pers. comm). According to Yadov & Rana (1988) females have shorter tails than males and can further be distinguished by looking for patches of scales arranged as pre-anal flaps in males that are absent in females (clearly i1lusrrated in Auffenberg el a/1991) . A recently published work on the Bengal monitor (Auffenberg 1994) represents one of the most detail studies of a lizard ever publi shed . Unfortunately it was not available at the time of going to press. Thi s book represents the third monograph on species of monitor lizard by Walter Auffenberg. whose conrribution to monitor lizard ecology is unsurpassed. Without doubt it will make fa sc inating reading.
63
Little Book of Monitor Lizards
VARANVS BOGERTI Hogert's monitor.
Mertens 1950
Bogert's monitor is usually considered a subspecies of \larallus prasillus but was raised to specific status by Spruckland (1991). It differs from V.prasinus in that it is entirely black and differs from V.beccari by 1\ having more ventral and midbody scale rows (87-90 and '1S-'19 vs. 70-79 and 81-86 in V.beccari). It has been recorded from Fergusson and Normanby Islands, south of Huon Gulf and St Aignan in the Louisade Archipelago. Live specimens are unknown and nothing its known of the lifestyle of this apparently highly arboreal monitor lizard.
...
VARANVS BREVICAVDA Short·tailed guanna.
'"
Boulenger 1898
The short-tailed goanna is the smallest living monitor lizard, and 4uite possibly the smallest species that has ever existed. They live in desert regions of Western Australia, Northern Territory and Queensland, most often in areas of spinifex. Maximum size is 23cm (12cm SVL) and gravid females may
weigh as much as 20g. A specimen 9.9cm SVL caught in January weighed 9.Sg. (Gow I Storr & Hanlon 1980; Storr & Hanlon 1985; Pianka 1972, pers.comm.).
n I;
Very little is known about this delightful little lizard. Although they are found over a wide area they do not seem to be common anywhere and comparatively few specimens are known. In the Great Victoria Desert they may be most active between November and January. Short t~iled goannas live in burrows or shelter under stones. In captivity they dig extensively. Like Dlher dwarf monitors they feed on lizards and invertebrates (orthopterans, beetles, caterpillars and termites) . However their diminutive size restricts them from feeding on many lizards and invertebrates form the bulk of their prey. They also feed on lizards' eggs, suggesting that they hunt for prey below ground. In captivity the short-tailed monitor is known to habitually grasp the tails of geckoes it is unable to overpower and swallow them when they are cast off. An active body temperature of 3S.4°C has been reported (Slater I'IM; Pianka 1970, 1'194; Schmida 1974). This specie s has been bred in captivity (Schl11ida 1'174, 1995). An enclosure of .7m 2 with a deep sand substrate is suitable. Light cycles and temperatures should fluctuate seasonally. Breeding coim;icles with the return of warm weather. Incredibly, females are capable of producing up to eight eggs (in three clutches) over six months. Eggs hatch after 42-RS days at temperatures of I ~-25"C. Hatchlings measure less than Scm TL and weight less than 3g. Sexually maturity is allained around X·'1cm SVL. In captivity they can grow to adult size within two years. Shon-tailed monitors are reported to be somewhat fussy in captivity; they will not take dead prey nor will they eat even the smallest manunals (Greer 1'189).
M
Monitors of the World
VARANVS CAVDOLINEATVS Boulenger 1885. Stripe-tailed goanna V.caudolineatus is a small monitor lizard that occurs only in Western Australia. It does not appear to live around the coast. nor on any offshore islands (Storr 1980). Favoured habitats are grasslands. shrublands and woodlands and it appears to inhabit a wide range of Acacia and spinifex dominated habitats (Storr & Harold 1978; Storr & Hanlon 1980; Pianka 1969; Schmid a 1975). They are usually found beneath bark or in tree hollows and in areas with rock outcrops they take shelter in vertical and. to a lesser extent, horizontal crevices. In the Pilbara they are said to inhabit river banks (Bush 1987 & pers.comm.. ) but they are also found in very dry areas. For shelter they prefer very small spaces which they can wedge themselves into (Bennett 1991; Thompson 1993). The stripe-tailed goanna reaches a maximum size of about 32cm TL. A specimen I examined at Wanjarri in March measured II.2cm SVL (tail 13.5cm) and weighed 4.5g. Smith (1988) records the weight of a heavily gravid female as 37g. The tail of V.caudolineatus does not possess spines. but the scales are often strongly keeled. Storr (1980) noted that specimens from more northerly locations grow larger and more closely resemble V.gilleni. The stripe-tailed goanna is usually encountered in trees but may find most of its food on the ground. Its diet consists entirely of invertebrates (roaches. orthopterans. spiders. scorpions. centipedes and lepidopterans) and other lizards (geckoes and skinks) (Pianka 1969. 1994; Losos & Greene 1988; Thompson 1993). They commonly eat the tails of geckoes that are otherwise too big to swallow. Pianka (1969) found that they were active only during the hottest months of the year and suggested that the clutch of 4-5 eggs was laid in December. Smith (1988) collected a gravid female in late October that laid four eggs a month later weighing 12.4g in total (over a third of the body weight). In the desert their major enemies are probably larger goannas (Pianka 1994). A study by Thompson (1993) found that stripe-tailed goannas may live in close association with each other (he found four specimens in 0.OO5krn2 ). Because of their love of tight spa(;Cs the use of radiotransmitters to track their movements is impracti~al. Thompson got round this problem by marking the animals with small amounts of labelled sodium and tracking them with a Geiger counter. He found that the lizards were only active during the wannest part of the day (Le. at temperatures of 3O-45.5°C) and moved only short distances compared with other species of a similar size (average of 34m from one tree shelter to another) and would remain in the same tree for as long as 15 days (average of 3 days). Mean active body temperature of /0 specimens was 37 .8OC (Pianka 1982). Ritual combat is described by Thompson et al 1992. Other than the account given by Smith (198M) whose eggs failed to hall:h there is very little in the literature con(;Cming the care of this species in captivity (Minke 1914; Schmida 1975). Males and females look identical and may be very tolerant of each other. A diet of insects and tiny mammals should be suitable. Because of the small size and relatively sedentary behaviour of this species they can be kept in srnaffer enclosures (0.5- I m 2) providing they have the opportunity to climb and hide above the ground.
65
Little Book of Monitor Lizards
VARANUS DOREANUS IIlue-tailed monitor
Varanus doreanus doreanus Meyer 11174
Varanus doreanus jinschi flohme, Horn &
Zei~ler 1994.
.....
The rediscovery of the blue-tailed monitor is the latest in an exciting series of discoveries by Wolfgang Bohme and Georg Horn. Described and forgotten. the holotype had been destroyed by a wartime bomb, but the precise description given by Meyer allowed the recent workers to identify it as identilAll to their new-found species (Bohme et at 1994). The blue tailed monitor appears to be closely related to the mangrove monitor, V.indicus. and can be distinguished from this and other, similar, species by the smaller. more numerous, scales over the back , a brightly marbled underside, white tongue and a striped tail. Specimens are known from all over New Guinea and the islands of New Britain and Biak. The blue-tailed monitor appears to be restricted to intact forests and has been seen foraging on the ground. When threatened they do not take to water, as is almost invariably the case with the mangrove monitor. They can be tempted out of hiding with carrion or turtle eggs. V.doreanus finschi from the island of New Britain has a marked, rather than white, throat. Blue-tailed monitors are exported to Europe and North America, usually under the name Kalabeck's monitor. In captivity they require a spacious enclosure that allows them to climb and a warm, humid climate.
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VARANUS DUMERILII Schlegel 11139 Humeril's monitor
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Oumeril's monitor is a very mysterious animal. It is found ~-~p in southern parts of Burma, Thailand, Malaysia, Borneo, Sumatra and many smaller neighbouring islands including Natu, Bangka and BeJlitung. Locality data can be found in Mertens 1942, Brandenberg (I<)K). Sprackland (19'}3), Bennett (I 995a) and Bennett & Lim (in press). Smith (1930) said that they were particularly abundant on Kau- Ye-Kyun Island in the Mergui Archipelago. It is hoped that the Myanmar authorities will eventually give their pennission to allow a study of this beautiful creature to be conducted in the Mergui Islands. This monitor appears to be the rarest, or at least the most inconspicuous, varanid in all the countries it inhabits. They may be most common in mangrove swamps, but are also found in f-orests far from the coast. Maximum size is about 135cm TL. A breeding pair maintained in captivity measured 130em TL, 2'}50g (male) and I()(km, 2300g (female) (Radford & Paine 1989). Wild animals of JOcm SVL weigh about Ikg (Lim, pers comm.). Very little is known about the natural history of this intriguing monitor lizard (although a detailed account of its pelvic muscles can be found in Akita (1992». Smith (1930) records that they will take refuge in the sea to escape from dogs and Nutphand notes that they will climb trees when disturbed. Stomach contents of animals collected in mangroves are composed largely of crabs (Brandenberg 1983, Losos & Greene 1988) and Krebs (1979) considered them to be specialised crab eaters, noting that the nostrils can be sealed when the fi6
Monitors of the World animals are underwater and that the teeth are adept at piercing tough shells. According to Auffenberg (1981) they feed large] y on insects collected on the ground in inland forests. Ants and birds have also been suggested as prey (Barbour 1921, Pitman 1962). Raven's (1946) record of monitors feeding on turtle eggs on an island off Borneo was interpreted as V.dumeriJii by Neill (1962). Typical, bipedal combat has been recorded between males (Davis & Darling 1986). In captivity youngsters may bury themselves when given the opportunity (Horn & Schulz 1977). Nutphand claimed that this lizard was the least active of the monitors found in lbailand, spending most of its time in rock crevices and tree hollows and using the same retreats consistently. Both he and Lekagul (1969) considered it to be more common than the rough-necked monitor. It is quite possible that populations of both species have been seriously depleted by the destruction of forests, but Dumeril's monitor, at least, is known to inhabit areas of human habitation and so they appear to be able to swvive away from pristine forest in some circumstances (Bennett & Lim in press). A study of these monitor lizards in their natural environment would be extremely rewarding. In Thailand they are known as Tut-too, or more properly, HalH:bang-kao (white jungle monitor). In Malaysia they are biawak kudong. The beautiful appearance of hatchling Dumeril's monitors is well known (ftrst described by Horn & Schulz 1977) but no satisfactory explanation for the purpose of this bright colouring is available (see Chapter 4). In some areas youngsters have yellow, rather than orange heads (Auffenberg, pers. comm.). Dumeril's monitors make hardy captives, known to swvive for over 20 years (Grossman, pers. comm.), but reported breeding success with this species is rare (Zinunennann 1986; Radford & Paine 1989; Frost 1995; Connors, pers. comm.). They are not particularly aggressive but in cramped confmes the weaker animals are likely to suffer. Groups of three or four specimens can be housed in an enclosure of 8m2, but breeding has occurred in enclosures as small as 2.4m2 . Dumeril's monitor is an excellent climber and also shows great fondness for water. They may prefer basking spots in the mid to high 30s rather than 400C or above, but should be allowed to bask at the highest temperature they find a<:<:eptable. An ambient temperature of 25-32°C is suitable. Their diet should consist of insects, earthworms, crabs, fish, small manunals, birds and eggs together with a good vitamin and mineral supplement. In North America breeding usually occurs in October even when artificial lights cycles are in use. Clutches can contain as many as 23 eggs and may be laid over several days or weeks. More than one clutch can be produced in a year. Eggs incubated at 28°C hatch after 203-215 days, at 26.7-30OC after 215-222 days and at 25-30 oC after 234 days. In light of these figures Wong's (in Bennett 1995a) incubation period of 105-115 days seems impossibly short. Egg development does not always proceed smoothly, but the problem <:an probably be minimised by feeding the female on a rich and varied diet and ensuring that the incubation medium never becomes dry. Good results have been obtained using a vermiculite to water ratio of 5:6 or 5:8. Hatchlings measure about 18cm TL (8<:m SVL) and weigh 10-20g, presumably depending on hwnidity during in<:ubation. The youngsters <:an loose their bright colours after as little as six weeks and 'after five months <:an attain 13cm SVL. Youngsters should be provided with just enough water to immerse themselves and given damp substrate to hide in. Biebl (1995) suggests that Dumeril's monitors mark their territory in captivity. The subspecies V.dumeriJii heterophoJis was described by Boulenger in 11192 from animals <:ollected in northern Borneo. ,It is said to differ from the nominate ra<:e by having s<:ales of many different sizes over the back. Both Brandenberg (ln3) and Sprackland (1993) suggest that the differences are too slight to warrant use of the name heterophoJis. 67
Lillie Book of Monitor Lizards
VARANUS EREMIUS Pygmy desert guanna
Lucas & Frust 11195.
This husy little monitor is one of the most widespread of the pygmy goannas. It lives in desert and semi-desert areas of Western Australia. Northern Territory and South Australia but its uccurrem:e in Queensland is uncertain (Pianka 1%8; Houston 1l)7X: Storr 19XO: Storr & Harold 19RO). This is a ground-loving goanna that is often ..:ommon in areas of spinifex, and rarer in mulga-dominated habitats. They reach a maximum size of 4ticln (17..:m SVL). A specimen caught in January (9.6cm SVL) weighed II .Xg. A gravid female caught in February (14.4cm SVL) weighed 3R.3g (Pianka pers .colmn. ). The only populations to have been studied are those in the deserts of Western Australia. Here the pygmy desert goanna is active throughout the year, unlike most of its counterparts. They reach the peak of their activity during the late winter and early spring. During the summer they remain below ground during the warmest part of the day and are most active early in the morning. Mean body temperature of 53 active animals was 37.5 0 C. This guanna spend its life on the ground and rarely climbs trees. They prey largely on other li zards (espedally skinks) but they also eat orthopterans and small numbers of scorpions, centipedes, roa..: hes and caterpillars. They can cover large distances (almost I km per day) exploring burrows in search of prey. They may also hide in spinifex and ambush other lizards as they pass. In the Great Victoria desert they are often found in the labyrinth-like burrows of EgI'I'lIill skinks. Mating oc..:urs in the spring and 3-4 eggs (possibly as many as 6) are laid afOund January and February. Preferred nest sites are unknown. The eggs probably hatch after .3-4 months . Hatl:hlings measure about 6.5cm SVL and sexual maturity is reached at 11 12un SVL (Pianka 19tiX, 1971, 19R2, 1994; Losos & Greene 1988; Thompson & Hosmer I%~).
Nothing has been published about the care of this lively little goanna in captivity. A spacious t:ndosure (at least 1m2) with a deep sand substrate should be provided. Males might grow slightly larger than females but there are no obvious differences between the sexes. Care should be taken when housing these lizards together because they are undoubtedly ..:annibalisti..: when given the opportunity. They feed on comparatively large prey in the wild and should he fed on a diet of big insects and vertebrates.
oX
Monitors of the World
VARANUS EXANTHEMATICUS Bose 1792
Buses monitor lizard Bose's monitor lizard is the smallest and most poorly known African varanid. Although it is regularly available in the wildlife trade, details of its natural history are searce. Virtually all that is written about V.exanlhematieus in the literature actually refers to the larger white-throated monitor, V.a/bigularis. They can be distinguished by the nlllllbu of scales around the body (see under V.a/biguJaris) and by the enlarged, flattened neck scales often present in specimens of Bose's monitor. Mertens (1942) and other authors thereafter have given the range of Bose's monitor as extending from Senegal as far as Eritrea and northern Zaire. The species is well known throughout the grasslands of West Africa, but its distribution in central and eastern parts of the continent is less certain. Bose's monitor does not occur in rainforests nor in desens, and thus the northern and southern limits of its distribution are restricted by the Sahara and the belt of rainforest that covers much of central Africa. Most of the live specimens come from the isolated belt of savannah along the southern coast of West Africa, particularly from Ghana and Togo. Sclunidt (1919) recognised the species V.oeellatus Heyden 1830 for the "exanthematieus" type animals from eastern parts of the range (Sudan and possibly southern Egypt), but Mertens, who cites many locations in Sudan, considered these animals to be typical V.exanthematieus. However animals from this region are recorded as eating birds (Piunan 1962), a habit associated with the larger white-throated monitor rather than its smaller cousin. Anderson (1898) and Muller (1905) also expressed the opinion that V.oeellatus was more similar to V.a/biguJaris or "V.mierostietus" than to V.exanthematieus. Schmidt (1919) recorded Bose's monitors from near Garamba in Zaire and included a picture of a specimen which clearly fits this deseription. There is no evidence that Bose's monitor and the white-throated monitor occur anywhere together, but the exact limits of their distribution and the true identity of V.ocellatus have not been detennined. Bosc's monitor can reach a total length of over 1000m, but such specimens must be rare in the wild. However Yeboah (1993) records average length of 16 adults in Ghana to be 130cm TL and there is an enonnous specimen from Togo in the collection of the Koenig Museum in Bonn. A rather thin specimen we found in Ghana measured 41cm SVL and weighed only 975g. In good condition this animal may have weighed twice as much. Bose's monitors can accumulate massive fat reserves and obese specimens are common in captivity, often weighing in excess of 6kg. Females tend to be smaller, but more heavily bodied, than males and may have slightly shorter tails. Cisse (1976) found females as small as 500g in Senegal that contained eggs. Bose's monitor is a shy animal. Its small size, highly seasonal patterns of activity, undistinguished colouration and secretive habits mean that they are easily overlooked and often considered rare in areas where they are actually very abundant. Unlike Nile monitors. they avoid human habitations and it is very rare to encounter one above ground. other than to see them dashing across roads. The most complete study of this species was conducted in Senegal by Cisse (1971, 1972, 1976). Here the animals have a strongly seasonal activity pattern, fasting and remaining in shelters for six months of the year. from December until late Mayor early June, when the weather gets cooler and then becomes very hot. Where uees 69
Little Book of Monitor Lizards areavailahle they are used for shelter, elsewhere they take refuge in burrows (especially those dug by ground squirrels) or abandoned tennite mounds. Activity commences with the beginning of the rains and reaches its peak from july to October, when most food is consumed and mating occurs. Females can produce up to 41 eggs in a single clutch, which are laid in October and November and probably hatch in June or July the following year. Beetle larvae, millipedes and centipedes are the most common food early in the wet season and are replaced by increasing numbers of orthopterans later in the year. they are also rel:orded as eating mantids, hymenopterans, lepidopterans, scorpions, snails and the eggs of hoth agamids and their own kind. Most prey are found on tree branches, in soft earth or under ruminant dung. During the height of feeding activity ingested prey can account for over 10% of the body weight. A similar diet is reported in Ghana by Yeboah (l993) who also found that crabs were included in the diet There are no published records of egglaying sites in this species, but according to trappers in Ghana, who collect the eggs for artificial incubation, most nests are located under the ground in elevated areas (especially on hillsides). Eggs are also found in tennite mounds, but it is unclear whether these mounds are active or abandoned. In the coastal grasslands of Ghana young Bose's monitors reach their greatest abundance in farmlands with sandy soils, where up to 55 specimens can be found in less than ISO,OOOm2 durin£ August and September. equivalent to a biomass of 36kg of baby monitor lizards per km ! The animals shelter in shallow burrows, particularly those of large mole crickets, and often take to trees, especially in wet weather. Where food is abundant most individuals remain in areas of less than 500m 2 for periods of at least five weeks. Their diets consist largely of orthopterans but they also eat frogs, snai Is and scorpions, together with lesser quantities of beetles and wasps. The youngsters grow very quicldy'and within four months some are large enough to swallow their smaller siblings. Between 0900 and 1630 hrs. body temperatures range from 26.5-38°C. According to Cisse (1971) the animals may emerge from their retreats and conunence activity without basking, but in undisturbed grasslands in Ghana we found what appeared to be cleared basking sites located very close to monitor burrows. Yeboah (l993) found that Bose's monitors commenced activity about an hour before Nile monitors where the animals were sympatril:. In August and September, when Bosc's monitors in Senegal are said to be most al:tive. adult lizards in Ghana appear be largely immobile and do very little feeding (Bennett & Akonnor 1995 & ms). Schmidt (1919) stated that in Zaire Bosc's monitors may be inactive during the dry season. He also provided a picture of a specimen feigning death with one of its hind feet in its mouth. Of 250 specimens caught by us, none attempted to play dead, but one that was presumed to have been injured during capture assumed an identical posture to that in Schmidt's photograph, from which it had failed to recover after 4 days. In l:aptivity Bose's monitor has a reputation for being a lethargic, if not boring, animal which can be attributed to their need for a reduction in activity during part of the year. The easy availability, small size and comparatively docile disposition of this species makes it the most suitable monitor lizard for keeping at home. The animals are generally very tolerant of each other and colonies can be maintained providing none are so small that they may be regarded as food by others. Many of the animals exported from West Africa are described as captive hred, but the usual way of collecting them is to excavate fertile eggs from the wild and hatch them artificially before shipping them to Europe and the USA. Captive breeding or successful incubation of eggs laid by wild-caught females has been described by several authors (Linley 70
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Lillie Book of Monitor Lizards in BenneiL 1'ilJ2d . Bayless & Huffaker 1\1\12, Rowell 1\1\14, Roder & Horn 1\1\14, Bayless 1')<)4). An enclosure as small as 1m2 is sufficient to house a pair, providing that a suitable thermal gradient can be established (i.e. 17-40 oC during the day). Cisse (1\171) reported that even in captivity Bosc's monitors would refuse food and water throughout the dry season. Rowell (I \1\14) noted that hi s specimens went off food from November to February but many specimens will happily gorge themselves year-round and can become extremely obese. Eggs incubated at 32"C hatch after 127-132 days, at 29°C after 169-1 94 days. Hatchlings weigh about 109 and measure about 12cm in total. in captivity a varied diet should be provided, which reflects the animals' insectivorous diets. Although they do not appear to eat many vel!ebrates in the wild they will happily take small mammals in captivity. Juveniles should be fed as much food as they wiJ I eat, adults should be fed with care and intake reduced when th ey begin to look too fat.
VARANUS FLA VESCENS Hardwick & (irey 1827
Yelluw Munitor, Shurt-tued monitorThe ye llow monitor is a poorly known species and is considered to be one of the most endangered moni tor liz,u·ds. It is found only in Bangladesh, Nepal, india and Pakistan (Minton I\160; Smith I\132; Swan & Leviton 1%2; Auffenberg el til IlJ8lJ; Sarker 1987). Early reports of yellow moni tor lizards in Burma were never substantiated and they probably do not occur there now (Smith 1930). This species bears a very strong resembl ance to Bose's monitor, but its habitat and behaviour are very different. For a long time the yellow monitor was believed to be an inhabitant of dry areas (see Chapter 2) but it is now clear that they frequent areas of marshes and swamps, usually along the f100dpains or la rge rivers. These areas have been greatly modified by mankind for agric ultural purposes, especially in the last century, and thi s has lead to the disappearance of thi s species from Illany areas that it previously inhabited, including Agra in western Uttar Pradesh, India (S mith ILJ32; Auffenberg e/ a/ 198\1). Yellow monitors are sometimes found along streams in foothills but they appear to be unable to survive in mountainous areas. Although sand is the predolllinant substrate in most of the areas in which they occur, they appear to be intolerant of high sa lt concentrations and are therefore absent from coas ts. Khan (1988) estimated densities of yellow monitors in suitable habitats within Bangl adesh as being around 7. 5 per kn12
Yellow monitors reach a maximum length of about IOOcm. Th e longest reported by Auffenberg I'{ 01 (ILJXL)) was L)2cm (4lcm SVL), the heaviest I040g. Males do not grow appreciably larger than femal es. in Bangl adesh maximum len gth is usually 70-80cm TL (Sa rk er ILJX7). Hatchlings meu~ ure about 14.5cm (6.5cm SVL). Like Bosc's monitor the tail i\coJll purati ve ly sho rt (120-1 30% of SVL). Sexual maturity is reac hed at around 25cm SVL. Th e L'olour of thi s monit or lizard shows great variation, even among animals in the same area, with muny specimens showing red bands across the body. During the monsoon season the colours of both sexes become more intense. A description of the skull is given by Mertens ( 1')';<)) and descriptions of the hemipenal morph ology by Bohme (IlJ88) and Khan ( 19lJ3). tVlany of th e area s inhubiled by the yellow 1110nitor are ~u bject to extreme seasonal change. The animals appear to be 1110st active during the wetter purt of the year and least active in the 72
(SEa Il;)UEJpUIl EIPUJ ' J011UOW MOlldA
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Lillie Book of Monitor Lizards dry wimer (November - February). They shelter in burrows, crevices in river banks or termite mounds (Khan 1998. Auffenberg et al 1989). They may seal their burrow entrances with a plug of earth (Auffenberg. pers. comm.). They have very short toes and are not efficient climbers. During the wet season, when their habitats are flooded, yellow monitors spend much of their time in water, building up large fat reserves to sustain them through the winter. Their diet consists largely of frogs, toads, turtle eggs and lizard eggs. They also eat frogspawn . mammals, birds and their eggs and a range of invertebrates, especially beetles and earthworms (Sarker 1987; Losos & Greene 1988; Auffenberg et al 1989). According to Auffenberg et al they do not eat molluscs. although these are available in many areas. However Sarker (1987) records predation on crabs. Mating occurs in June and July and an average of 16 eggs (maximum of 30) are laid from August to October (Whitaker & Khan I':IX2; Auffenberg et al 1989). There is no evidence that they lay eggs in termite mounds. Theobald (1868 in Riley et al 1985) must be referring to the Bengal monitor when he claims that monitor lizards oviposit in termitaria in Burma. Eggs are probably deposited in burrows in elevated areas to avoid the possibility of nest flooding (Das, pers. comm.). In India hatchlings appear in March. Equal numbers of males and females have been reported, but males appear to be more active during the mating season. In captivity the yellow monitor is a relatively inactive species. The only published account of breeding is that of Visser (1985). A pair housed in a 15m2 enclosure were active only for half all hour in the mornings and half an hour in the afternoon . Eggs incubated at 30°C hatched after 14':1- 155 days. Unfortunately none of the youngsters survived. Like many monitor lizards. the yellow monitor likes to bask at very high temperatures (45°C). They should be provided with a soft substrate to dig in and enough water to submerge themselves for at least part of the year. In captivity in India three large frogs per week provide sufficient nutrition (Whitaker & Khan 1982), but vitamin and mineral supplements should be included in the di ets of animals kept indoors. A varied diet consisting of invertebrates, amphibians and small mammals is probably most suitable. In captivity they can live for over ten years. Despite the protected status of this lizard, trade in their sk.ins during the 1980s was reported at almost half a million per year. most of which were exported to Japan. The lizards' period of greatest activity coincides with a seasonal drop in employment in agricultural areas, and as a result many people collect their skins and sell them on to dealers (Chakraborty & Chakraborty 1987; Luxmoore & Groombridge 1990). The yellow monitor has probably disappeared from most of its previous range and. with the exception of the Komodo dragon. is considered the most endangered of the monitor lizards.
74
Monitors of the World VARANUS FLAV/RUFUS
Varanusflavirufus flavirufus Mertens 1958 Desert sand goanna Varanusflavirufus ssp. Sand goanna, goanna x Varanus gouldii was frr st described by Grey in 1838. Subsequently the animals from the extreme south of Australia were classified as a separate species (Y.rosenbergi) and a desert race was described (Y.gouldii flavirufus) . In 19RO Storr desaibed a new species Y.panopres, from animals previously assigned to Y.gouldii, based on differences in scalation, the presence of rows of dark spots over the back in the VpanopteJ rubidus and the presence of a banded tail tip in V.panopres panopres. Unfortunately the type specimen of V.gouldU is kept on the other side of the world (in London) and Storr did not see this animal before describing Vpanopres . In 1991 Bohme reported that the type specimen of Y.gouldii was identical to the animals described by Storr as a new species. As a result Vpanoples is considered a junior synonym of Y.gouldU and so the "new" species is entitled to the old name V.gouldU . Meanwhile the animals considered by Storr to belong to Y.gouldii have no valid scientific name. The next available name is V.j1avirufus, the name used by Mertens (1958) to describe the desert races of "V.gouldU". Thus the desert form becomes V .j1avirufus flavirufus, but the remaining races, which extend throughout Australia except for the extreme south, are currently nameless. This is highly unsatisfactory, because some people believe that the desert populations (V.j1avirufus) form a separate species from the animals in more mesic areas, and that the latter animals (which now have no valid scientific name) may be a complex of more than one species. This makes any description of the group ridiculously complicated. Biochemical comparisons of the group throughout Australia are needed to properly resolve these very serious taxonomic problems. When adequate material is available to allow comparison between races from allover Australia any revisions to the taxonomy will have to allocate new names to animals that have been written about for over ISO years. In summary; the animals referred to here as sand goannas or goanna x (V jlavirufus) are usually called Y.gouldii gouldii in the literature. The desert sand goanna V.j1avirulus flavirufus is usually called V.gouldU flavirufus. The animals known as V.panoples in the literature should be called V.gouldU, and the animals known as Y.gouldii in the literature actually belong to V jlavirufus. In older literature the name V.gouldU could describe the nameless actuality, V.gouldii gouldii, V.g.rubidus, V.g.horni, V jlavirufus or Y.rosenbergi. Often it is impossible to deduce the correct identity of the animals concerned . Here I have tried to omit such information.
V.j1avirufus is a very widespread species. They are found throughout Australia except for the extreme south (where they are replaced by Y.rosenbergi) the extreme south-east (where goannas appear to be entirely absent) and parts of central Western Au stralia and northern parts of Western Australia and Northern Territory (where they are replaced by Gould's goannas). The taxonomic status of the animals on the islands off the northern coast of Australia is not clear, but considering that Gould's goannas are common both on the northern coast and in southern New Guinea islands such as Groote Eylandt in the Gulf of Carpenteria are 4uile likely 10 belong to that spedes. Sand goannas are rarely sympatric with Gould's
75
Little Book of Monitor Lizards goannas. The two species appear to have different habitat requirements. The sand goanna is restricted to sandy soils whilst Gould's goanna prefers harder substrates. In general it can be said that they will inhabit any area with sandy ground, including forests, woodlands and scrublands. They are common in many areas (e.g. Onslow region (Storr & Hanlon 1985b), Bundaberg Region (Richardson 1976), Karrakatta Cemetery, Perth (Thompson 1992» but reported to be uncommon around Shark Bay (Storr & Harold 1978), on the Nullabor Plain, Western (Brooker & Wombey 197R) and in Merriwindi Forest (Bustard 196R). Additional location data can be found in Mertens 1958; Storr 19RO; Morris & Rice 1981; McUroy et al IlJX5: Grundke & Grundke I992b; Shea 1994). Pattern and colour vary throughout the range. Storr (19RO) suggested that specimens from the Kimberleys, which are darker and have less pattern than those found elsewhere, may constitute a separate race. The desert race V.f1avirufus flavirufus has a brighter pattern and more reddish colouration than the anonymous form. Intermediate specirnens are recorded from the Carnarvon Range and other desert fringes. Schmida (1985) notes that in the Sydney sandstone region Gould's goannas have a banded tail tip and are black with rows of prominent yellow spots. The banded tail tip is generally taken as being characteristic of Gould's goannas rather than sand goannas, which invariably has an unbanded tail tip. Around Jabiru in tropical Northern Territory the sand goanna reaches a length of at least 42.5cm (males) and 33cm (females) SVL and becomes sexually mature around 32cm (males) and 2Rcm (females) SVL (Shine 1986). In the same area Gould's goannas grow to at least 67cm SVL and matures at 39cm (males) and 3lcm (females) SVL. In the Barky Tablelands of Northern Territory sand goannas grow to at least 40cm SVL (Pengilly 1981). On Archer River in the Cape York Peninsula, Queensland they reach a total length of about 90cm (Glazebrook 1977). Three specimens collected in south-eastern Queensland weighed 1073 2562g (the largest had a total length of9lcm) (Johnson 1972, 1976) and specimens collected near Brisbane weighed between 89-1020g (Bartholomew & Tucker 1964). Largest found in a cemetery at Perth by Thompson (1992) was I 330g. Specimens of 30-35cm SVL weighed 300-750g (Thompson 1994). According to Storr (1980) the sand goanna reaches a total length of IOOcm in Western Australia. Thus there appears to be considerable variation in the max.imum size attained by these monitors in different areas. Although they will climb trees to escape from predators, this is primarily a ground dwelling lizard. In the labiru area the sand goanna is found only in sandy woodlands whereas Gould's goanna inhabits woodlands, grasslands and is most common around rivers and pools. The sand goanna feeds mainly on mammals (bandicoots, mice and rodent-like marsupials) and other reptiles (skinks, geckoes, agamids, frogs, monitor lizards, snakes and reptile eggs). They also feed on insects (particularly lepidopteran larvae, orthopterans and beetles), fish and I:rustaceans (Shine 1986). Around the McKinley River in Queensland sand goannas are important predators of freshwater crocodile eggs (Crocodylus Johnstoni) destroying up to 55% of their nests (Webb 1982). In Perth the diet of the sand goanna consists mainly of large orthopterans and spiders (Thompson in Pianka 1994). Elsewhere sand goannas are recorded to prey on birds and their eggs, tiger snakes. rabbits. frogs. scorpions, centipedes, wasps and ants, (Barrett 1928; FJeay 1950; White 1952; Berney 1936; Bustard 1970; Pengilley 1981; Losos & Green 19RR). Stammer (1981) records that specimen that mouthed a marine toad (RlIfo marin us) died shortly afterwards.
76
~
Monitors of the World The sand monitor is an exceUent digger. Its limbs are comparatively longer than those of other varanids and its feet are huge and equipped with powerful claws. Glazebrook (1977) records that a specimen excavated a hole 76cm deep in 20 minutes. [t probably retrieves much of its food from below the ground, suggesting that olfaction is at least as important as sight in prey detection. They have been seen striking at prey animals hiding under stones with the tail, in attempts to move them to more accessible spots (EidenmuUer, pers. comm.). Bustard (1970) found them particularly associated with rabbit warrens. He uses the name racehorse goanna (by which V.tristis is also sometimes known) in reference to the speed at which they move over flat ground, and describes their ability to run bipedaUy for short periods. Pianka (1970) notes that when walking nonnaUy desert specimens they do not drag their tails. However bulkier animals from wetter habitats appear to leave a clear tail trail (SprackJand 1992). Ritual combat is described by Thompson et al (1992). Ln tropical areas eggs are laid in the wet season (January and February), in temperate areas during the spring and early summer (Shine 1986; Thompson 1994). Clutches comprise of between 3-11 eggs, measuring an average of about 6X3cm (Shine 1986). Berney (1936) records a specimen that laid five eggs in October (preswnably in southern Queensland). He believed that the lizard might have picked up three eggs in its mouth and carried them to another hole when it was disturbed. A 60cm TL female laid eight eggs in captivity (Barnett 1979), another laid seven eggs (Irwin 1986). The sand monitor may oviposit in active or abandoned tennite mounds when these are available (Cogger 1967; Bustard 1970; Green & King 1993). In temperate areas the Lizards' activity is greatly reduced during the coldest months and even during the warmer months activity may be restricted to early morning and late afternoon (Green & King 1978). In tropical northern Australia sand goannas may have a similarly restricted activity pattern, with most movement during the mornings (Shine 1986). Ln South Australia sand goannas are most active during the swnrner. Daily activity ranges vary between 6,100 and 32,Soom2 depending on season (Green & King 1978). At a cemetery in Perth Thompson (1992) estimated foraging areas over 4- 18 days to be between 841 and 13,100.-n2. In this habitat they moved to new areas every few days. Where leaf litter (which contained most of their prey) was abundant the Lizards tended to forage in smaller areas. During the breeding season activity area averaged 9O,OOOm2 with the larger animals covering greater areas (Thompson 1994). In the Northern Territory Pengilley (1981) coUected road killed specimens and found a bias of 4: I in favour of males. Active body temperatures of sand goannas measured in the wild average 37.7°C in the Great Victoria Desert, with body temperatures as high as 44.7OC recorded (Pianka 1994). Mean body temperatures of 34.4-36.2OC are recorded by Light et al (1966). Telemetric studies have shown a range of 27.2-38.IOC (King 1980). In laboratory studies Johnson (1972) found that animals from central 'Queensland tolerated body temperatures of up to 40°C (head temperatures of 37.6OC) without signs of distress. The desert sand goanna (V j/avirufus flavirufus) is found in desert regions of Western Australia, Northern Territory and South Australia. Storr (1980) considered the variation between this race and the nameless variety to be too gradual to warrant different names. However the limited infonnation available suggests that the desert form leads a very different life to its counterpart in wetter areas. Desert sand goannas rarely exceed loocm in total length. None of the specimens I have seen possess the bulk of adult V.rosellbergi or the nameless race. The largest specimen found by
77
Little Book of Monitor Lizards Thompson & Hosmer ( I Yfi3) in the Great Sandy Desert measured 76.4cm TL. Those found ill the Great Victoria desert have an average SVL of 32cm. with sexual maturity attained at around 25cm SVL. Males have significantly larger heads than females and may reach slightly ~reater lengths, (Pianka IY94). A healthy specimen at Laverton. Western Australia, with a SVL of 31cm (75cm TL) weighed 3ROg during midsummer (pers. obs.). 111 the southern deserts at least. activity is restricted to the warmer months (September to February). The remainder of the year is spent underground. V.flavirUfus fTavirufus (and probably other closely related races) often shelter in shallow burrows that terminate just below the surface, allowing the animals to beak through the sand and escape if persued into the burrow (Bustard 1970; Greer 19R9). Breeding in the Great Victoria Desert occurs from September to November. Clutch size may be smaller than in the nominate race; Pianka (1<)')4) records a maximum of eight eggs in the Great Victoria Desert, Brooker & Wombey (I Y7X) record seven eggs from a female in the western Nullarbor Plain. Bred I (in Bustard InO) cites the case of a 107cm TL female from South Australia that laid II eggs in cnptivity. Hatchlings appear in January and February in many areas of Western Australia (Pianka 1970). Given the known incubation times in captivity it seems likely that the eggs take about a year to hatch in the wild. Sand goannas grow very quickly. Pianka (1994) suggests that they reach sexual maturity within a year. A specimen kept at the Dallas Zoo grew from 30cm to 75cm in 19 months (Murphy 1972). Irwin (1986) records that 27cm TL hatchlings grew to 33cm in three months. Eggs laid in captivity weigh 15-18g (Mitchell IYYO) and in the wild desert sand goannas weigh around 11-15g shortly after hatching (Pianka pers. comm.). Card (1994b) records that hatchling sand goannas can weigh as much as 3Xg. Mammals do not appear to be as important a food for the desert race as for those from wetter regions. In the desert lizards (agamids, sldnks, geckoes and varanids) and reptile eggs are their most important prey. Pianka (1994) list 27 species of lizards preyed upon in the Great Victoria Desert. They also eat large numbers of beetles, orthopterans, spiders and centipedes as well as other small invertebrates, mammals and nestling birds. They will feed on carrion when the opportunity arises and take poisoned bait intended for introduced pests. Juvenile are more insectivorous, feeding especially on roaches (Pianka 1970, 1994). Houston (I ':I7X) reports that the desert goanna will frequent temporary pools in the desert during the rains and are able to remain underwater for at least several minutes. The habit of standing bipedally is well documented for Gould's goanna, but my impression is that V.flavirufus .{1avirufus is less inclined to adopt a bipedal stance than Gould's goanna or goanna x. probably on account of its smaller body size. Sand goannas have been bred in captivity a number of times (Barnett 1979; Irwin 1986; Mitchell 1990; Card 1994a&b, 1995b). Care must be taken to ensure that both members of a prospective pair belong to the same race. There appear to be no obviously external differences between the sexes, other than the larger head size of males referred to above. A number of authors testify to the aggressive nature of this species in captivity (e.g. Longley I ':147; Johnson 1976; Delean 1981). In smaIJ enclosures larger specimens will eventually attack and injure any smaller room mates. Animals of similar sizes should be introduced to each other in spring and the male removed as soon as copulatory behaviour ceases. In large enclosures groups of animals can be kept together safely. Irwin (1986) kept five adults together in an enclosure with 7Rm 2 of floor space. They do well on a diet of small lizards, mammals and birds supplemented with large insects, vitamins and minerals. In captivity 7R
\
Little Book of Monitor Lizard s several clutches of eggs may be laid in a year, which hatch after 169- 265 days. at 29-32°C. Youngsters will immediately accept lizards and small mammals as well as insects. They grow rapidly and should be hou sed separately. Garret & Card (1993) record that newly-hatched individuals respond more to the smell of crickets than to the smell of mice and geckoes. A specimen at the Dallas Zoo survived for over 18 years in captivity (Snider & Bowler 1992).
VARANVS GIGANTEVS Gray 1845 Perentie The perentie is the king of the Australian goannas. It is the largest lizard on the continent and one of the most beautiful animals in the world. It was once thought to be an uncommon creature but in recent years the number of sightings has greatl y increased and the known range of the species has expanded. Despite their large size perenties are extremely shy and wary animals. Their pattern provides excellent camouflage and it is quite possible to walk within a meu'e or so of a large adult without ever being aware of its presence. Because of their ability to live undetected it is not clear whether perenties have expanded their range in the last few decades (see below) or whether they have succeeded in remaining unnoticed in many areas until recently. The perentie is found in arid areas of all mainland Australian states except Victoria and inhabits many islands off the western coast (Storr 1980). It is absent from the east coast and the tropical forests of the north , with northern and southern limits at about 18° and 30° longitude (Gow 1981 a; Storr 1980; Houston 1978). They are said to be particularly common on Barrow Island off Western Australia (Smith 1976; King, el at 1989). The maximum size of the perentie is probably not as great as many authors claim. King & Green (19lJ3) provide a useful discussion of size in this species. Stirling (1912) suggested a maximum size of almost 230cm. The longest found on Barrow Island by King el at (1989) had a total length of 196cm (88cm SVL) and the heaviest weighed 11.7kg. Butler (1970) record s a specimen of 17kg with a total length of 193cm from the same island. Stokes (1846) records that two specimens collected on Barrow Island in 1840 had total lengths of 213cm. Strimple (I <}88) suggested that one of these animals was the type specimen used by Gray, which has a total length of only 202cm (Mertens 1958). Many perenties do not grow to such an enormous size, and the specimens on Barrow Island may grow larger than the mainJand population (Case & Schwaner 1993). The limited data available suggests that females reach a smaller max.imum size than males, rarely exceeding 140cm TL. Bredl (1987) record s males of IXO and IlJOcm TL, and a female of 130cm TL. A male kept for 14 years in captivity had a total length of 135cm and weighed 2.9kg, whilst a female kept for seven years measured 116cm TL and weighed 1.55kg (Banks, pers.comm.). A specimen I saw in the Great Victoria de sert measured 52cm SVL (l23cm TL) and weighed 1.8kg when its stomach was empty. It appears that perenties approaching 200cm in length are the exception rather than the rule, and that in general few specimens grow larger than 150cm. If specimens of 240cm or more have ever existed, none seem to have survived to the present. Perenties are associated with desert regions and partic ularly with rock outcrops. However they are also found on grasslands and shrublands devoid of exposed rock. Where caves and crevices are available the perenties will use them for shelter, otherwise they take refuge ill burrows. Pianka (I <}<}4 ) suggests that the spread of rabbits through the interior of Australia may have enabled the perenties to occupy many areas that were previously unable to support 80
Monitors of the World them. The perenties cel1ainly prey on mammals to a greater extent than any other Australian monitor lizard. Stirling (1912) and McPhee (1959) both record that they are able to kill kangaroos and dismember those that are too large to be swallowed whole with the powerful forelimbs and claws. Lizards probably account for most of their food. especially large and dwarf goannas including weaker members of the same species (Pianka 1994). They are al so recorded as having eaten skinks. agamids, seagulls, orthopterans, centipedes and chilopods and are known to dig up the eggs and young of turtles from sandy beaches (Losos & Greene 1988; Green et al 1988, James, Losos & King 1992; Butler 1970). Much of the perenties' prey may be caught in open pursuit; they are reported to catch gulls by hiding under vehicles until the birds come close enough to allow them to be chased down before they can take to the air (Losos & Greene 1988; King et al 1989). Prey is usually killed by violent shaking. Horn & Visser (1988) suggest that perenties and sand goannas rarely occur in the same area, with sand goannas occupying open areas in contrast to the rock outcrops favoured by perenties. However a perentie we found on a flat spinifex plain in the Great Victoria Desert had swallowed a desert sand goanna almost the same length as itself and weighing about a quarter as much as its predator (pianka 1994; Bennett in press). Stirling (1912) records that perenties will mistake stationary people or horses for trees and climb up them in their attempts to escape. This behaviour has been observed many times (e.g. Pianka 1994b, Bennett in press). Perenties do not appear to be active throughout the year. According to Stirling (1912) they are inactive from May to August and pairs of animals may share the same burrow. This is confinned by Hom & Visser (1988) who found a pair of perenties in a cave at the beginning of October. Pianka (1982) found a large specimen in a burrow I m deep which he believed had been underground for at least a week . Perenties are extremely wary animals in the desert, although on Barrow Island they are said to be accustomed to people and relatively easy to observe. When threatened they often remain motionless, either in a stiff, extended pose (Bustard 1970) or lying flat on the ground (Swanson 1976; Hom & Visser 1988). They do not appear to adopt a bipedal stance for defence, but when running may take to the back legs for short periods (Stirling 1(12). Barrett (1950) published a picture of two perenties engaged in bipedal ritual combat. Similar photographs by Waite (1929) attributed to V.giganteus are actually of V.spenceri (Horn 1981). When chased perenties will seek refuge in trees, fallen logs, burrows or even in water (Pianka 1982; Hom & Visser 1988). According to Cogger (in Strimple 1988) they adopt an arboreal existence in some parts of Western Australia. Between September and June perenties are only active in early morning and late afternoon in Western Australia (Heger & Heger 1993). A similar bimodal activity pattern has been observed during the summer on Barrow Island (King, Green & Butler 1989). Perenties maintain active body temperatures of 33-39DC and can drop to 27°C at night (pianka 1982; King et al 1989). Breeding is said to occur in the spring (September - October) (Hom & Visser 1988) or summer (November to January) (Heger & Heger 1993). On Barrow Island mating occurs in Spring and hatchlings appear the following November (King et al 1989, Butler 1970). Here, activity ranges over ten days of up to 0.2km2 have been recorded and the same specimen has been found at locations over 5km apart. In the desert the lizards are likely to Cover much larger areas. I followed perentie tracks made in one afternoon and the early part of the next morning which extended over 2.5km. Pianka (1982) reports that tracks often exceed I km. They are able to accumulate large fat reserves. Stirling (1912) reports that an adult that died after a three month fast still
III
Litlle Book of Monitor Lizards weigh ed 7.7kg and contained fat bodies weighing almost Ikg. Details of metabolism are )!iven by Thompson (1995). Perenties have been rnainwined at a number of zoos in the Northern Hemisphere, but captive re production has only been achieved in outdoor enclosures in Australia (Bredl 1987 & pers.comrn: Bredl & Horn 19~7). Up to four adult specimens can be housed in an enclosure with 150m 2 of noor space. The substrate should allow the lizards to dig and large rocks provided to help them feel secure. Males may be very intolerant of each other but once compatibility between pairs has been established they may live together for many years without any violent incidents. However, perenties practise cannibalism regularly in the wild and care must be taken that only animals of compatible sizes are housed together. Mating and cgglaying occur in late spring and early summer. Up to II eggs, each weighing around 80g, are laid in a single clutch, which hatch after about 8 months at 30-32OC with 85% humidity. Hatchlings weigh 30-50g and measure 14.5-15.5cm SVL (37-38cm TL). If incubated with higher humidity they would doubtless weigh more. After a month they increase in weight by ahout 5()%. They should be fed a mixed diet of reptiles, birds, mammals, freshwater fish and large insects, together with vitamin and mineral supplements. A short period of inactivity during the winter is probably beneficial . Green et al (19R6) estimated that during the summer, when food is abundant (in this case baby turtles containing about 3kJ of energy per gramme of body weight), adults eat about 36g of prey per kg of body weight, using II RkJ of energy per kg per day to sustain themselves. During another summer when food was less abundant they used only about 57kJ per kg per day and consumed 7.3g of food per kg per day. Perenties have survived in captivity for almost 20 years (Snider & Bowler 1992).
VA RA NUS GILLENI Lucas & Frost H195. (iillen's goanna, Mulga monitor. Gillen's goanna is found throughout the arid interior of Australia : in Western Australia, Northern Territory, Queensland and South Australia. As its common narne implies it is often found in areas of dense mulga (A cacia) but also inhabits more open deserts of spinifex and Eucalyptus (Cogger 1962; Thompson & Hosmer 1963; Pianka 1969; Delean 1980). It normally reaches a length of about 40cm (lRcm SVL) but Green and King (\993) give its total length as 7Ocm. Mean weight of 4 examined by Bickler & Anderson (1986) was 30g. Bustard (1970) reports that tail is somewhat prehensile and may be used to grip branches whilst descending. The mulga monitor shelters in trees but catches a lot of its food on the ground . It probably has the most diverse diet of any of the dwarf desert goannas. Spiders, orthopterans, beetles and other lizards are its usual prey, but they also eat larger items such as birds eggs and small mammals as well as animals the size of an ant. In captivity they will also accept fish (Pianka 19()9; Barnett 19R I; Losos & Greene 1988; James, Losos & [(jng 1992). Like other dwarf goannas the mulga monitor often eats the tails of geckoes that it is unable to catch and/or swallow. They are usually found under bark or in tree hollows. Little is known of its beh aviour in the wild but i t~ diet indicates that it forages for food and investigates the daytime retreat~ of a number of terrestrial and arboreal geckoes. Active body temperatures of ~ () .4-:1X.4°C have been recorded. Associations of large numbers of mulga monitors have been
!!2
Monitors of the World found together but it is uncertain whether they always live together or congregate for the breeding season (Greer 1989). In many areas they are uncommon. Females may contain eggs at any time except the late summer and early winter and may lay more than one clutch per year. Clutches of up to seven eggs have been reported which. in captivity at least, hatch after about 3 months. Eggs may be laid at the end of a 30cm deep burrow. and the entrance may be sealed with sand (Pianka 1969; James. Losos & King 1992; Sclunida 1985). Ritual fighting has been described several times, and even occurs between juveniles (Murphy & MitcheU 1974; Carpenter et at 1976; Hom 1985). The animals lie belly to belly, embracing each other at the shoulders and the pelvis and attempt to flip each other over. BickJer & Anderson (1986) studied the rate of oxygen consumption in v'gi/leni and found that they were unable to exhaust specimens on treadmills running at I km per hour. Even after "many minutes" they were able to run without building up any oxygen debt. At rest they use just .2m1 of oxygen per gramme per hour, this figure rises almost 30 fold during energetic exercise. Rates of water loss in Gillen's goanna is half that of other Australian varanids studied (0.06mg of water per cm 2 of skin per hour at 30°c) (Green & King 1993). The mulga monitor has reproduced in captivity on at least several occasions (Horn 1978; Gow 1982; Boyle & Lamoreaux 1983; Broer & Horn 1985; Eidenmuller 1994. Husband. pers.comm.). The animals can be sexed by the presence of spines on either side of the vent in males. An enclosure with a floor area of I m2 is sufficient to house a pair. It should be furnished in the manner typical for desert monitors with plenty of branches and shelters above the ground. Temperature and photoperiod should fluctuate seasonally and diet should reflect the variety of animals taken in the wild. Ambient temperatures of 20-30oC (I6-24OC during winter) are suitable. Eggs incubated between 27-30 oC hatch after 89- 104 days. Hatchlings weigh 2-3g and measure 12-I4cm (5-6cm SVL).
VARANUS GLAUERTI Mertens 1957 Glauert's goanna Glauert's goanna is an elegant, rock-dwelling lizard with a very long tail and long limbs. Mertens described it from two specimens previously assigned to v'timorensis similis. This beautiful goanna is found only in the extreme north of Western Australia and the Northern Territory, and also 'ti occurs on a number of islands off the coast (Storr 1980; Rankin et at 1987; Rokylle 1989). Rankin et at (1987) note that they are found in the highest parts of Amhemland. Western specimens often have an ocellated pattern on the back, whilst those from further east have a barred pattern. Those from the south parts of the range in Western Australia tend to have more yellow colouration than those from the north. Hatchlings are said to be extraordinarily beautiful animals with very bright blue colouration (Green & King 1993). They reach a total length of about 80cm. of which only about 30cm is head and body. The tail varies between 183-268% of the SVL. Average SVL of 31 specimens examined by James et at (1992) was 19.8cm. A captive specimen at least seven years old weighed 165g (Hodge pers.comm.). Glauert's goanna inhabits dry rocky areas and has been seen foraging in leaf litter amongst boulders (Rankin et at 1987). Rokylle (1989) saw them foraging on vertical rock faces. in ground vegetation and on trees and reports that wild specimens accustomed to humanity will even forage on people if they remain still. Losos & Greene found that orthopterans and
113
Little Book of Monitor Lizards spiders were the major prey. along with roaches. caterpillars, lizards and their eggs. James el (// ( 19Y2) I:onsidered that lizards (geckoes and skinks), orthopterans and spiders were their major foods . Virtually nothing is known of the reproductive biology of this species; James el (// ( 19<)2) suggest th at eggs are laid at the end of the dry season and beginning of the rainy season (November to January). Clutch size and length at sexual maturity are unknown but they rel:orcied a female of I (,5mm S VL which contained three eggs. I Gin find no rel:o rds of this species reproducing in captivity. Males can be distinguished by the. presence of enlarged and raised (but not spiny) scales on either side of the tail base. In captivity the species likes to burrow and can be kept with agamids and skinks of a similar size. In sects. small mammals and other lizards are probably suitable foods. They show a liking for tomato in captivity (Hodge. pers. comm.).
VARANUS GLEBOPALMA Twilight goanna.
Mitchell 1955.
The twilight goanna is another long-tailed rock-dwelling species. It has u much larger distribution than Glauert's goanna. inhabiting the far north of Western Australia, Northern Territory and Queensland but is absent from the Cape York Peninsula. They also inhabit a number of islands off the northern coast. V.Rlehopalma is one of the most intriguing of the goannas. They are said to be common in many areas but are rarely seen (e.g. Sl:hmida 19R5; Gow 19R I). The scientific name of this species refers to the shiny black pads found on the underside of the feet (Chapter 4). Its common name is derived from its habit of foraging after sunset, a unique behaviour among varanids (Christian 1977 , Shea et al 19R8). Although there are records of other species being active occasionally at night (e.g. Auffenberg 1981 for V.komodoensis; Gaulke 1992a for V.salvator) none seem to move regularly during the hours of darkness. The twilight monitor is not exclusively crepuscular and I:an be sighted throughout the day (Valentic 1988). The twilight goanna reaches a total length of just over IOOcm (Storr 1980). The tail is 179 24()% of the SVL. Average SVL of 43 specimens examined by James et al (1992) was 27.4l:m, maximum 34.3cm. They probably attain sexual maturity at around 17cm SVL. Horn & Sl:hurer (1978) suggest that western specimens have longer tails than those from the east. They can be easily distinguished from V.glauerti by the lack of bright bands on the tail, although in very young specimens of V.glebop/ama the tail may be completely banded (see Horn & Schurer 1978) adults usually have plain tail tips . Colouration and amount of pattern varies widely, presumably depending on habitat The twilight goanna inhabits areas of rock escarpment and large populations may be found in small areas (Christian 1977). Rokylle (1989) considered them to be more common on rocky hillsides with spinifex growth than on the rock outcrops themselves. They are reported to shelter in narrow rock crevices and lie in wait for food on elevated rocks, pouncing on their prey as it passes (Horn & Schurer 1978). All authors comment on the extreme shyness of this species. They react to movement as far as 50m away by dashing for shelter under rocks. A Ithough they I:an climb vertical rock faces they may be less adept at this than Glauert's goa nna (Rokylle 19R9). Valenti c (I 994} reports seeing a twilight goanna chase an agamid R4
Monitors of the World over 30 metres of rocky landscape before catching and consuming it. He estimated a speed of over 20kIn per hour. Horn & Schurer (1978) speculated that this goanna may feed largely on other lizards. This has been confinned by analysis of stomach contents of museum specimens (Losos & Greene 19BB; James el al 1992) and by Valentic's observation. Twilight goannas feed mainly on lizards (pygopods, skinks, agamids and varanids (including V.glaueni) and frogs. They also take orthopterans, spiders and centipedes. Breeding probably occurs towards the end of the dry season and the beginning of the wet season (October - January). At least 5 eggs are produced. In captivity this species is extremely timid and shy. They will accept insects, frogs, lizards and small mammals. Unfortunately I can find no records of captive reproduction. Males are encountered more frequently than females and can be distinguished by the presence of enlarged scales on' either side of the tail base. Basking behaviour is unknown but there are suggestions that this species does not appreciate the very high basking temperatures enjoyed by most other monitor lizards. A large enclosure, furnished with plenty of rocks and stones to provide numerous hiding places, is required to help the animals feel secure. Ideally their diet should contain a mixture of insects and other lizards. Horn & Schurer (1978) report that some individuals refuse to eat mammaJs.
VARANUS GOUWII (See notes on taxonomy under V.flavirufus) Gould's goanna Varanus panoptes panoptes - Varanus gouldii gouldii Grey 1838 Varanus panoptes rubidus = Varanus gouldii rubidus Storr 1980. • Varanus gouldii horni Varanus panoptes horni Bohme 1988 Gould's goanna is one of the largest Australian goannas, but because of the confusion regarding its taxonomy (see under V flavirufus) it remains very poorly known, despite the fact that there are plenty of accounts devoted to it in the literaturel
~
At present three subspecies are recognised; V.gouldii gouldii inhabits the extreme north of eastern Western Australia and the Northern Territory, the islands of the Torres Straits and probably many other islands off the northern coast and V.gouldii horni is found in southern New Guinea. Records of Varanus gouldii on the islands of the Torres Straits and many other islands off the northern coast probably represent V.gouldii, but it is unclear whether they show more resemblance to Vg.gouldii or V.g.horni. An isolated race. V.gouldii rubidus, exists in central Western Australia. Animals from the north of Australia and New Guinea have a banded tail tip and more midbody scale rows than V flavirufus (192 242 vs. 132-189). The animals from New Guinea have 170-205 midbody scale rows, but otherwise there do not appear to be any distinguishing morphological chara(;ters. Vg .rubidus has a plain tail tip and mainland forms have 195-223 midbody scale rows. Island populations (i.e. from Dolphin Island) have as few as 176 scales rows. In pattern V.gouldii differs from V flavirufus by possessing well defined pale and dark spots, usually arranged in rows over the ba(;k (Storr 1980; Bohme 1988).
85
Monitors of the World The r~nge of this species may be much greater than is suggested by the current literature. Schmina (19115) notes that specimens of "V.gouldii" in the Sydney sannstone region are narkly colouren with ten rows of yellow spots on the back and have a banded tail tip. At present the niagnostic char~cteristics used to distinguish between V.gouldii and V flavirufus no not appear to be 100% reliable. Comparisons of animals from throughout Australia, both from a morphological ann biochemical perspective, are needed before the taxonomy of this group can be revised satisfactorily. Some anditional information on this group of monitors call be founn in Grunnke & Grundke (IlJ92b). Gould's goanna is a mighty lizard. They are heavily built, powerful and fearless creatures that often anopt a bipeelal stance, either in response to a threat or to gain a better vantage point (e.g. Barbour IlJ43). They have very powerful front limbs and frequent areas of tightly pal.:keel sann ~nd clay. Virtually nothing is known of the way of life of the New Guinea subspecies gouldii horni. Bohme (191111) suggest a maximum size of at least 140cm 11., and records the following locations; Teluk Berau, Gelib, Maerauke, Koerik, Bensbach, Port Moresby, Aroma and Yule Island and suggests that they may be found throughout the grasslands of southern New Guinea. Whitaker ('I al (19112) record it only from Western ann Central Province in Papua New Gui nea. Parker (1970) claims that this lizard was once common around Port Moresby hllt latterly surviveel only on a few nearby islands (including Loloata and Motupuri). In the north of Australia V.g.gouldii appears to be particularly associated with the vicinity of rivers. Shine (19I1fi) rarely found them more than 200m from water and Stammer (1970) is probably referring to Gouin's goanna when he describes the river goanna, which digs holes in the banks of dry rivers ann creeks. Similarly Cogger's (1981) report that a race in Arhemland inhabit mangroves, tidal flats, floodplains and sandstone escarpments may well refer to V.gouldii. Around Jabiru in the Northern Territory their usual foods are small mammals, other reptiles (skinks, agamids, varanids and snakes) and their eggs, frogs, crabs and birds, as well as the obligatory orthopterans and lepidopterans. They have also been seen to I.:ongregate around fish kills. Wilson (1987) photographed a specimen digging up tortoise eggs besides a small river in Western Australia. Koch (1970) records that V.gouldii eats large scorpions. Around Jaribu adult males can attain weights as great as 4000g and reach lengths of up to fi7cm SVL. In contrast females tend to weigh only one-third as much as males and none larger than 43cm SVL were found. Up to 13 eggs may be laid in a single clutch. Most breeciing probably occurs during the wet season; presumed courtship was seen in July (Shine 19Xfi). Hatchlings measure about lO.5cm SVL. Little is known of the ecology of V.gouldii robidus. Bodies of water are absent from most of its range. Like the nominate race they appear to favour harder substrates than Gould's goanna. At Wanjarri, an abandoned cattle station in Western Australia, they dig deep (130cm) burrows in ground packed rock-hard by thousands of hooves. When I visited in 19lJO a drought had caused a mass die-off of kangaroos and the ground was littered with corpses in various states of decay and large numbers of kangaroos on the verge of death. Bloateel Gould's goannas were feasting on the flesh of a particularly foul, putrid smelling and maggot-ridden corpse, tearing off chunks of rotten flesh with the forelimbs and devouring them with apparent delight The largest V.g. rubidus recorded by Storr (1980) measured Opposite: Horn's monitor, Port Moresby, New Guinea (Romulus Whitaker) llfi
sprezl1
Ul
.I01lUOIN )0 )fOOt! ;}\11 11
Lillie Book of Monitor Lizards S()~111 SVL (I :l7l:m TL). The largest specimen at Wanjarri mea~ured 64cm SVL (I 55cm TL) and weighed over 5()()()g. Its swollen belly must have contained at least a kilo of festering meal. In comparison another specimen of 56cm SVL (135cm TL) weighed only 1750g. It wa s extremely thin and may have been attracted to the area from afar by the smell of decay. Bipedal ritual combat is said to occur between adults congregated around carrion (Bennett 1<)<)2). In this area Gould's goannas are absent from areas of softer sand.
The only report of captive breeding in this species is by Haninger·Berlin (1994). A pair were allowed to remain inactive in the dark at 16·18°C for three months of the year, separated for a month and then reunited, whereupon courtship,and mating occured within a month. A single c lutch of up to II eggs is produced which hatch after 210·229 days at 28°C. At cooler temperatures they can take up to 356 days to develop. Hatchlings measure about 30cm TL and weigh around 27g. These animals require spacious enclosures with plenty of hiding places.
VARANUS GRISEUS
Desert monitor, grey monitor
Varanus griseus griseus Daudin 1803 Grey monitor Varanus griseus caspius Eichwald 1831 Caspian monitor Varanus griseus koniecznyi Mertens 1942 Indian desert monitor Varallus Rriseus is one of the most widespread monitor lizards. It has an enormous range, occurring from the Sahara Desert through the Arabian Peninsul
VWiwus caspius has 5·8 bands on the back and 13·19 bands on the tail with a plain tail tip. The tail shows significant lateral compression and is 118·127% of SVL. There are about 143 rows of scales at midbody, Vwiseus koniecznyi has 3·5 bands on the back and 8·15 bands on the tail with a plain tail tip . Tail may show some lateral compression, but not to the elltent seen in V.griseus caspius. It is II X·I27 % of SVL. In addition its head is broader and flatter than that of V.griseus Wis('us. There are 108·139 rows of scales at midbody. His descriptions were based on a very small number of specimens and it is likely that this IUxonomy will be revised at some time in the future, hopefully using biochemical features rather than external ones. The desert monitor is an magnificent animal. It is my favourite monitor lizard for several reasons . It inhabits some of the most hostile regions of Earth, experiencing blistering heat in the summer and extreme ~old in the winter. Grey monitors are lizards with attitudes. They
RR
Monitors of the World are very spirited creatures which cannot be tamed and lhey appear to hate hwnanity wilh a vengeance. In turn, people generally hate the grey monitor and it is persecuted almost everywhere it is found. The energy and spirit of its lhreat display are doubtless responsible for lhe many sinister characters lhat are attributed to it by humanity. They are believed by many to be as venomous as any snake, and are also supposed to be capable of inflicting a variety of deforming, debilitating and tenninal illnesses on any unfortunate person lhey encounter. In fact lhe grey monitor is probably a benefit to humanity where it is aUowed to survive unmolested. They eat large numbers of crop-destroying beetles and larger specimens consume adult cobras and vipers wilh great relish. Its defensive posture is largely bluff and is only assumed if lhe animaI is cornered and unable to escape. In captivity lhe desert monitor is not particularly co-operative. They have been kept in captivity for over a century (Von Ralhgen 1894), but only a single captive breeding has been reliably reported. Our failure with lhe captive maintenance of lhis species is largely attributable to a lack of understanding about its way of life in lhe wild and in particular about its seasonal behaviour. The grey monitor V.griseus griseus occurs in lhe deserts of north Africa (from Morocco and Mauritania east to Egypt and Sudan), lhe Arabian Peninsula (allhough it appears to be absent from the island of Bahrain). soulh-eastern Turkey, Syria, Israel, Palestine, Lebanon, Jordan and Iraq (e.g. Haas 1951; Hass & Battersby 1959; Anderson 1969; Schmidt & Marx 1956, 1957; Schmidt 1919; Aktan 1971, Arnold 1984; Bishai 1960, Martens & Kock 1992). It reaches a maximum size of about 120cm 11. in Iraq (Khalaf 1959) and 100cm 11. in Israel, but in Algeria specimens of 80cm 11. are rare (Mammeir. pers. comm.). TolaJ size anained seems to depend on the climate of lhe area, wilh largest specimens coming from areas which yield more food or allow longer activity seasons. Mosauer (1934) noted lhat specimens from Tozeur and Nefta in Tunisia were smaller lhan those from Gafsa. The largest male found during a comprehensive study in lhe coaslaJ plains of Israel was 46cm SVL and 1,261 g, the largest female 38cm SVL and 702g (Slammer & Mendlessohn 1987). In captivity however lhey can attain weights in e)(cess of 3,OOOg. The tail varies between 120-150% of SVL. Details of scalation and morphology can be found in Mertens (1954). The pattern and colouration of lhis lizard shows great variability. In dry areas with little vegetation (e.g. the sand dunes of Mauritania) grey monitors may have no pattern at alJ, in wetter areas with more lu)(uriant plant growlh lhe animaJs can have very bright patterns. Juveniles are always brighter than lheir parents. In Israel grey monitors tend to avoid beaches and keep to more inJand areas. They inhabit sand dunes and are not adverse to areas of human activity including rubbish dumps and building sites (Stammer & Mendlessohn 1983, 1987). Anderson (1963) records lhem from as high as I ,200m above sea level and Arnold (1984) records lhem from a variety of substrates induding gravel in Arabia. In lhe Sahara desert lher inhabit alJ regions but are much more common in lhe more humid zones (about 6 per Ian) lhan in more arid areas (about 2 per lan2) (Vernet 1982). In lhe coastal plains of Israel Stanner & Mendlessohn found about 4 specimens per km2 . Perry & Drni'el (1995) note lhat lhe grey monitor has disappeared from many disturbed dune areas. Not surpisingly the diet of the grey monitor varies enormously depending on its habitat. Where other vertebrates are plentiful lhey tend to form the bulk of lheir prey. In Israel other lizards and snakes are lheir most common prey, along wilh ground-nesting birds, tortoise and the eggs of alJ lhese animals. They also prey on toads and mammals (including gerbils and young hares) and will take carrion including dead hedgehogs and cats (Stanner & 89
Little Book of Monitor Lizards Mendlessohn I IJR(). Invertebrnte prey are less important than in many other desen-dwelling monitor lizurds. but include beetles. orthopterans. heteropteran bugs. ants. snails. centipedes ;lIld scorpions. This wide variety of prey suggest that. like many monitor lizards. the grey lIlonitor devours any animal of a suitable size that it encounters. Diet in Algeria appears to be very similar (Vernet & Grenot IlI73). Seven stomachs of animals from a variety of locations examined by Losos & Greene (19RR) also contained lizards and snakes. Aktan (1971) found two brge lizards and pieces of eggshell in a specimen from Turkey. Lizards. snakes and mammals have also been recorded from the stomachs of animals in Arabia (Arnold 19R4. Tilhury IlIXXl. Egypt (Schmidt & Marl( 1957. 195R) and Tunisia (Mosauer 1934). Andres (llII14) rel:ords that adults will eat small puppies. The deserts inhabited by the grey monitor are subject to great vanatlOns in seasonal temperature. In Israel males are active from late April and early May until July or August whilst females remain active until late October or November (Stanner & Mendlessohn 19R3. IlJX7. IlIlI I). TIle lizards stick to well defined home ranges and those of males are much larger than those of females (about I km 2 compared with O.Jkm2). Females maintain the same home ranges for at least several years whilst males change theirs annually. Foraging distances of 2km or more are common. In Algeria the monitors have two periods of activity, from April to June and a shorter period during October. During the winter and hottest part of the summer they remain below ground. Horne ranges were estimated at 1-4km2 (much larger than those in Israel, presumably because of lower food densities) and foraging trips of up to 8km per day were recorded (Vernet 191<2: Vernet el al 1988a). These studies suggested that males were not particularly more active than females. In the same parts of Algeria Saint Girons & Saint Girons (1959) estimated home range size as 2-5km 2. Although the lizards have well defined home ranges they are neither territorial nor do they consistently use the same shelters and basking sites. In Syria grey monitors are found only in spring and early summer (Martens & Kock 1992) whilst in Mauritania active grey monitors have been seen as late as November (Linley. pers. comm.). In Algeria grey monitors maintain active body temperatures of between 35-38°e. At temperatures below 20°C the lizards become inactive and hibernation is induced at about 17"C. The lizards voluntarily allow body temperature to get no higher than 41°C and die at temperatures of between 44-47°C (Vernet et at 1988b). Grenot (1968) (reviewed in George ( IlIX())) found that the grey monitor is able to maintain a body temperature of 42°C for up to four hours at an ambient temperature of 50°e. In warm weather the lizards can raise their body temperatures by as much as 0.5 0 C per minute by basking (Francaz et at 1976, 1978). Although the seasonal activity of the grey monitor depends largely on temperature, Vernet et al (llIXHa) believed that the daily activity of the lizards depended more on prey availability than climate (similar findings have been reported for V.atbigularis). Lemire & Vernet (1985) report that the grey monitor has salt glands which allow it to minimise water loss (see Chapter 3). In Israel grey monitor burrows are said to be an average of 125cm long and just 30cm deep. They vary greatly in shape (Stanner 1985). These burrows are probably used only during the wanner part of the year. During the winter the lizards may take shelter in much deeper refuges. An Algeria they have been recorded from burrows as deep as 300cm (Marnmeir,. rers. comm.). Schmidt & Marl( (1957) record that in Egypt grey monitors dig very deep and 90
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Little Book of Monitor Lizards complex burrows with several openings. Andres (1904) re{;ords that a captive spe{;imen escaped by digging a very deep burrow under a garden wall. Little is known about the breeding behaviour of the grey monitor lizard. In AJgeria, Tunisia and Israe l mating occurs during May and June and eggs are laid in June and July (Vernet, Lemire & Grenot 1983; Mertens 1942; Stanner 1985). There are no records of nesting sites. In Israel females' weight may be reduced by as much as 47% after egg laying. Their continued activity into the early winter is probably due to their need to accumulate large fat reserves both to maintain them through the long period of inactivity and to provide energy to fonn eggs for the next breeding seaso n. Hatchlings appear in March of the following year, but an incubation period of eight months seems unlikely (see below). The habits of the juveniles remain completely unknown. Thilen.ius (1897) suggests that females may return to the nest site after oviposition, but makes no attempt to explain why. The Caspian monitor (V.griseus caspius) is the largest race of the desert monitor. It is considered to be in danger of extinction and is one of the few monitor lizards whose commercial trade is completely outlawed. Despite this they are regularly offered for sale and, a few years ago at least, were not an uncommon sigh t in Moscow's pet market. The Caspian monitor is found from the east coast of the Caspian Sea tllroughout the deserts of central Asia (including many islands of the Aral Sea as far as about 690 east and 460 north. In the south it is found at elevations of up to 800m in the Kopet Dag mountains and extends into northern Iran, western and sout hern Nghanistan as far as western Pakistan. It is best known from the states fonneriy affiliated to the U.S.S.R.; Turkmenistan, Khazak stan, Uzebelcistan, Kirgizstan and Tadzikistan. It previously occu rred in the Fergana Baisin but is now extinct there and has also disappeared from the Golodnaya and Dalverzinskaya regions of Uzebekistan (Leviton & Anderson 1970; Yadgarov 1968, el al 1988; Ataev 1987; Shammakov 1981; Makayev 1982). Specimens have also been recorded from as far east as Tasi1kent (Kulagin in Nikolskii (1915)) but they do not occur there now. The Caspian monitor reaches a maximum size of about 140cm. Males tend to be longer than females (largest male recorded from Turkmenistan by Shammakov (1981) was 58. Scm SVL, largest female was 46cm) but not much hea vier (heaviest male was 2,850g heaviest female 2,700g). The Caspian monitor is di stingui shed from other races of V.griseus largely by the shape of its tail, which is laterally compressed in contrast to the tails of other races, which tend to be more or less rounded in cross sec tion. The Caspian monitor is found in both sandy and clay deserts. They avoid areas of dense vegetation but are found in sparse woodland. Those from clayey areas are often a distinctive reddish colour (Bennett 1992a). On Islands in the Aral Sea they are found in salt marshes as well as sandy areas. They are sometimes found on the edges of agricultural land, but, because they are often killed when encountered, Caspian monitors tend to be very uncommon in areas of human habitation. In abandoned settlements they often inhabit cracks in wattle and daub houses. Caspian monitor li zards reach their highest densities where colonies of mammals are abundant. Makeyev (19!)2) reco rds 9-12 spe{;imens per km 2 on the edge of Karabil, close to Karamet-Niyaz (Turkmenistan) and in the Saihan Valley (Uzbekistan), 5 spe{;imens per km 2 in southeastern Turkmenistan and 3-5 specimens per km 2 on clay desert at Kara-Kala. Over most of the sandy desert densities are estimated at 2-3 lizards per krn 2, whilst in river valleys numbers drop 10 I-I.S specimens per km 2
92
Monitors of the World The diet of the Caspian monitor is similar to that of the nominate race. In many areas they feed on hatchling tortoises which emerge in the spring and excavate and consume tortoise eggs which are laid in May. They also eat small mammals. including the giant gerbil and young hares. In Turkmenistan adults prey extensively on large snakes, cobras and vipers up to l4()cm are swallowed whole. Shammakov (1981) lists 10 species of lizards, six snakes, four birds and six manunals that are regularly eaten by the monitor lizards. In Kyzulkhum their diet consists mainly of rodents (especially the giant gerbil) and far fewer numbers of lizards and invertebrates than are consumed in the Karakhum. In the former area the lizards regularly enter burrows in search of rnanunalian prey, whilst in the latter region they tend to forage mainly on the surface (TseUarius et at 1991). In the Surhandarja Baisin they feed largely on young tortoise, small mammals and invertebrates (especiaUy tenebrionid beetles) (Yadgarov 1968). Caspian monitors will also prey on srnaUer members of their own species (Makarov 1985). The lizards ability to prey on snakes that are extremely dangerous to man is particularly interesting. Experiments to detennine the Caspian monitors' ability to tolerate viper and cobra venom by injecting them with venom sufficient to kill up to 4,000 adults humans seem to indicate that the lizards have considerable resistance to both haemotoxic and neurotoxic venoms (Rjumin 1968). In Turkmenistan Caspian monitors commence activity in late March and early April. Like other desert monitors they are active during the middle of the day in spring, but as temperatures rise they adopt a bimodal activity panern, foraging early in the morning and late in the afternoon but spending the hottest part of the day below ground. By September and October temperatures are cool enough for them to resume a single period of activity, but they commence hibernation earlier than most other lizards and have virtually disappeared by early October (Shammakov 1981). Activity temperatures of 31.7 -4().6°C have been recorded (Sokolov et at 1975; Tsellarius et at 1991). The Caspian monitor is capable of running at speeds of up to 20km per hour over short (I OO-150m) distances. Home ranges of over Ikm 2 have been detennined for adults (Tsellarius et at 1991). The same study suggested that Caspian monitors may mark their territory in spring and early summer, in contrast to the work of Stanner in Israel which found no evidence of scent marking·. Foraging trips may ex tend to over IOkm per da y (TseUari us & Cherlin 1991). Caspian monitors are strong diggers. In clay desert where the substrate is too hard to excavate they shelter in mammal burrows and in river Valleys they often utilise the burrows of ground dwelling birds. In sandy desert burrows are often more than 500cm long and typically 50-12Ocm deep. Burrows used during the spring and summer tend to be in more open areas than those used for hibernation, which are dug under bushes Yadgarov 1968; Makayev 1982; Bennett I 992b). Mating occurs during April and May. Up to 34 eggs are laid in a burrow 70 II4cm deep usually situated on a slope during June and July. Sometimes the burrows of rodents are used as nesting sites. Females spend up to a week digging test holes and preparing nests, guard the eggs for several weeks after egglaying and have been reported to return to the vicinity of their eggs around hatching time. The eggs hatch in September or O!.:tober but the youngsters remain together in the nest and do not commence activity until the following spring. Eggs laid in captivity weigh 32-35g (Yadgarov 1968; Shammakov 1981; Tsellarius & Menshikov 1995; Dujsebayeva 1995; Makayev. pers.comm; Kudryatsev
•A very exciting and detailed account of this behaviour can be found in Tsellarius & Menshikov (1994). 93
Little Book of Monitor Lizards rers. comm.). Sexual maturity is attained within three years (Shammakov 1981). Tsselarius and Cherlin (Il)l) I) note that many Caspian monitors have scars on the back, which they
Monitors of the World monitor (in which the lizard seized a flllger and chewed on it for a minute) the "victim" suffered dizziness, muscular aches and pains, accelerated hearbeat and had difficulty breathing through the mouth. After 24 hours however all symptoms had disappeared . According to Gorelov (1971) injections of saliva from Caspian monitors causes momentary paralysis when injected into small birds and rodents. This however is refuted by Auffenberg (I ':IXfi) who claims that the salivary glands of desert monitors have no such properties. The desert monitor has been attributed with much more malevolent powers. According to Bogdanov (in Nicolskii 1915) if a desert monitor runs between a man's legs it can rob him of his sexual prowess and render him impotent. Its common name amongst the I(jrgizes, kasal, means illness and is derived from this tenifying superstition . In Algeria their ability to survive the bites of venomous snakes is supposed to be due to their habit of seeking Ollt and consuming plants which act as antidotes against the venom (Mammir, pers. comm.). In Turkey the desert monitor is known as zagar, or gomgomok. In Iraq it is urqhal. In Turkmenistan the Caspian monitor is known as zemzem and in Tadjikistan as ichke mere. lY';"'1>
VARANVS INDlCVS
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Mangrove monitor Varanus indicus indicus Mangrove monitor . Varanus indicus kalabeck Kalabeck monitor Varanus indicus spinulosus (;eorge's Island monitor
Daudin
1802
Lesson
1802
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Mertens 1941
The mangrove monitor is a large active lizard with an enormous distribution. Its scientific name is misleading because the species does not occur in India, or anywhere near it. Mangrove monitors are found from northern Australia and New Guinea east to the Solomon Islands, Marshall Islands, Caroline Islands and Marianas Islands. Its distribution through mllch of Micronesia remains uncertain. Luxmoore et al (I ':188) give the following locations: Micronesia (Kosrae, Mortlock, Woleai, Ifalak, Yap, Ulithi and several islands in the Truk Atoll), Guam, Indonesia (eastern sector: Irian Jaya and adjacent islands. north to the Talaud Group and west to Halmahera and the Moluccas (Ambon, Buru, Ceram ell':.) and Timor, Marshall Islands, Palau (Ngeaur, Oreor, Babeldaob (Babelthaup) Ncheangel (Kayangel) and Solomon Islands (Guadalcanal, Isabel, Malaita and San Christobal). In Australia they are found only in the extreme north; Arnhemland and especially Cape York, Queensland. Reports of V.illdicus in Sulawesi appear to be incorrect (Indraganeali, pers. comm.) but they may exist on Obi or Halmahera in broad sympatry with V.saivator. Additional location data can be found in Peters & Doria (1878), Hediger (1':134), McCoy (19XO); Heatwole (1':175), Fisher (ll)4H), Brandenberg (1983); Mertens (1958) and Burt & Burt (1':132). Within this massive range there is a huge amount of variation in size, pattern and scalation and major revision of the group is underway. A previously unknown species from New Britain. V.dorellllL/s. has been recently rediscovered (Bohme, Horn & Zeigler 1'1':14). The V.i,uJicu.l' group represent a taxonomist's paradise, providing he or she does not get sea-sick. V.illdicus kaillh('cJ.: (from the Waigeu Islands off New Guinea) has small widely spal:ed scales on the neck and was not considered a valid subspecies by Brandenberg (ll)X3 J. Bohme (I <)'1 I) notes that the type specimen of V.i.J.:aillhecJ.: is lost and sUPflorts Brandenberg's view
95
Little Book of Monitor Lizards Ihal the animals on Waigeu are typical mangrove monitors. Live "Kalabeck's monitor" are advntised by animal dealers in North America, but as far as I can ascertain these animals are Jctually V.d"I"('o/l/ls. V.i"rlicll.\· .I(1inu/oJuJ has a shorter, bulkier snout than the typical mangrove monitor and is further distinguished by its spiny scales on the back and neck and nostrils which are situated clo~ e r to the tip of the snout than in the nominate race. They are dark in colour, with large dirty-yellow spots over the back. Only one specimen, collected in 1897 on George's Island in thr Solomons. was known to science until live specimens were imported to the U.S.A. in the I')XOs. These animals are said to come from forests on the larger neighbouring Ysabel Island, where typical mangrove monitors are also found. On this basis Sprackland (1993. 1994) cOllsiders it a separate species.
The mangrove monitor attains different sizes in different parts of its range. Swanson's (1976) cbim that they reach 200em TL is probably an overestimate. Schmid a (1985) claim~ they reach 150em TL and Cogger (1981) gives a total length of 100cm for Australian specimens. III the Solomon islands they average 50cm SVL (125cm TL). The largest from New Britain examined by Hediger (1934) was 124cm TL. On islands and cays of eastern New Guinea they reach I(){)cm TL whilst on Ceram they reach almost 140em TL (Edgar, pers. comm.). The largest from Lego. northern Papua, was 34cm SVL (Room 1974). The largest found on Guam by Wikramanayake & Dryden (191111) were 58cm (male) and 44cm (female) SVL with wrights of IlIOOg and 500g respectively. Whether such great size differences between the sexes exist throughout the range is not yet certain, but seems likely. Mangrove monitors are always found close to water. In northern Australia they are restricted t!1 mangroves (Cogger 1911 I) and in New Guinea they are never found far from the coast. In
the Yap group they were found in forests and swamps (Fisher 19411). In the Solomons they are said to prefer more open areas to thick forest and to be common in coconut plantations (McCoy IlIXO). In mangrove swamps they prey largely on crabs (Dryden 1965, Uchida 1967, McCoy IlIXO). They also take small mammals, snails, birds and their eggs, other lizards, the eggs and young of turtles and crocodiles. slugs, worms and a variety of insects (Tanner 1951; Swanson Inti; Webb el at 1977. Dryden & Taylor 1969, Losos & Greene 1988). In captivity they prey avidly on fish and these are probabLy taken in the wild where conditions permit. Traeholt (1993) noted that water monitors appeared unabLe to catch fish in deep water. but mangrove monitors appear to have no such problems and in captivity have been known to polish off large (and e)(pensive) shoals of rainbowfish in just a few hours (Behler, pers.comm.). The fact that prey animals are taken from underwater, on and below the ground and from trees testifies to the ubiquitous behaviour of this monitor lizard. They swim and dive as well as any other goanna, can climb with great agility, leap from high trees or rocks and can dig proficiently (Hediger 1943, Bustard 1970). In some areas they spend most of their time in the water. either resting or looking for food, whilst elsewhere they are more terrestrial in habit. Similarly in many areas they will take refuge in water when alarmed. but in the Solomons, for e)(ample, they are more likely to take shelter in a tree. Studies in Guam have shown that at least during the warmer parts of the year activity occurs onLy in the mornings (Dryden 19(5). Here most breeding probably occurs early in the dry season (Wikramanayake & Dryden 191111). Ln captivity specimens from Guam have laid eggs in most months of the year (Groves pers.comm.) and Brandenberg (19113) e)(amined recently hatched animals collected in almost every month of the year from New Guinea. Mating and combat. performed quadrupedally, are desLTibed by McCoid & Hensley (I9l1 I). l)/i
Monitors of the World The clutch size of this species is probably smaller than would be expected of a medium sized monitor lizard, on account of the very small size of the females. A specimen from Guam laid 22 eggs over 3 years in clutches of between 1 and 4 (typically 2) eggs (Groves, pers. comm.). Luxmoore el al (198M) record a clutch of five eggs. McCoid (1993) reports that captive females from Guam lay up to four eggs in a one week period and a 38cm SVL road killed female contained ten shelled eggs. Kukol (1993) reports that a female of unknown origin and unreported size laid 30 (infertile) eggs between September and January in clutches of up to nine eggs. Wesiak (I 993a&b) reports that a captive female laid 25 eggs in five clutches over 26 months, with an average of 88 days between the last four clutches. Each clutch contained 4-6 eggs. Such observations indicate that when food is abundant mangrove monitors may attempt to reproduce continuously, producing large number of relatively small clutches. In this way a small bodied female can maximise her reproductive output Mankind appears to have introduced the mangrove monitor to a number of Pacific Islands in the last few decades. According to Uchida (1967) they have been present of Ifaluk in the western Caroline Islands only since the Second World War. Dryden (1965) repons that the Japanese may have introdllced the lizards to Japtan in the Marshall Islands before the war. The lizards flourished and soon began to raid the local chicken houses. When the Americans arrived the locals asked them for help in getting rid of the monitor lizards. They responded by introducing the dreaded marine toad (Bufo marinus) which proved toxic to the lizards. As the lizard popUlation dropped , however, the rat population began to rise. The Americans were asked for help once again, this time to get rid of the toads, but unfortunately there appears to be no record of their response (Owen in Dryden 1965). Gressit (1952) notes that marine toads were introduced to the Palau Islands for a similar reason, and suggests that the demise of the monitor lizards may have led to an increase in numbers of beetles known to be coconut pests. McCoid et al (1994) note that numbers have declined on Guam in the Marianas Islands. The mangrove monitor has a beautiful skin and as a result it is hunted in many places for its leather, which is used for drum heads and other purposes. It seems strange that international trade in this species is so small. Menens (1942) referred to it as one of the most heavily exploited monitor lizards. In 1980 trade in over 13,000 skins was declared but since then numbers seem to have been minimal (Luxmoore el al 1988). The species is said to be protected in Indonesia and so it seems likely that they are referred to as V.salvator in CITES documentation. In many places they are used as a food source but may also be persecuted because of their reputation for preying on domestic animals. In captivity the mangrove monitor can be a very timid and nervous animal. They need to be provided with a spacious enclosure that allows them to climb, and provided with plenty of hiding places. Mangrove monitors will bask at temperatures up to 50°C. A large pool of water is essential for these animals' wellbeing. Because males tend to be much larger than females court~hip and mating can be violent (Polleck 1979; McCoid & Hensley 1991). The first report of captive breeding comes from the Philadelphia Zoo, where a pair were housed in a 1.5m2 enclosure. Many clutches of eggs were prod uced and fmally two hatched after 198-199 days at 28-2<JOC (Groves, pers.comm.). Wesiak (1993a&b) housed three adulL~ together in a 3.4m 2 enclosure with a large pool of water and records an incubation period of 174 days at 26.5°C. Kok (1995) records eggs hatching after 152- 182 days at an unspecified temperature. Hatchlings weigh about 25g, measure 27cm 1L and will immediately accept baby mice and insects. Because females produce huge amounts of eggs particular attention 97
Little Book of Monitor Li zards needs 10 be given to Iheir Ilutritional needs. Suitable diet should include large insects, fish. !lirds. eggs and mammals. It seems likely that many of the animals .sold under the name \ .i"dintS are actuall y V. dorcolIIls.
O~ n
VARANUS }OBIENSIS Ahl 1932 Sepik monitor, Peach·throated monitor.
Oc::::J The Sepik monitor is usually known by the name of V kar/schmidli (Mertens 1951). Bohme (1991) recognised that Mertens had redescribed an animal /7 P originally named by Ahl (1932). This is another ;/ " .~ species about which very lillie is known . They can be di stinguished from V.indicus by the possession of smaller scales. partic ularl y on the neck and sides of the head, the bright red tongue with a black or light tip. the light colouration of the throat and the shape of the head. whi ch is slimmer than in V.indicus and reminiscent of V.sa/valor or even V.rudicollis (Mertens 1951 . Horn 1977). The light colour of the throat is much more noticeable when the lizards are annoyed and their throats are expanded . It reaches a length of at least 120cm TL (45cm SVL).
Merlens noted that Sepik monitors were sympatric with mangrove monitors around Marienberg on the Sepik River. where available habitats include swamps, rainforests and grasslands. but how the ecologies of these animals differ is unknown. In captivity these lizards have been observed to be vigourous diggers (Horn 1977), and it could be surmised Ihal Ihe Sepik monitor is less aquatic in habit than the mangrove monitor. However they also like to sleep in mUd. preferring it to water. Unfortunately observations of this species in the wild are entirely lacking. Whitaker et a/ (19R2) record the species from the Eastern and Western Highlands and East and West Sepik Provinces in New Guinea. Mertens (1959, 1971) and Swanson (in Horn 1977) also record specimens from Lae and Bulolo in Morobe Province (Horn (1977) gives "Eastern Highlands District" for Bulolo) and Brown River in ('entral Province. No exact locations in Irian Jaya have been recorded except for the location of the type specimen of V.jnbiensis; Yapan off the northern coast (Ahl 1932). The few data available strongly suggest that this monitor is widespread throughout the island except perhaps in the swamps and grasslands of the south. Horn (1977) notes that all specimens to date have been found in rainforests close to lakes at elevations of less than IOOOm. A field study of these animals and their counterparts would be highJy rewarding. In colouration the Sepik monitor shows a great deal of variation. "Peach-throated" monitors have throats that range from white through yellow to red but are always lighter than the body colour. Melanistic animals with reduced pattern are known, they may be found in coastal reg ions, but accurate location data is lacking in almost all V.jobiensis known . Some specimens are breathtakingly beautiful. Colour pictures of this lizard can be found in Hom ( 1977) and Sprackland (1992). In captivity this species tends to be shy and nervous, but usually groups of animals can be housed together safely. They will eat insects, small mammals. frogs and freshwater fish. Frogs are consumed avidly in captivity and may be an important food in the wild. Like other New Guinea monitor lizards they need to be maintained at a high temperature and with high hUlllidity. The Sepik monitor has a reputation for doing poorly in captivity. Newly imported 9R
Monitors of the World specimens are heavily loaded with a myriad of potentially lethal parasites, especially nasty amoebas. They need immediate and regular attention from a vet and should be dosed liberally with drugs until the prognosis is clear
VARANUS KINGORUM
Storr 1980
Kings' goanna. Kings' goanna is a very poorly known species that lives in the far north of Western Australia and Northern Territory. The very long tail (200-270% of the SVL) indicates that this is a rock dweUing goanna and they may be associated only with sandstone areas. It can be distinguished from all .tj other species by its very long tail, curious loreal crease on the snout and pattern. In colour it is basically brown with a black reticulum in juveniles that breaks down with age to form dark spots and flecks. Maximum size is probably no more than 40cm TL. The longest known male has a SVL of Ilcm, largest female is 9.2cm SVL (James et al 1992). Hatchling Kings' goannas are probably less than 6cm SVL. Very few specimens of this delightfullinle goanna are known to science. They appear to feed only on insects (orthopterans, termites, blattids and insect eggs). Specimens caught in February have been in reproductive condition . (Losos & Greene 1998; James et al 1992). Kings' goanna has been bred in captivity (Weigel, pers. cornm.) but no details are available the time of writing.
r.:: 1'0 f-~<"::~ ~M.
VARANUS KOMODOENSIS
Ouwens 1912 Kornodo dragon, ora.
The Komodo dragon is the World's most infamous lizard. Not only is it the largest and most aggressive living lizard, but it is also one of the most endangered. Komodo dragons live only in the driest, most remote parts of Indonesia, on the small islands of Komodo Rintja, Gillirnontang, Padar and the western tip of Flores. In keeping with the lizards' ancient aspect, their range is ridden with earthquake zones and volcanos. In 1970's the total population of Komodo dragons was thought to be less than 6,000 (Auffenberg 1981). There are suggestions that the poaching of deer has lead to the extinction of the Komodo dragon on Padar (Marcellini 1991). Although the Portuguese and Dutch had been "busy" in Indonesia since the 16th Century the Komodo dragon escaped the attention of modem science until 1910. Lieutenant Van Steyn van Hensbroek of the Dutch Infantry, who was based in Flores, mentioned to Ouwens that a particularly large monitor lizard was said to inhabit the neighbouring island of Komodo. When the Lieutenant visited the islands he heard reports that the animals grew to 6 or 7 metres long, but the largest he was able to catch was only 2.2 metres long . A collector was despatched to Komodo who returned to Java with two adults (290cm and 235cm) and two juveniles (I00cm) which were formally described in 1912. Ouwens tried to play down the stories of 6 metre long lizards, but doubtless felt obliged to report all that he had heard
99
Lillie Book of Monitor Lizards ahout the animals. Stories of the giant lizards spread very quickly and before long trophy hunters began to nock to the islands in the hope of shooting some of the ma~sive beasts. Dis<,;ounting the locals' account that the lizards rarely. if ever. exceeded three metres in length, the hunters haited the dragons with dead goats and must have found them very ea~y target~ as they grouped around the carrion. Despite stories of 4 or 5 metres animals being t:lken (e.g. Broughton I Y:lfl). the largest that reached Europe and North America were 2.75 metres long . The myths persisted however. until they were finally laid to rest by Walter Auffcnberg's \:l-month field study of the species which reported (1981) that the largest specimen ~vailahle was almost exactly 3 metres long. Several other species of monitor lizard attain a similar size, but none have the bulk of the Komodo dragon. The heaviest recorded by AlIffenberg was a 2.5m animal which weighed 54kg. When full of food the same animal weighed arnllnd IOOkg. Auffenberg believed that 3m lizards could therefore weigh up to 2.'iOkg , and although this figure is often cited as their maximum weight there is no hard t: vidence to support it. Komodn dragons inhabit areas of dry savannah and woodland. and frequent thick monsoon forest along water courses, They spend most of their time on the boundary of grassland and lorest where they have access to a wide range of temperatures within a small area, As .juvenil es they lead very secretive lives. sheltering under bark and feeding on insects (grasshoppers and beetles) and geckoes. As they grow they become too heavy to forage on trees and their diet shifts to one comprised mainly of rodents and birds (and the occasional porcupine) which are collected on or below the ground , Adult Komodo dragons are fearsome predators. They will attack and lcill weaker dragons and feed on a variety of snakes (including vipers and cobras), crocodile eggs and young and often raid the nests of megapode hirds (Lincoln 1974), But the bulk of their diet is made up of large mammals; goats, deer. pigs, horses and water buffalo. These prey are often caught by ambush or surprise, The dragon s hide in long grass along game trails and rush theit prey 8S it passes, crippling it by severing tendons in the legs before killing it with a bite to the throat or by ripping out the intestines. Auffenberg suggests that the lizards needed to get to within 1m of the prey without being detected for such ambushes to be effective. He provides pictures of a 320kg buffalo that was attacked and crippled by a 2.8m dragon and suggests that buffalo as large a~ 5YOkg are sometimes killed by adults. Sometimes adult dragons attack ridiculously large prey (see Chapter 4) but they usually select weak or young victims, They often feed on foals and young deer, even snatching baby animals from between the legs of the mother during birth. The dragons can identify heavily pregnant mammals by their smell and may attempt to induce miscarriage in those that are too large to be attacked successfully, The popular perception of Komodo dragons is of scavengers that congregate around dead animals. This is due largely to the fact that dragons can be easily attracted to carrion, where they provide an excellent show by carving the carcasses up and swallowing it in enormous chunks. A 42kg animal is recorded as having eaten an entire 30kg boar in 17 minutes, How important carrion is in the diet of animals undisturbed by man remains uncertain. During times of seismic and volcanic upheaval they may encounter many corpses but usually only animals killed by other Komodo dragons may be available as carrion. They are certainly adept at eating large animals and never leave more than 13% of a corpse (intestines, fur and horns are usually ignored). All of the large animals eaten by modem day Komodo dragons have been introduced by man . Diamond (1987) suggested that a few thousand years ago pygmy elephants probably formed an important part of their diet. Green et at (1991) report that the metabolic rates of young Komodo dragons do not differ notably from those of other monitor 100
Monitors of the World lizards. Body temperatures of individuals drop as low as 20°C at night and can reach above 40°C during the day. Many keepers (e.g. Lederer 1942) have commented on the intelligence of the dragons and in particular their ability to recognise individual people. Collins (1956) trained young specimens to jump through hoop and perform other dextrous acts to obtain food. The temperament of individual dragons varies enormously. Proctor (1929) published a picture of an infant playing with an unrestrained adult dragon at the London Zoo and stated "She would tear a pig to pieces but can be trusted with children" . In later years Ms. Proctor was confined to an invalid chair and was accompanied on her excursions through the zoological gardens by a dragon (presumably the same specimen) who "could not be restrained from snapping at the bedded out flowers" (Anon 1968). However some Komodo dragons have a naturally belligerent nature. Auffenberg records that one wild individual was well known for its aggressive behaviour towards people and would follow human footprints on the beach and invade tents. making off with articles of clothing. Not surprisingly the Komodo dragon is attributed with responsibility for many human deaths. Journalists like to blame the lizards for any unexplained deaths or disappearances, and more than one old soldier has been known to supplement his meagre income by displaying his war wounds to interested foreigners and describing them as the result of a dragon attack. Baron Rudolf Von Reding Biberegg is said to be the fust European victim of the dragons. He disappeared in July) 974, and only his hat, camera and a single bloodstained shoe were ever found (Blair & Blair 1988). The Komodo dragon is heavily protected and all commercial trade in the species is outlawed . Its skin is unsuitable for the leather trade and its only therapeutic use is as some kind of dubious "swimming medicine" (Auffenberg 1981). However they are still sought after by some animal collectors and their is little doubt that an illicit trade in the animals exists. Breeding at zoos in Surabaya and Jakarta, Java, has been reported many times (de Jong 1944, Busono 1974, Horn & Visser 1989, Soebakir, pers comm, Linus, pers comm) but elsewhere the lizards had never reproduced successfully until the U.S. National Zoo in Washington DC produced 55 baby dragons from 3 clutches of eggs (Walsh et al 1993, Jaffrey 1995). They maintain a pair of dragons in a 58m 2 enclosure with a soil substrate, at ambient temperatures of about 310C which drop to 170C at night. Basking areas of over 49"C are provided and the animals are fed several large rats each per week. Eggs are laid in a warmed nest area and hatch after about 237- 280 days incubation at 27.5-29°C in venniculite and water. The youngsters are housed apart, given UV light and reach a weight of about 300g after six months (Walsh et at 1993). Housed outside in Indonesia captive-bred dragons can reach lengths of 2m and weights of 20kg (females) or 30kg (males) after four years (Linus, pers comm). Unfortunately all youngsters produced in the US to date have the same mother. which makes them of limited use to future captive breeding projects. As a result the controversial decision was taken not to allow her to breed again and to sacrifice her final clutch of eggs to scientific study. Nevertheless the work of the zoo has greatly raised awareness of the plight of the Komodo dragon in the USA and, most importantly, promises funding for further field studies and direct conservation action within Indonesia. The success of the American breeding programme now hinges very much on the success of the decision to catch and ex port a further four adult dragons to the USA (Jaffrey 1995). Should these animals fail to breed it will reinforce the claims of sceptics who consider the programme to be politically and fmancialJy motivated and believe that a complete ban on the removal of adult dragons from 101
Little Book of Monitor Lizanis the wild is the best way to safeguard the future of one of the World's most remarkable animals. There is evidem.:e that, on Komodo at least, female dragons are oU01umbered at Icast :1: I by males (Darevsky & Kardarsan 1964, Auffenberg 1981) which makes the prohlems (1f finding a compatible pair particularly fonnidable. Further accounts of the care of Komodo dmgons in captivity can be found in Brongersma (1932), Tanzer & Van Heurn (I ,}:1X 1. Lederer (1942) , Oesman (1967), Galstaun (1973) & Lange (19119). Up to date information on the Komodo dragon breeding project can be found in the newsletter Dragon Doings. puhlished oy the National Zoo in Washington DC.
VARANUS MERTENSI (;Iauert 1951. Mertens' goanna, Rulliwallah.
Mertens' goanna is perhaps the most amphibious member of the monitor lizard family. It is found in northern Australia, from Western Australia east to western Queensland. According to Schmida (1985) they are t:ommon on waterways thraughout northern Australia. Gow (1981) records them from Groote Eylandt and Schurer & Horn (1978) and Storr (19110) provide location data on the mainland . Mertens' goanna has a long tail (up to 183% of SVL) which shows extreme lateral t:ompression . The nostrils are situated on the top of the head (Mertens 19511) and Cogger (1,}5'}) notes that they can be sealed whilst the lizard is submerged. In Western Australia Storr (I ,}XU) gives a maximum size of 47 .5cm SVL (113cm TL). Maximum size according to Horn (in Eidenmuller 1990) is 160cm TL. Bratzler (1965) records a 126cm TL specimen in captivity that weighed 49OOg. A pair of long tenn captives maintained by Eidenmuller measured HScm (female) and llOcm (male) TL after nine years. Gow (1981) records snout vent lengths of 30 and 40cm on Groote Eylandt. At Jabiru, Northern Territory, they reach sexual maturity at 28cm (for females) and 32cm SVL (for males). There is no apparent difference in size between the sexes. The largest male was 41cm SVL and the largest female measured 46cm SVL (Shine 19116). In this area they were most commonly seen around small t:reeks (lying either in very close to the water) rather than larger bodies of water and were often sympatric with estuarine crocodiles (Crocody/us porosus) . They feed largely on crabs, fish, frogs and turtle eggs together with small numbers of insects. Gravid females (containing up to II eggs) were collected in April and June and a female about to ovulate was collected in the wet season (December). This suggest that most breeding occurs in the dry season, but that some reproduction may occur at other times of the year. Egg size is given as 6 X 3.Scm, volume 77cc. In captivity clutch sizes of up to 14 eggs have been reported (Irwin 19116). Hatchlings measure 24-27cm TL and weigh about 24-28g (Bratzler 1965). Mertens' goanna is rarely found more than a metre or so from water. They are frequently found in rocky gorges and have been recorded along slow and fast moving rivers, reservoirs and billabongs (Bustard 1970: Schurer & Hom 1978). They are described by several authors as being crocodilian in habit, basking on the banks of lakes and rivers and sliding into the water at the first sign of danger. Swanson (1976) notes that when walking underwater they will keep their eyes wide open. During the wet season a great deal more habitat is available to them, and many move to temporary bodies of water at this time (Stammer 1970; Shine 19X6). Hermes (1911 I ) saw a IOOcm long Mertens' goanna collecting fish from a shallow pool by sweeping its tail in an arc to concentrate the fish close to its mouth and grabbing them
102
Monitors of the World from above. Like V.sa/valor, Mertens' monitor has to leave the water in order to swallow large food items. Another important adaptation for an amphibious lifestyle in V.merlens; appears to be its ability to maintain activity at low body temperatures. Schurer & Horn (197R) caught a specimen during the winter in water of only 17°C. The goanna had a body temperature of 18°C. EiderunuJler (1990) records specimens active in water of 26-32°C during the summer. Green & King (1993) record activity temperatures of 32.7°C for a wild specimen and 32.5 0 C for a captive one. These goannas are often found in large numbers along water courses. Schurer & Horn (1978) report seeing 12 specimens along a 50m stretch of riverbank. EidenmuJler (1990) saw five adults along 200m of the bank of Lake Argyll and Stammer (I (70) saw eight specimens along 200m of Lake Moondara. Despite their close proximity to each other they are not reported to routinely share basking sites. Not surprisingly, most of Mertens' goannas food is taken from the water. Crabs appear to be its favourite food , together with fish, frogs, crayfish, shrimps and amphipods. They also eat repti Ie eggs birds, mammals and a number of terresoial invertebrates such as orthopterans, spiders, dragonflies, beetles and bugs (Shine 1986; Stewart 1982; Losos & Greene I(811). They are known to scavenge among human rubbish (showing a particular taste for sausages) and probably eat carrion when the opportunity arises (Shine 19R6; Philippen 1994b). Stewart (I YR2) records that one ate almost a kilo of fresh buffalo meat in less than a minute. He also comments on the initial wariness of the goanna to humanity, how it eventually began to solicit him for bits of food and how, after two months, it eventually disappeared after having been tormented . Like other large goannas, V.merlens; adopts a bipedal stance when threatened and engages in bipedal ritual combat (Murphy & Lamoreaux 1978; Braithwaite (in Greer 1989); Green & King 1993). Murphy & Lamoreaux (1978) also describe other aggressive/defensive behaviours exhibited by these elegant creatures. Although little is known of their breeding habits in the wild, specimens kept outside in Queensland have laid eggs in March, buried in a vertical burrow 50cm deep (Irwin 1986). Another source (Swanson 1976) suggests that eggs are laid in leaf litter deposited at the end of a burrow, after which the entrance is tightly sealed. There are several reports concerning successful maintenance and breeding of this species in captivity (Brotzler 1965; Irwin 1986; Eiderunuller 1990, 1991). The size of the enclosure does not appear to be particularly important, so long as it contains a body of water large enough for the lizards to immerse themselves. Eiderunuller (1990) had great success with a pair kept in an aquarium of 150 X 60 X 4Ocm, comprised of about 70% water (heated to 2Roq and 30% land. He reports that the animals are very tolerant of each other and Irwin (I YH6) also conunents on the lack of aggression between specimens housed together. The enclosure should contain plenty of hiding places (hollow logs are ideal). These goannas will often rest on branches above the ground when given the opportunity. A diet of freshwater fishes, small rodents and insects is suitable. Schurer & Horn (1978) note that they have difficulty swallowing larger rodents and refuse small adult birds, although they wiU accept chicks. Worrel (1956) considered their favourite foods in captivity to be fish and frogs. Courtship in this species appears to be a very gentle affair. In captivity at least, it may occur at any time of the year. Eggs incubated at 29-32°C hatch after 182-277 days (Brotzler 1%5; Irwin 191\6). At 27 -2RoC they hatch after 265-316 days (Eidenmuller 1990). The hatchlings, which can be raised together, will enter the water immediately and take small fish and
103
Little Book of Monitor Lizards rode nt s. A Ithough this species is very rarely seen on dealers' lists it is hoped that the si[!llificant number of captive bred specimens produced in the last few years will result in this 1x-
Mertens 19511.
Mitchell's monitor is a small arboreal goanna found along th e waterways of no rthern Western Australia and Northern Territory. Its long compressed tail led Mertens ( 1l) )X) to place the species in the subgenus Varanus al o n[! with other large Australian goannas, but more recent studies suggest that this is a dwarf monitor of the Or/II/ria subgenus (e.g. Baverstock el al 1994). This livel y lillIe goanna reaches a maximum size of about 70cm TL. The tail is 173-210% of SVL (Storr IlJXIl). At hatching they measure less than 8cm SVL and sexual maturity is attained in both sexes at about 22cm SVL (Shine 1986). Mitchell's goanna is found in both freshwater and marine habitats. They are said to inhabit mangrove swamps and coasts as well as along inland rivers, streams, lakes and billabongs. Around Jabiru. Northern Territory, they occupy areas that are only intennittently flooded and arc usu ally seen on trees close to the water. During the wet season they expand their habitat to take advantage of temporarily fl ooded areas (Shine 1986). Diet in this area is comprised largely of fish and crabs. together with frogs, lizards, reptile eggs, small mammals, nestl ing hird s and terrestrial invertebrates (orthopterans, arachnids. beetles etc. ). A specimen examined by Losos & Greene (19R6) also contained a frog and Schmida (1985) considered fr ogs to be their most important prey item (he considers this diet to be responsible for the large numbers of parasites which the goannas harbour) . At Jaribu breeding occurs during the dry season. with gravid females found from April - June containing up to 12 small (2.5 X 1.3cm, volume 4.4cc) eggs. The diet of Mitchell's goanna indicates that they forage both on the ground and in the water. However, during most of the day (and throughout the night) they rest on tree branches overhanging the water (Peters 1971b. Shine 19R6). There appear to be no published reports of captive breeding for Mitchell's goanna. In captivity they are said to be very nervous and shy (Peters 1971 b; Murphy 1972) and need to be housed in a large. high enclosure with high temperatures and plenty of hiding places. both 011 and above the ground. In general they tolerate each other well but may harass smaller or weaker lizards. Th eir diet should contain animals of both aquatic and terrestrial origin .
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Monitors of the World
VARANUS NILOTlCUS Nile monitor, Water leguaan. Varanus nilolicus nilolicus Varanus nilolicus omalus
Linnaeus 1758 Daudin 1803
The Nile monitor is the largest lizard in Africa and also one of the most widespread. It is known from all parts of Africa except desert regions (Mertens 1942, Luxmoore et al 1988 ). More than a hundred years ago Nile monitors were reponed to live in Palestine (Tristram 1888). V.griseus is the only monitor found there now but the two species are so different that it would be very difficult to confuse them. Perhaps the Nile monitor once lived along the banks of the Jordan River, but today it seems almost cenain that they are restricted to the African continent. The subspecies V.niloricus ornatus is currently recognised on the basis of having a light coloured tongue and 3-5 rows of light markings over the back, compared to 6-9 rows in the nominate race (Mertens 1942, Loveridge 1953). V.n.ornalUS is supposedly restricted to the rainforests and coastal grasslands of western Africa. At present there is no evidence that these animals differ from the nominate race in anything but pattern, although observations on these animals in thick forests are sadly lacking. Nile monitors are found almost wherever there are permanent bodies of water. They are absent from deserts but present in most other habitats, from grasslands and desert fringes to rainforests , where they are found along rivers, swamps, pools, lakes and seashores. They will readily inhabit human settlements and cultivations where they are not persecuted. Barbour & Loveridge (l928) record them as high as 2000m above sea level. In 1<)29 lngleton published a photograph of a Nile monitor from South Africa which he claimed measured 213cm TL and weighed almost 19k9. He also claimed to have shot another 250cm long. No specimens of this size exist there today but Buffrenil (1992) considered that animals of this size could occur around Lake Chad. Charlton (l973), Patterson (1987) and Fitzsimmons (1934) suggest maximum lengths of about 15Ocm. Auerbach (l985) gives a figure of over 200cm. Specimens of 188cm (74cm SVL) have been recorded from Orange Free State in South Africa (de Waal 1978) and Boycott & Morgan (l988) refer to a female of 170cm, so it seems likely that in southern Africa occasional specimens may attain lengths of 200cm or more, but they must be rare. A male from Sudan with a SVL of 57.5cm weighed 5.9kg (Hirth & Latif 1979). A healthy male from the coast of Ghana (SVL 49cm) weighed 3,0 II g and what appeared to be a gravid female from the same location (SVL 44cm) weighed 1,478g (pers.obs.). Around Lake Chad males reach a maximum size of 207cm, females 155cm TL. Typically, males measure 150-17Ocm TL and weigh 5-10kg, females I 34cm TL, 3kg. In this area, where the animals are predated upon by man, they attain ages of around eight years (Buffrenil 1992, Buffrenil er aI1994) . McGraw (1992) stated that Nile monitors reach 200cm in length around Lake Malawi National Park, and that those from Mumbo and Boadzulu Islands were particularly large. Hatchlings weigh about 30g and measure around 30cm TL. Changes in skull and tooth morphology with age are well documented in this species (DumeriJ & Bibron 1856, Lonnberg 1903, Schmidt 1919, Peyer 1929. Rieppel & Labhardt 105
Little Book of Monitor Lizards
1979). Young spedmens have sharp pointed teeth that are gradually replaced with teeth that are broader and develop ridges on the crown. These changes are generally attributed to a shift in diet from fast moving prey such as insect and lizards to a diet of more sessile, but better armoured, prey such as molluscs and crustaceans that must be crushed in the jaws before being swallowed. Where crabs and snails abound they may form a large part of the diet, but in general Nile monitors eat anything they can fit into their mouths. [n the Shai Hills of Ghana they appear to be associated with large bat colonies (Bennett & Akonnor, ms). Elsewhere beetles, spiders, orthopterans, snakes, lizards, young crocodiles, fish, small mammals (including domestic ca ts), birds and their eggs, frogs, toads, crabs, snails, slugs, turtles, termites, caterpillars and reptile eggs (including those of crocodiles, agamids and varanids) are all included in the diet (Hesse 1889; Lonnberg 1903; Roosevelt 1910; Schmidt 1919; Barbour & Loveridge 1928; Cowles 1930; Pitman 1931; Loveridge 1933; Darby 1955; Cott 1960; Cisse 1972; Borquin & Channing 1980; Dial & Vaughan 19!P; Patterson 1987; Loso s & Greene 1988; Lang & Branch 1990; Van Rhyn 1991; McGraw 1992; Yeboah 1993). They also feed readily on carrion, including the remains of lion kills (Edroma & Ssali 19X3), often forage on human waste tips and will even consume human faeces (Bennett & Akonnor ms). Important prey items vary with habitat, but the great variety taken reflects that fact that Nile monitors forage on or below the ground, in trees or in water. Cisse (1972) suggested that they regularly revisit previous excavations to search for food, and may ambush nesting birds. They may use similar strategies to catch migrating shoals of fish (Pienaar \978). Cott (1960), Modha (1965) and others consider them to be amongst the most important predators of crocodile eggs and young. Ground nesting birds such as water Dikkop often nest in the same areas as crocodiles. It has been suggested that this strategy reduces the danger of other animals, particularly monitor lizards, preying on their eggs (Pitman 1957, Cott 196 I). Pitman (193 I) suggested that the monitors work in pairs to raid the nests, one diverting the female crocodile's attention and drawing her away from the nest whilst the other rushes in and digs up the eggs. Crocodiles will eat Nile monitors when they can catch them. Other known predators include mongooses and <.:obras (Branch & Branch 1992; Hinkel 19!i7). Nile monitors are most often seen basking on rocks and branches or in the water. Adults can easily outrun people over short distances, even over open ground and will almost invariably make for water when pursued . They retreat to burrows and abandoned termite mound s at night, but in warm weather they may remain outside, sleeping on branches or half submerged in water. Rose's (1962) report that they line their burrows with cow dWlg is unsubstantiated. Cisse (I <)72) found that in Senegal the animals left their burrows in the morning and did not return until late afternoon. This is confirmed by Edroma & Ssali (19!i3) who also note that whereas in warm weather rock or sand are the usual basking substrates, in cooler weather grass and branches are preferred. Of 35 burrows examined by them, none had been dug by the lizards themselves. During the dry season in tropical Africa and in the cooler months in temperate regions a<.:tivity is reduced or suspended (Cowles 1930, Cisse 1971). Juveniles are better at climbing than adults, but even large Nile monitors will climb readily. However they lack the dexterity to be classed as truly arboreal: Loveridge (I ':123) reports that specimens sleeping in trees have been known to loose their grip and plummet to their deaths. They are, of course, superb swimmers. In the wild Nile monitors can remain underwater for more than an hour (Ingleton 1929). Experiments with small specimens (1.4-4Jlkg) in captivity have shown that most dives last for 12-15 minutes, never more than half an hour. During these dives heart rate and blood
106
Monitors of the World pressure drop (Wood & Johansen 1<,)74). Hinh & Latif (1984) recorded an average body temperature of 2X.XoC, with a range from 20-37.2OC with activity above 26°C. An active specimen caught in the late afternoon had a cloacal temperature of 32°C whilst ambient temperature wus 25.3 0 C (pers. obs.). Population densities of 40-60 Nile monitors per km2 have been recorded in northern Kenya (Western 1lJ74). Our preliminary studies suggest that populations are equally high in parts of Ghana, where this species is completely protected. Very high densities are recorded for heavily exploited populations around Lake Chad (Buffrenil 1992). However despite its abundance, size and economic importance the Nile monitor is a very poorly studied animal. The most complete published· study of their ecology is from Natal, South Africa (Cowles I<')2X. 1930). Here they were found close to water between September and March and were relatively inactive during the rest of the year, sheltering in abandoned tennite mounds. Cowles was also the ftrst person to note the use of active tennite mounds as nest sites. The nests used are large mounds, usually situated close to water. The female tears open the nest ~nd deposits her eggs without attempting to cover them. The tennites quickJy repair the nest ~nd the eggs are incubated safely, with constant heat and hwnidity, providing the mound remains occupied by termites. Cowles (1930) suggested an incubation period of about 300 days, based on his observations of hatchlings emerging in November and December and estimated that eggs were laid during the hottest part of the year (December to February). However Branch & Erasmus (1982) record a female in Transvaal seen depositing her eggs in August (at the end of the winter) and considering known incubation times in captivity (see below) it seems likely that the duration of incubation is less than half, or even a third, of that suggested by Cowles. In more northern parts of Africa suitable termitaria appear to be unavailable and eggs are deposited in burrows. In Sudan eggs may be laid burrows dug into the clay walls of irrigation canals (Clouds ley-Thompson 1967). In Senegal eggs are laid from late October to late December during the wet season. Gravid females have been found in T~nganyika during November (Barbour & Loveridge 1928) and during early July in Zanzibar (Pakenham 1983). In Ghana we have found what appeared to be gravid females in August ~nd September. L~rge female Nile monitors can lay enormous clutches of eggs. According to Loveridge (1<,)34) up to 60 eggs are produced in a single clutch, Borquin (1991) found 63 eggs in a termite mound and there are many records of clutches containing over 35 eggs (e.g. Barbour & Loveridge 1<.)28, Pakenham 1983, Boycott & Morgan 1988). According to Buffrenil (1<,)<.)2) females mature at around 120cm 11., around Lake Chad and initially produce only ~bout ten eggs per year. Like other African monitor lizards, the Nile monitor enhances its chan<.:es of survival by producing large numbers of eggs that hatch comparatively quickJy. Most eggs weigh 46-52g and measure about 6x4cm. Therefore the weight of a clutch of eggs from ~ large female can approach 3,OOOg! It appears that females spend most of the spring ~nd summer feeding heavily and accumulating massive fat reserves which are then converted into egg yolk in the liver during the long period of inactivity during the winter. In less temperate parts of Africa the period of activity occurs during the dry season and may be shorter in duration (Buffrenil 19lJ2). This is reflected by the apparent smaller clutches of
•A detailed study of the e<.:ology of the Nile monitor, by Singrid Lenz, will be published later this year (1<,)95) as part of the Mertensiella series from the DGHT in Germany.
/07
Little Book of Monitor Lizards females from West Africa (e.g. Cisse 1976). The need for females to accumulate large fat deposits and then greatly reduce activity during ovagenesis appears to be important in a number of both temperate and tropical varanids. 11 is discussed further in the following chapters. Surprisingly there are few published accounts of interactive behaviours such as ritual combat or courtship in Nile monitors. This can be attributed to the secretive behaviour of these huge lizards. Adults have been seen wrestling on the ground (presumed to be courtship by Clements (19611) but interpreted as ritual combat by Horn (19115). They have also been observed standing on their hind legs (Wearne 1962). but bipedal combat has not been observed to occur in this species. The Nile monitor makes great use of its tail for defence and the battered condition of these appendages in old specimens is attributed to its regular use as a club with which to deter aggressors. A number of unusual behaviours have been noted amongst Nile monitors. A young monitor lizard that fell into a enclosure full of young (3Ocm) crocodiles seized several of the crocodiles and turned them onto their backs before being removed. The crocodiles were estimated to weigh twice as much as the lizard (Pooley 19611). According to Stevenson-Ham,ilton (1947) a monitor surrounded by four large lion cubs kept perfectly motionless apart from occasionally twitching its tail tip. The lion cubs watched closely, but appeared to interpret the movements as that of a snake and eventually wandered away. The same author reports that an eagle which seized a Nile monitor was in turn seized on the thigh by the lizard, which steadfastly refused to let go. When found by a ranger the bird was in a state of utter e)(haustion. There are few lizards less suited to life in captivity than the Nile monitor. Buffrenil (1992) considered that, when fighting for its life, a Nile monitor was a more dangerous adversary than a crocodile of a similar size. Their care presents particular problems on account of the lizards' enormous size and lively dispositions. Very few of the people who buy brightly coloured baby Nile monitors can be aware that, within a couple of years, their purchase will have turned into an enormous, ferocious camivore, quite capable of breaking the family eat's neck with a single snap and swallowing it whole. An enormous enclosure (at least 8m 2 and 2.5m high) is needed to keep these animals properly, fumished with a sizeable pool of water and plenty of tree trunks for the lizards to climb on. A period of inactivity during the cool winter or hot dry season (depending on the origins of the animals) is desirable. Nile monitors are prone to obesity and the diet should include significant quantities of non-mammalian food. A temperature range of 11l-30OC is suitable with basking spots up to 45°C. Very few records of captive breeding are available (Enright 19119). Animals should be housed apart except at breeding time. The small size of females suggests that finding a compatible pair could be particularly problematic. Best results would be obtained by obtaining a group of young, unrelated, animals and rearing them to adulthood. Eggs collected in the wild or laid by wild caught females hatch after 141-150 days at 27-30.5°C, 120-137 days at 30°C and 92 days at 320C (Boycott & Morgan 1988, Branch & Erasmus 1982, Olmstead 1987, Enright 19119). In captivity they are known to practise cannibalism (Charlton 1973). Animal dealers who sell Nile monitors under the pretence that they can be kept as pets are a despicable breed, but given spacious surroundings and suitable furnishings Nile monitors can be very rewarding animals to keep in captivity. Nile monitors are eaten in many areas and their organs and tissues used for medicinal purposes (Anon 1937). The skin is very durable and beautiful. Between 19110 and 19115 trade in live specimens averaged H16 specimens per year whilst trade in skins averaged over
IOH
Monitors of the World 40(),()()O per year. In 19lH! more than 700,000 sldns were exported (LU)(moore & Groombridge 1990; Buffrenil 1992). Most skins are exported from Mali, Nigeria, Cameroon and Sudan to Europe, particularly France. The uses of monitor lizards and the effects of exploitation for meat and skins around Lake Chad is documented by Buffrenil (1992, 1993, ('I III 1994). In Ghana the Nile monitor is known as mampan tintin, in Zambia as mbulu, nabulwe, hopani, nsamba or imbulu (Broadley 1971). An e)(tensive list of the common names of African monitor lizards can be found in Auerbach (1995).
~.U
VARANUS OLiVACEUS Hallowell IRS7 (;ray's monitor, bulaan
The extraordinary ability of monitor lizards to escape notice by ecologists and other field workers. despite their large size. is e)(emplified best by the case of Gray's monitor lizard. For 130 years. between 1845 and 1975, only a preserved juvenile and the skull of an adult were known. Despite several thorough investigations of the Philippine Islands in which they were believed to live no further specimens were (:) found. and the species was generaUy considered to have .d become e)(tim;t. Finally another specimen was discovered in the collection of the American Museum of Natural History (Auffenberg 1976). It had been collected on Luzon Island during the 1930s and triggered a series of visits to the Philippines which culminated not only in the rediscovery of the species but also in one of the most comprehensive studies of the ecology of a lizard species ever performed. Almost aU that is known about this e)(traordinary monitor lizard can be found in Auffenberg (1988).
pIf/ ?pZ6.
o~
Gray's monitor gets its common name from its previous scientific name of Varanus grayi. It is found only on southern Luzon and Catanduanes Island in the Philippines, where it inhabits the forested slopes of low mountains. Possibly its range was much larger in the past. but the development of agriculture has removed its habitat from most vaUeys. The hillsides freljuented by the lizard are covered with thick rainforest and have many cliffs and rock outcrops. Although its total range is small (about 5OOOkm 2) Gray's monitor appears to be common in many areas. However its very secretive habits and cryptic colouration enable it to evade detection. As in many other monitor species. male Grey's monitors grow larger than females. Maximum size reported by Auffenberg in 73cm SVL (176cm TL) and over 9kg . .On average adult males measure ti5cm SVL, 6.7kg whilst adult females measure 51cm SVL and weigh 2.6kg. Hatchlings weigh about 25g and measure about 35cm TL. Tail length in adults varies from IllI-162% of SVL. A very large and apparently old specimen was delivered to the San Diego Zoo during the 19!Ws. Its total length was estimated at 200cm. The lizard was unconscious when received and never recovered. On death it was sent to the Florida State Museum (Auffenberg. pers. comm.). The forests inhabited by Gray's monitor allow it to be active throughout the year. Temperatures are relatively constant and never high enough to prevent activity. Climatic data carl be found in Chapter 4 of Auffenberg (19gll). Body temperatures range from 27.8-3g.2°C 109
Little Book of Monitor Lizards and a critical temperature of 41.fi-42.4OC has been established. Males are more active than females and move throughout the day, whereas females' movemenl~ tend to be restricted to the mornings. Also males grow faster than females. Average growth rates are 3.5cm per month for juveniles and O.3cm per month for adult~. They reach sexual maturity by the third year of life, at 40cm SVL and I kg for females and 45cm SVL and 1.5kg for males. Gray's monitor spends much of its time in trees, but finds almost all of its food on or below the surface. It shelters in thickets of vegetation on branches. in rock crevices and in tree hollows. That this species likes to wedge il~elf into tight crevices is demonstrated by the large numbers of scratches seen on their backs and bellies. Unlike other well known monitor lizards. Gray's monitor relies largely on its cryptic colouration for defence and when threatened tends to remain immobile amongst tangles of vegetation. The most extraordinary feature of the ecology of this lizard is its diet. Juveniles feed largely on snails and crabs but between the ages of 12-1 R months the diet changes to include a large number of fruits. No other monitor lizard is known to feed on plant matter in the wild. but in Gray's monitor it forms a major part of the diet. Other important foods are snails. crabs, spiders, beetles, birds and their eggs. Fruits are only eaten when they are perfectly ripe and are collected from the forest floor. Both sugary and oily fruits are eaten, but the latter are consumed in larger numbers. Oily fruit~ are generally avoided by vertebrates because they contain chemicals that render proteins indigestible. so the ability to feed on them probably reduces competition between the monitor lizard and the other fruit eating birds and mammals with which it shares its range. Gray's monitor is sympatric with the water monitor V.salvator. and it has been suggested that it is only able to survive competition from this non specialised. gregarious animal by adapting to a largely frugivorous diet. Although a wide range of fruits are available in tropical forest~, Gray's monitor selects only a few of them. They appear to know the location of the trees that bear edible fruit within their home range. However although some trees bear large amount~ of fruit over several months the lizards are very picky and rarely spend long feeding below an particular tree but move about to collect a variety of fruit. Nor do they gorge themselves with food in the manner of many large monitor species. Food in the stomach accounts for only about 2% of their body weight, although many other species are known to consume individual prey items weighing 20% or more of their own weight. The need for a wide variety of different fruits is due to complex nutritional requirements and the need to avoid ingesting too much of any of the toxins present in the fruit. Least fruit is eaten between December and February. most sugary fruits are eaten between May and July and oily fruits most abundant from August to November and from February to March. The seasonal differences in amount of food available is reflected in the amount of body fat accumulated by the lizards. Fat levels are lowest from June to August and highest in October (the level varies somewhat between the sexes). Body fat may account for 5-12% of body weight depending on time of year. As a consequence of its unusual diet the alimentary tract of Gray's monitor is unlike that of any other species. They possess a caecum in which microbial degradation of plant matter may occur and the large intestine is much longer than in carnivorous monitor lizards, suggesting a need for more complete digestion of food items. The ability to feed on sedentary food items present in large numbers is also probably responsible for the very small ranges in which these lizards are active; from just over 2000m 2 to 27. 100m 2 However if the area of the trees used by the lizards is also accounted for. the mean activity range (14.ROOm 2) increases ten-fold.
110
Monitors of the World Lillie is known of the breeding habits of Grey's monitor. Reproductive activity occurs mainly between June and September, when day length is longest, temperatures lowest and rainfall highest. It is interesting that in Gray's monitor egg production seems not to depend on the use of accumulated fat , for fat bodies are smallest whilst ovaries are growing at their fastest rate. The first behavioural change associated with reproduction is bipedal combat between males which occurs as testes reach their greatest weight. Copulation has been observed in captivity and appear to be very gentle compared with that of other species. There is some evidence that long term pair bonding may occur in this species (see Chapter 5). In the wild a single clutch of up to II eggs is produced between July and October. The eggs weigh 40-50g and measure about 6.7X3.6cm. They account for up to 18.6% of female body weight. In captivity two clutches of eggs (total 14) may be laid within four months of each other and Auffenberg believed that this may occur in the wild as well. Nothing is known of their nesting habit~. but tree hoUows seem the most likely nest sites. Nor is there any good daw on the length of incubation. The smallest specimens are found from May to July, suggesting that the eggs may not hatch for over 300 days. The skin of Grey's monitor is rarely used for conunercial trade, but the meat is popular and the fat particularly so, because it is less liable to breaking down at high temperatures than that of the much more ea~ily obtained water monitor. Apart from pythons, mankind appears to be the only important predator of the adult lizards. On account of its very restricted distribution Gray's monitor has been placed on Appendix I of the CITES legislation and export of animals for commercial purposes is outlawed. In captivity this species poses a number of unusual problems. A large, high enclosure should be provided with plenty of hiding places both above and below the ground. An enclosure with 1)m2 of floor space is sufficient to house a pair, but animals are often intolerant of each other or may refused 10 feed unless housed singly. They enjoy being sprayed with water and should be provided with frequent showers. Unlike most monitor lizards Gray's monitor does very little digging and appears not to ingest much substrate with its food . The fruit eaten by Gray's monitor are almost all endemic to the Philippine Islands and none are suitable for use as human food . Thus the frugivorous portion of this lizard's diet may prove almost impossible to replicate in captivity. It has been established that captives will survive for long periods on a diet of animals alone (Behler, MitcheU, pers. comm.) but it is unlikely that successful breeding can be accomplished on such a diet. The only report of breeding comes from the Dallas Zoo (Card 1994a,b 1995c) where pulverised fruit, vegetable oil and frU\:lose are used to supplement a diet of rodents. These additives must be injected into the prey animals; the only fruits taken voluntarily in captivity are grapes. Females are capable of producing more than one clutch of eggs per year, but to date only a single, short-lived juvenile has hatched, after 21 '} days at 28°C.
see Varanus gouldii
VARANUS PANOPTES Storr 19110
III
Little Book of Monitor Lizards
VARANVS PlLBARENSIS Storr 19HO
Pilbara goanna. As its name suggests the Pilbara goanna is restricted to the Pilbara region of Western Australia. It reaches a maximum length of about SOcm TL. The largest seen by James et at (1992) were 17.2cm SVL (male) and 12.8cm SVL (female). The tail is 17S-205% of the SVL, suggesting that this is another rock dwelling species. Like Glauert's goanna. the Pilbara monitor has a boldly banded tail and rows of enlarged scales immediately behind the vent are present in both (Storr 1980; Storr et at 1983).
·ti sexe.~
We know nothing about the natural history of this glorious animal. Losos & Greene (1988) and James et at (1992) examined the stomach contents of just three animals and found only orthopterans, a spider and a skink. Johnstone (1988) records that they forage for orthopterans. Gravid females containing two or three eggs have been collected between July and October. There are no published reports regarding the care of this animal in captivity. They should probably be housed in the same manner as other long-tai led rock goannas.
~"
VARANVS PRASINVS Schlegel 1839. emerald monitor, green tree monitor.
0=
The taxonomy of this group has been subject to considerable revision (Sprackland 1991). The --,~c subspecies V.p .beccari and V.p .bo!?erti are considered separate species. V.p.lwrdensis i~ declared invalid, animals from Cape York in Australia are renamed as Varanus (erial' and those from Rossell Island off the far eastern coast of Papua New Guinea renamed as Varanus
n
tetenestes. V.prasinus was fITst described as Monitor viridis by Gray in 1831. According to Sprackland (1990) Gray's type specimen is lost. but according to Brandenberg (1983) it is probably RMNH 4X 12 in the Leiden Museum. the same specimen described by Schlegel eight years later. One of the prettiest and most endearing monitor lizards is this little gem from New Guinea An inhabitant of the rainforests. the emerald monitor is superbly adapted to an arboreal existence. Its cryptic colour varies from an intense turquoise green to black depending on its surroundings and its tail is used as a very precise and dextrous extra limb. The soles of the feet possess enlarge dark scales that may aid the lizards when climbing (Czechura 1980, Greene 1986). Like all the monitor lizards of New Guinea. details of their ecology remain a secret. They are found throughout the lowlands of New Guinea, except possibly for the swamps of the south, and on many islands. Location data can be found in Brandenberg (1983) and Spracklancl (1990).
112
Monitors of the World Emerald monitors, as their name suggests, are green, but usually have some black pattern. The degree of patterning varies, with some specimens unmarked and other covered in a thick. black reticulum. Animals which are entirely black and have keeled (almost spiny) scales on the neck are probably V.bogerti or V.beccarii. The emerald monitor inhabits rainforests, palm forests, mangroves and cocoa plantations (Cogger 1964; Room 1974; Czechura 1980) and have only been seen in trees or on vines. According to Sprackland (1990) they reach a total length of IOOcm. A specimen examined by Room (1974) from Pond etta in northern Papua measured 30cm SVL with a damaged tail. A captive specimen grew from 28cm TL to 30.8cm TL in six months (Sprackland 1989). Their food appears to consists mainly of large tree dwelling insects such as katydids, together with other orthopterans, huge armoured stick insects, roaches, beetles, centipedes, spiders and the occasional small mammal (Greene 1986). Before swallowing the formidable stick insects the lizards tear off some of their spinier legs. Although they eat mainly small prey they appear able to swallow mammals of a considerable size; a 135g lizard contained the remains of a 40g rodent (Greene 1986). The emerald monitor lays its eggs in arboreal termite nests (Allen (in Greene 1986), Allison, pers. conun). Hatchlings have been collected in October and may feed on termite or their eggs. The pra.l"illus-type monitors were considered to be dwarf monitors of the Odatria type by Mertens (1942). However in many aspects of their morphology they more closely resemble the illdicus-type lizards. Sprackland (1989) describes bipedal ritual combat which occurs in trees rather than on the ground. He also notes that emerald monitors appear to defend their tails rather use them for defence when threatened. The tail is clearly too fine a tuned organ to be used as a whip. Eidenmuller (pers. conun.) considers that females are comparatively rare amongst imported animals. Brandenberg (1983) found that 14 of 23 specimens examined by him were males. This beautiful monitor lizard is popular in captivity despite its- high price, which reflects the remoteness of New Guinea rather than the scarcity of the animals. They have a reputation for being very timid and should be provided ' with a terrarium dense with climbing supports and with plenty of hiding places on and above the ground . As with other forest monitors they should be kept warm and hwnid and given plenty of rain. In captivity they will sometimes take refuge in water when disturbed and wrap their tails around branches and sleep hanging on with just a claw or two (Brown 1983). In the wild emerald monitors feed mainly on insects and this should be reflected by their diet in captivity. When feeding on manunals they have a tendency to eviscerate their prey with their sharp claws before swallowing it. These monitors are tolerant of each other and can be kept in groups. Reliable reports of breeding are scarce (Barker 1984, Biebl 1993, Dedlmar 1994, Eidenmuller, pers.conun.). An enclosure of Im2 and at least IOOcm high is sufficient to house a pair of lizards. Suitable nesting boxes must be provided because both males and females show tendency to eat their eggs. Increasing the amount of simulated rainfall definitely triggers courtship behaviour in this species and in closely related taxa. Clutches of up to five eggs are produced, each weighing I U.5-11.5g and measuring about 2.0 X 4.5cm. Often up to three smaUer clutches are laid over a year. Eggs incubated at 27-29OC hatch after 186-190 days, at 30-32.8°C after 164 165 days. Neonates measure about 20cm TL and weigh 8.5-lOg. They attain maturity within two years. Sprackland (19H9) gives a growth rate of about 1.2cm per month for subadults and O.35cm per month for adults.
113
Little Book of Monitor Lizaros Male emeralo monitors teno to have larger heaos and broaoer tails than females. Hatchlings have an even brighter pattern than their parents. often with broad banos over the back which disintegrate with age. For unknown reasons the vivid green colour of these animals may fade after extended periods in captivity. The dubious subspel:ies Vp.k()rde/l.~is is said to have a mottled rather than banded pattern and may be a lighter green in colour. VARANUS PR1MORDIUS Mertens 1942
Blunt·nosed goanna Varanus primordius is a very poorly known goanna that was previously considered a subspecies of V.acallthurus (Mertens 1'J42d. 1'Jfi~. I%(). It is similar in appearance to V.storri but the spines on the tail are less well
developed and there are fewer midbody scale rows; up to ()() in primordius and at least 70 in storri (Storr I%(). It is known only from the far north of the Northern TelTitory and possibly the adjacent parts of Queensland and Western Australia (Gow I 'JR I; Cogger 1993; StOlT 19RO). It inhabits rocky areas where it shelters under rocks and in crevices. Other lizards account for the bulk of their diet, they are also known to eat orthopterans.lizards eggs and ants (Los os & Greene l'JIlR; James et all'J'(2).
'ti
VARANUS ROSENBERGI Mertens 1957
Rosenberg's goanna Rosenberg's goanna is among the best studied of the Australian monitor lizards. They are found throughout southern Australia; in Western Australia, South Australia, New South Wales and possibly the western edge of Victoria and are also present on a large number of islands including Thistle. Reevesby. Boston. Louth. Spilsby, Taylor's and Kangaroo Islands. It has been suggested that the goannas were purposely introduced to some of these islands (e.g. Reevsby Island) in order to reduce the numbers of dangerous snakes. On these islands Rosenberg's goanna is said to be very rare (believed extinct on Ainder's Island), whilst on Kangaroo Island they are abundant and seen more often than any other lizard. They inhabit a range of habitats, including woodlands, heathlands, scrublands and farmlands, but appears to be restricted to sandy soils (Ehmann 1976; Tyler et a11979; Robinson ct all9R5; Schwaner 19R5; Maryan & Robinson 19R7; Shea 1994).
'ti
Rosenberg's goanna is similar in appearance to V.gouldii and V flavirufus but is darker in colour (those from islands tend to be darkest), has a less distinct pattern and usually has a plain. dark tail tip. rather than a light or banded tip as is found in the other species. On some islands (including Kangaroo Island) the tail tip is banded rather than plain (Houston & Tyler 1979). In areas of Western Australia where they are sympatric with V.flavirufLis the two races do not interbreed. prompting StOlT (I 'JRO) to elevate them to a separate species. Hatchlings of Rosenberg's goannas are far more colourful than the juveniles of closely related species. They 114
Monitors of the World have an almost blue ground colour, with bright orange markings on the sides of the head, flanks and tail (see Green & King 1993). Rosenberg's goannas may reach a larger size than V flaviru!us, and tend to be more bulky. Maximum size in Western Australia is given as 103cm TL (Storr 1980). According to Tyler et at (1979) they can reach a length of 150cm on Kangaroo Island. The artimals are significantly larger on Kangaroo , Reevesby and Spilsby Islands than on the mainland. In all populations males grow about 12% longer than females (Storr 1980; Case & Schwaner 1993). Around Sydney they reach at least 50cm SVL (Shea 1994). Rosenberg's goanna eats a wide variety of animals. They will take larger mammals such as adult possums (either alive or as carrion) (Waite 1927 in Houston & Tyler 1979). Overton (19!\7) reports an attack on a young echinda. Usually they are said to feed on insects, spiders, scorpions frog s, snakes, lizards, small birds and small mammals (Houston & Tyler 1979). King & Green (1979) found that mammals (especiaUy rodents) and invertebrates (roaches, orthopterans, spiders, scorpions, beetles, centipedes and moUuscs) account for two-thirds of all food taken on Kangaroo Island. The remainder of the diet is made up of frogs, reptiles, lizard eggs and birds. A 770g specimen examined by Losos & Greene (1988) contained orthopterans, lepidopterans and the remains of a mammal. Rosenberg's goanna appears to do a lot of digging. They encounter much of their food below ground and dig enormous burrows. Tubb (1938) describes very long (over 9m), shallow (less than 30cm), forked burrows dug on the Banks Islands. Green & King (1979) found that burrows used in the surruner on Kangaroo island were much shallower than those used during the winter but shallower than those on the mainland. On Kangaroo Island the goannas may remain active throughout the winter, whilst the activity of those on the mainland is greatly reduced. Males are more active than females, and therefore encountered more often. Breeding occurs during early summer. Where tennite mounds are available they are used as nests. Eggs laid in February hatch 6-7 months later (King & Green 1979; King 1980). Ehmann el at (1991) provide an account of nesting behavioUl and incubation conditions. Several years ago there were proposals to eradicate Rosenberg's goanna from Reevsby Island to allow reintroduction of the almost extinct sticknest rat. It was claimed that the goannas had been introduced to several of the Banks Islands in the 1920s or 1950s to des troy the tiger snake population (Mirtschin 1982; Minschin & Jenkins 1985). This was refuted by Schwaner (1985) who suggested that the claims that the goannas were not native to the island were entirely speculative. Robinson et at (1985) argued that early visits to the islands had shown no evidence of goannas and that their removal was essential to allow the reintroduction of sticknest rats. Permission was given to destroy the goannas, but in the event the population proved so small that it was not worth eliminating and the scientists contented themselves with the extermination of feral cats (Schwaner pers.comm. Robinson pers. comm.). 1 can tind no published reports of captive breeding in thi s species. They should be housed in the same manner as for other large, burrowing goannas. An extremely infonnative and engaging account of Rosenberg's go anna is given by Green & King (1993).
liS
Lillie Book of Monitor Lizards VARANVS RVDICOLLIS (;ray IS45 Rough-necked monitor, flute monitor, monitor.
harlequin
?) }t
4.
The rough-necked monitor is one of the most fascinating ~ varanids. It is also among the most poorly studied of the " JC::".. ~ • Asian species. This ancient-looking creature, very aptly , • ~ ~~-~. described by Georg Horn as reminiscent of "a black knight ~
lations of this species in the wild are scarce; Ladiges (1939) encountered one in Sumatra resting on a log close to the water that ran up a tree to escape him. Jasmi (19S9) and Nutphand claim that the animals feed mainly on the ground and climb trees to escape from danger, often sheltering in tree hollows. The diet of this species is very poorly known. Schnider (in Werner 19(0) found only insects in a specimen from Sumatra. Mertens (1942) believed that a.1ts (and possibly termites) fonned a major part of the diet and were collected with the tongue. This is conftrmed by Auffenberg (l9XX and pel's. comnl.) who found termites, massive stick insects and tree centipedes in six specimens from Malaysia. One examined by Brandenberg (l9lB) had a stomach full of large cockroaches and grasshoppers and other from Surat Tharn in Thailand had a stomach full of crabs (Nabhitabhata, pers. COll1ln.). Five examined by Losos & Greene (Il.)gX) contained frogs and their eggs, sj.liclers, scorpions, crabs, cochoaches beetles and orthopterans. The rough-necked monitor may be active throughout the year, but is most in evidence during months of heavy rainfall (Nabhitabhata, pers. comm; Bennett & Lim in press) Rough-necked monitors rarely become lame and show a healthy dislike of humanity. In tum people often fear the lizard. According to Nutj.lhand the sj.lecies is often known as Ngu-Hao Chang (cobra elephant) in Thailand and are often attributed with Ihe abililY to spit venom. Ln 110
Monitors of the World Malaysia they are known as biawak serunai (flute monitor) and on Borneo as biawak punggur (rotting uee monitor). In captivity these monitors often have very nervous dispositions. Providing a very spacious enclosure and allowing the animals to hide above the ground will help them to overcome their shyness. Some authors (e.g. Sprackland 1992) have suggested that the animals are more secure when kept in groups, but care must be exercised because some individuals act in a very aggressive manner towards their conspecifics. Both Horn & Petters (1982) and NUlphand report that young specimens like to bury themselves in damp substrates and that they sometimes act dead when handled. In captivity they will accept a variety of invertebrates (freshwater crabs, earthworms and insects), small mammals, birds and freshwater fish. They need a constantly high temperature (no less than 23°C) and often respond to artificial rainfall by commencing courtship behaviour. Females usually prefer to lay their eggs above ground. Although eggs are often produced in captivity (up to three clutches per year each containing up to 14 eggs (Mehaffey in Bennett 1993b)) they rarely hatch. Eggs laid by a recently imported female were hatched successfuUy by Horn & Petters (I982) after 180-184 days im:ubation at 28-30°C. Hatchlings weigh about 21g and measure 25cm TL. Very young specimens have yellow bands over the body that disperse with age. Whilst adults from Thailand and Malaysia are often almost completely black, those from Borneo and Sumatra may be brighter in colour.
VARANUS SALVADORII Peters & Doria 1878. Salvadori's monitur, Crocodile monitor.
f?o ~
Oc::::::J
c;;P'(\ Salvadori's monitor is one of the world's most magnificent animals. Often cited as being "the .......,.. ~"c longest lizard in the world" virtually nothing is known of its ecology and the species remains one of the world's greatest zoological enigmas. This species was first described from a specimen 50cm SVL (I 65cm TL) caught by Dr Odoardo Beccaris, supposedly at Dorei in northwestern New Guinea. It was described by Wilhelm Peters (the owner of the Zoological Museum in Berlin) and Marchese Giacomo Doria (later the owner of the Natural History Museum in Genoa) and named after Conte Tommasso Salvadori, an eminent Italian ornithologist.
n
Salvadori's monitor does not appear to live anywhere other than the magical island of New Guinea. Al'l'ording to Whitaker el (II (1982) it is found in Western , Gulf, East and West Sepik provinl'es of Papua New Guinea. Mertens (I958) records it from the Ay River whilst Mertens (1971) and/or Brandenberg (1983) examined specimens from Aird Hill, Kikori, Kokoni River, Kwari (Dore), Hollandia Bivak, Lake Sentani and the Jamoer River. Al'l'ording to Mal'Kay (pers. comm .) they are found in mangrove and other estuarine swamps as well as drier forest from Port Moresby westward along the coastal regions as far as the Vogdkopf in Irian Jaya. Because they are restricted to the southern coast he considers rel'ord s from Lake Sentani and other parts of northern New Guinea to be incorrect. Salvadori's monitor is an excellent climber, able to support itself on vertical surfaces by hanging on with the hind feet alone. The tail is extremely long (up to 200% of the snout-vent 117
Little Book of Monitor Lizards length) and surprisingly prehensile; able to curl round branches to support the lizard when descending. It is also a formidable whip. Murphy & Mitchell (I <)74) describe how an adult male used the tail to make well-aimed strikes at its keeper's eyes. On the ground Salvadori's monitors tend to keep the tail tightly curled up in a spiral (Mertens 1960). In captivity males tend to be much bulkier than females, but there are no clear extemal differences. Indeed, several animals identified as males on the basis of hemipenal eversion have subsequently laid eggs (Madsen, pers. cOlT1ln.). According to the record books, Salvadori's monitor is indeed the longest lizard in the world. The record appears to be held by a specimen examined by Dr Michael Pope, a zoologist of Port Moresby, which measured 475cm from the tip of its nose to the tip of its tail (Wood I<)1l2). Unforrunately neither the lizard nor Dr Pope can be traced. However reliable sources suggest that some very large monitor lizards do occur there. According to Menzies (pers. comm.) the largest ever seen at the University of Port Moresby could have been 500cm long, but it escaped before it could be measured. Another specimen of 427cm has been reported from the area of Kikori, Gulf Province, Papua New Guinea (MacKay, pers. comm.) and a captive specimen circa. 300cm TL was reported to be kept at Moitaka (Allison, pers. comm.). Despite these claims the specimens available for inspection are all much smaller. The largest known example measured 244cl11 TL (Mertens 1962). Furthermore, long-term captives that appear to be in old age never attain a greater length. Even if much longer specimens do exist, Salvadori's monitor is a slightly built species compared with the Komodo dragon and there is no possibility that any will be found to compete with these giants in terms of bulk. About two-thirds of a Salvadori's monitor's length is made up of tail (Mertens (l96(J) cites tail length of 250-260% of SVL), and so even the largest of the supposed giants cannot have a body length of much more than 130cm. Females reach sexual maturity at less than 45cm SVL and the only known hatchling measured 11.5cm SVL, 45cm TL and weighed 55g (Hairston Adams, pers. C0I11111.). Geographical differences in tail length have been described in many species of monitor lizar'd (e.g. Storr 1980) and it is not inconceivable that specimens with head and body lengths similar to those of known specimens could sport very long tails, thus accounting for the apparently incredibly long specimens that have been reported from many reliable sources. There are undoubtedly still many undescribed monitor lizards in New Guinea and the possibility remains that the real giants belong to a species as yet unknown to science. Salvadori's monitor is often known as the tree crocodile, in reference to its arboreal habits, great size and large, bulbous snout. A description of the skull is given in Mertens (1950). The teeth of this species are particularly long and straight. As in the white-throated monitor the snout becomes particularly bulbous and prominent in old males. The toes are long and equipped with massive, curved , shiny-black claws. Observations in captivity tend to suggest that males spend less time above ground than females, but this is probably due to the fact that most specimens have lost at least a couple of toes by the time they are imported. The long tail lacks any sign of lateral compression and is reminiscent of the tails of dwarf monitors such as V.gilleni, but they are definitely found along rivers and are said to be good swimmers (McKay, pers. COffilll.). In defence the tail is often curled up in a manner very similar to that of the smaller New Guinea tree monitors (wasillll.\' group). Records of prey eaten by this extraordinary animal in the wild are sadly lacking. The only definite report appears to be that of Brandenberg (I L)X3) who found a bU'd's egg in the stomach of a preserved specimen. Mertens (I <)6(J) believed that their diet consisted of smaU
II X
Monitors of the World mammals. birds and their eggs. frogs and reptiles and Auffenberg (1981) claims that birds and their eggs form part of the diet. Suggestions that these lizards prey on children can be dismissed as utter nonsense, although they would probably consume them as carrion. According to MacKay (pers. comm.) the lizards feed largely on birds and often Lie on branches overhanging trails to ambush small mammals (such as rats and bandicoots) by dropping on them as they pass by. Salvadori's monitors are often very nervous in captivity. They need 10 be kept warm and with high humidity and provided with a huge enclosure that allows them ample opportunity to climb. Plenty of hiding places on and above the ground will help them feel secure. They seem to appreciate regular hosing downs with tepid water. They appear unfussy in their diet and will accept birds and small mammals, but larger specimens are prone to obesity Salvadori's monilOrs kill rats by shaking them very violently before swallowing them. The lizards are best kept apart except when breeding is attempted because there are several known cases of animals killing or maiming each other. Most of the damage is caused by the claws. The long teeth of these lizards can inflict horrific injuries on their keepers (Anon, pers. comm.) but long-term captives can become tame enough 10 feed by hand and have been described as "observant and curious" by several keepers who are not usually inclined to spout anthropomorphisms. Copulation has been observed in enclosures as small as 8m 2 (and at least 3m high) and often occurs during periods of short day length. Up 10 12 eggs (weighing 40-S0g and measuring about 8 X 3.Scm) may be produced in a single clutch (Philippen 1'}'}4). Females prefer 10 nest above the ground and up to three clutches (total of 17 eggs) have been laid over a year. Only one successful breeding is known, with a single youngster hat.ching after 176 days at 28-290 C (Hairston Adams, pers. comm.). In captivity they can Live in excess of 20 years (Mitchell, pers. comm.).
VARANUS SALVATOR Water munitor, Asiatic water monitor.
Varanus salvalor salvalor Laurenti 1788 Varanus salvalor cummingi Martin 1838 Varanus salvalor nuchalis Gunther 1872 Varanus salvalor marmoraius Weigmenn 1834 Varanus salvator biviltalus Kuhl 1820 Varanus salvalor logianus Peters 1872 Varanus salvator andamanensis Deraniyagala 1944 The water monitor is one of the largest and most widespread of the monitor Lizards. It is of greater economic importance than any other varanid and millions are ki lied each year for their meat and skins. Despite this heavy collecting water monitors are still very common in many areas. although in India numbers have dwindled severely in the last 150 years. Large populations can still be found on the Andamen and Nicobar Islands, and in Sri Lanka. but on the mainland they have survived only in Orissa, west Bengal, Assam, around Calcutta and in the Garo Hills. They may also be present in the eastern Himalayas (Parry 1932; Smith 1935; Whiraker & Whitaker I,}80; Whitaker & Khan 1982; Auffenberg 1986; Luxmoore & Groombridge I,},}(); Das 1n'}; Pandav 1993). Its disappearance appears to be due to a combination of oven.:ollecting and habitm destruction, especially the clearing of mangrove forests. Similarly, populations in Bangladesh appear to have been decimated in recent years 119
Little Book of Monitor Lizards (Khan 1088). Further south the animals are stili plentiful in most areas, with large populations reported in southern China (Yunnan, Kwantung, Kwangshi and Hanain), Burma, Thailand, Laos, Kampuchea, Vietnam, Malaysia, Borneo, the Philippines and the Indonesia n Islands as far east as Flores and Sulawesi or Halmahera (Peters & Doria 1878; de Rooij 1915; Schmidt 1927 , Smith 1930; Merten s 1942; Nutphand; Harrison & Lim 1957; Auffenberg 19R I; Luxmoore & Groombridge 1990; Gaulke 1992; Darevskii pers. comm). Small populations Illay sti ll exist on island s around Hong Kong (Romer 1963). Their numbers in Kalimantan are said to have declined seriously in recent years, although large populations sti ll exist in many parts of Borneo (Unlam & Untam 1988; Luxmoore & Groombridge 1990). In most parts of the Philippines numbers have greatly declined within living memory (Gaulke I 092b, 1986). In many areas water monitors are extremely numerous; ErdeJen (1988, IlI91) recorded almost 120kg of water monitor along a 1km stretch of riverbank in Sumatra, one of the highest lizard biomasses recorded anywhere in the world. Munsch (1987) saw seven specimens piled on top of each other on a riverbank. [n Bangladesh Khan (1988) estimated densitie s to be around 7 per km2 in suitable habitats. Water monitor can be found close to the centre of some of south-east Asia's largest cities, but they reach their highest densities in mangrove forests and are never found far from water, be it a ditch or an ocean. Their ability 10 u'averse large bodies of water has allowed them to co lonise many remote islands, including those of the Krakatoa group, where they had established themselves within 25 years of Ihe infamous eruptions of 1883, long before any other large vertebrate (Rawlinson et at 1990). Its abililY to survive where other animals cannot must be due largely to its very broad diet. Young animals feed largely on insects. Crabs, molluscs and fish form the bulk of Ihe adults' diet in many areas, but they will swallow anything even remotely edible. Snakes, turtles, tortoise, crocodile eggs and young, birds and their eggs, frogs, lizards, rodents, monkeys, small deer, carrion and waste from people, including hwnan corpses and human faeces are aU included in the diet (Taylor 1922; Vogel 1979; Deraniyagala 1931, 1953; Grandison 1972; Losos & Greene 1986; Auffenberg 1980, 1986; Rawlinson et at 1990; Gaulke 198%, 1991 a; Traeholt I 993a&b, 1994). W ater monitors will gorge themselves when given the opportunity, and become so bloated they are unable to offer muc h resistance to predators (Smith IlI31). They are able to eat the notorious marine toad (Bulo marillus) without ill effect (Gaulke IlI91 a). Traeholt (1994a) found that water monitors in some areas of Malaysia appeared unable to catch fish but elsewhere fish may fom1 a regular part of the diet (Bennett, in press h). The water monilor is said to reach a tOlal length in excess of 3 metres. Th e largest specimens come from Malaysia, particularly around the Cameron High.lands (Lim 1958; K.han 1969; Anon IlIX3), where specimens over 250cm TL are sometimes encountered. Jasmi (1088) record s that wild specimens ca n weigh up to 25kg. Thailand is also home to some huge water monitors (Nutphand, Taylor 1963) but elsewhere the water monitor attain s smaller sizes; largest found in Java are around 210cm TL, 200cm in Sri Lanka, l70cm in Sumarra and mainland lndia and less than 150cm on the island of Flores (Vogel 1979; Deraniyagala IlI53; Werner IlIOO; Das 1989; Auffenberg 1980). In most areas males reach a larger size than females and probably grow faster and are more active. In most populations sexual maturity is attained around 120cm (females) and 130cm (males), but specimens from India can breed at about 10Ucm TL (50cm SVL), which they can attain after two years under good conditions. In tropical areas with abundant food resources water monitors may breed throughout the year. Elsewhere mating and egglaying OC(ur at the beginning of the wet season. There is surprisingly little data available about the reproductive biology of this lizard in the wild
120
Monitors of the World (Biswas and Kar 19~ I; Erdelen 1988; Gaulke 19~9b, 1992). Clutches from large females typically consist of about 15 eggs, but up to 40 may be laid over a year. Nest sites include burrows (espe<:ially in elevated, sandy positions), abandoned and active termite mounds and possibly tree hollows (Taylor 1963). Incubation times appear to vary widely, but fully developed eggs may remain dormant for some time and do not hatch until rainfall is plentiful (Nabhitabhata, pers. comm). It has been suggested that females return to nests in active termitaria and release the young after they have hatched (Boonratana 1988). Young water monitors are more brightly coloured than their parents, but show no unusual patterns. They spend most of their time in trees. Water monitors are active at lower body temperature than most other varanids, and seek out microhabitats that allow them to maintain relatively constant temperatures (Wikramanayake & Green 1989 - see discussion under Vbengalensis). Traeholt (1995) records temperatures of 29.5-37°C with average activity temperatures of 30-31 °C and mean basking time of 38 minutes per day. Their metabolic rates are also lower than those of many other monitors (Gleeson 1981). Most of the day is spent lying in or close to water and in many areas the lizards are most active in the mornings. At night they shelter in tree, burrows or thick vegetation. The burrows of water monitors can be enormous; more than 10 metres long with tunnels large enough for a man to hide in (Traeholt in pressa). During wet seasons the lizards cover much larger areas as the amount of suitable habitat increases (Auffenberg 1980; Erde len 1988). Traeholt (in press b) records that populations of water monitors in different habitats display very different activity patterns. Bipedal combat is described by Honneger & Heusser (1969), Vogel (1979), Gaulke (1989b), Rese (1986), Horn (1994) and social hierarchy by Daltry (1991). Water monitors are among the most easily available varanids in the pet trade, but their enormous size makes them one of the most difficult species to care for properly. Breeding in captivity has been reported many times, but there are few examples of females reproducing consistently (e.g. Honn eger 1'171; Anon 1981; Bowers 1981; Groves 1984; Hairston & Bun;hfield 1992; Andrews & Gaulke 1990; Ettling 1992, Jes 1994; Vogel 1994; Andrews 1'1'15). Water monitors are unable to tolerate each other in cramped spaces (Daltry 1991). Courtship and mating are often very violent and finding a compatible pair can be problematic because animals collected from different areas may not respond to each other, but also because females are often much smaller than males and are less conunonly collected. Unfortunately there is no way of distinguishing the sexes with certainty without resorting to internal examination. Outside the breeding season the animals must be housed apart in aU but the largest enclosures. A minimum of 6m 2 is required by each adult . Large pools of water do not seem to be essential, but the animals should be allowed to immerse themselves if possible. Females are particularly aggressive just prior to egglaying. Length of incubation in captivity varies, sometimes even amongst eggs from the same clutch (Kratzer 1973). At 300 C they hatch after 1~0-327 days. Water monitors grow very quickly and can allain adult size within 30 months given good feeding . A varied diet should be provided and care taken that the animals do not become too fat. Suitable foods in captivity include crabs, fish, molluscs and large insects as well as birds and rodents. Many subspecies of the water monitor have been described and no records of interbreeding between subspecies exist. The Javan water monitor (Vs.bivillarus) is a brighLly coloured water monitor, whilst Vs. collianus is a darker form from Sulwesi and adjacent islands (Mertens 195'1) and VS.alldamallellsis is a melanistic race from the Andaman Islands 121
Little Book of Monitor Lizards (Oeraniyagala 1944. 19(1) The name VS.komailli is used to describe many black water monitors that appear in the wildlife trade, but no such subspecies has been formally described and black animals attributed to many subspecies are known from many coastal regions (Bennett 1995b). The differences between the subspecies on the Philippine Islands are the best documented (Gaulke 19R(" 1989b, 1991b, 1992a&b). The Philippine water monitor (V.I.marmoratus) inhabits south Luzon, Samar, Ticao, Palawan, Calamian, Sogon, Mindoro and the islands of the Sulu Archipelago as far as eastern Borneo. It reaches a size of about XOCIl1 SVL (200cm TL). The rough-necked water monitor VS.lluchalis attains a maximum size of about 60cm SVL and is distinguished by its large neck scales. It lives on Cebu, Ticao, Negros. Panay and Masbate and may have been confused with the rough-necked monitor on some occasions. Specimens from Masbate are particularly dark. The beautiful Cuming's water monitor (Vs.(umill/:i) is found on Mindanao, Samar, Layte, Bohol and Basilan and reaches a maximum size of about 70cm SVL (150cm TL). It does not appear to be closely related to the other races and may have different origins. Animals of a similar appearance have been collected from the eastern coast of Borneo. Water monitors from the remainder of the range are usually known as Vsalvalor salvator, but a biochemical study of the relationship between races of this remarkable animal would probably reveal some surprises. For captive breeding attempts it is highly desirable that both members of the pair have the same geographical origins. Populations at the eastern end of the range appear to be suffer pa.rticular heavy infestations of skin parasites, which make holes in the hides and greatly reduce their commercial value (Luxmoore & Groombridge 1990). On Bali the water monitor is known as alu, on Flores as weli. Elsewhere in Indonesia and in Malaysia they are known as biawak air. In Thailand they are known as hiah, but thi s word is considered offensive by many people and the term Tua-nguen-tua-tong (a creature of silver and gold) is best used with strangers. In Sri Lanka they are called karabagoya, in the Philippines Halo, in Bengali ram godhika and in Bangladesh (where they are rare) as pani gudhi or pani goisap.
122
Monitors of the World
VARANUS SCALARIS Mertens 1941
Banded tree goanna This goanna was originally described as a subspecies of V.timorensis (i.e. V.timorensis sea/aris). A year after Mertens recognised it as a separate species (l957a) he considered that the differences between similis and sea/aris were too slight to warrant use of sea/aris as a specific name (Mertens 1958). V.sea/aris has bands over the back which are lacking in V.similis and the latter has slightly fewer rows of scales around the body (107-117 vs. 110-129). Furthermore, male V.sealaris have spines just behind the vent which are absent in both v.timorellsis and V.similis (Schmid a 1971 , Storr 1980). Storr (1980) treated V.sea/aris as a subspecies of V.timorensis but Storr et al (1983) refer to it as a separate species. Their colour picture of this animal shows no sign of bands over the back. The differences between sealaris and similis are not at all clear to me.
'ti
This goanna is widespread throughout the tropical Northwest of Australia. They can be distinguished from v.timorensis by examination of the tail, which is round in cross section rather than compressed. They reach a maximum size of about 60cm TL. Colour and pattern vary enormously, suggesting that V.sealaris may turn out to be a complex of several species (Mertens 1958; Storr 1980). A race from central Queensland with rusty red stripes over the back (known as "v.pel/ewensis") is likely to be described as a new species. Specimens from the rainforests of northern Queensland have bright yellow or orange throats (Schmida 1971; Swanson 1976; Green & King 1993). These lizards occur almost wherever there are trees and are said to be absent from some sandstone areas, treeless grasslands and semi-desert Smith (1927) commented on the climbing ability of this goanna and noted that they would not attempt to bite when captured. According to Shine (1986) V.s calaris is active only during the wet season. Schmida (1971) found 14 specimens in 50m 2, all sheltering in hollow branches, and saw them hunting for large insects in trees. Little is known of their diet. Four specimens examined by Losos & Greene (1988) contained a skink, a scorpion and some insects. Schmida (1971) reported that they could also eat small agamids, lizards and birds. He reports that a specimen 20cm TL attacked and swallowed the tail of a gecko almost the same size as itself. Cogger (1973) suggested that they ignored frogs which shared their tree hollows. In captivity both youngsters and adults will hang from branches by their tails (Ruegg 1974). Some races of V.scalaris can be sexed by looking for spines on either side of the males' vents (Mertens 1958), but according to Schmida (1971) this is not reliable for V.similis. Unlike the Timor monitor, the spotted tree goanna is an aggressive lizard and animals housed together will often fight fiercely. Cannibalism is not unknown . Males are particularly rough with females during courtship and can fatally injure their intended mates. Nevertheless captive breeding is quite possible if adequate space (at least 1m2 of floor area) and plenty of hid.ing places can be provided (Ruegg 1974; Broer & Horn 1985; Eidenmuller & Wicker 1991). Up to eight eggs are laid which hatch after 115-139 days at 26-30 oC into 3.4-5g youngsters. The hatchlings have similar pattern and colouration to the parents. They do well on insects and tiny portions of rodents and will also accept small freshwater fish such as guppies. It may be
123
Little Book of Monitor Lizmds necessary 10 raise hatchlings separately. Spoued tree goannas can live for more than 15 years in captivity (Bennett I ,:!':!4b).
VARANUS SEMJREMEX
Peters 1869
Rusty guanna The rusty goanna is a very poorly known monitor lizard from the nonhern coast of Australia. It appears 10 be restricted to the eastern coast of Queensland where it is found in mangrove swamps. on coasts and along freshwater streams and swamps (Cogger 1981). Mertens (1958) records them \j from Woodstock and Coquet Island off Queensland. Dun son (I ':174) examined specimens from Townsville and Bowen in Queensland. Glauert (1951) includes the species in a key to the goannas of Western Ausrralia and Mertens (1961) describes a specimen supposedly from the Ord River in the extreme north-east of Western Australia. This animal was similar 10 those from Queensland but had a longer tail (178 % of S YL compared with 134-160% in Queensland). However since I ':161 no further specimens from outside Queensland have come 10 light. so it must be presumed that the species is restricted to that state. Even in Queensland the species appears 10 be rare. Covaceviich (pers. c:omlll.) reports that she has seen only six specimens in twenty years at the Queensland Museum. Wilson & Knowles (I ':!8l\) report that those from northern parts of Cape York Peninsula are darker in colour and have a stronger pattern than those from further south. The rusty goanna is sometimes known as Y.boulengeri (Kinghorn I ':I24a). This enigmatic little goanna reaches a maximum size of about 60cm TL. James et 111 (I ':12) give a maximum size of 27cm SYL and consider sexual maturity 10 be attained around 15cm SYL. Mertens (1961) reports a length of 23.5cm SYL (over 66cm TL) for his specimen from Westem Australia. Swanson (1976) gives a maximum size of 75cm TL. Six specimens examined by Dunson (I ':174) weighed 150 - 294g. Bustard (1970) records collecting rusty goannas from seasonally tlooded mangroves around Townsville. as does Dunson (I ':174). Hedley (in }(jnghorn 1':I24a) found one running along a beach. Its favourite food appears to be crabs (Dunson I ':174; Swanson 1976; Losos & Greene 1988; James et 111 I':1':12). Other prey include frogs. fish and insects. All prey fo und by James et al (1992) were aquatic in origi n but Dunson (I ':174) suggested that small mammals are also included in the diet. The rusty goanna appears 10 be an arboreal species which lives in hollows and on branches of trees overhanging the water. According to Dunson. in the mangroves around Town svi lle they forage over exposed mudtlats at low tide. This species is equipped with a salt gland that senetes sodium. chlorides and potassium, enabling lizards from saltwater environments 10 obtain all their freshwater by eating brackish-wate r prey. Examination of museum specimens led James et al (I ':1':)2) to conclude that breeding occurs in the late wet season (between February and April). The only gravid specimen examined by them contained two eggs, but cllllches can contain as many as 14 eggs (Horn in James et 111 19':)2). Ritual combat of the rusty monitor is des~ribed by Horn (1985). Opponents lie vent (0 veil! grasping eal:h other with all four legs and attempt to flick each other over in the typical Odatrian manner Little is known about the captive I:are of this species in captivity. the only published accounts being those of Peters (I ':J6l\, 19me) and Pollock (I ':Il\2). They should be kept warm and provided with a large te n'ar iulll with plenty of branches to climb on and a pool of water at
124
Monilors of the World least large enough for th e li zards to immerse themselves. They are said to be very peaceful and tame in captivity and will eat small mammal s, birds and eggs as we ll as their usual a4 uatic prey.
VARANUS SlMlLIS Spotted tree goanna
~
Mertens 1958
Differences between thi s goanna and Vsca/aris have been outlined above. Bohme (1988) considered V similis to be "proba bly a valid spec ies" on the basis of its hemipenal morphology. This monitor was previously known as Varanus rinwrensis simi/is. It is fo und in northern Australia and the south of New Guinea (the Wes tern Provi nce of Pap ua and the adjacent part of Irian Jaya (Whitaker el aL 1982; Brandenberg 1983)). Because nothing is known of the lifestyle of the ani mal s in New Guinea and very few publications distinguish the Australian races from V. sca/aris, this animal is discussed under Vsca/aris. Captive care and breeding is reported by Peters (1968), Schmida (1971) , Ruegg (1974), Chippind ale (1991) and Lambertz (1993. 1994).
VARANUS SPENCERl Lucas & Frost 1903 Spencer's goanna, plain goanna Spencer's goan na is the least known of the large Au scralian monitor lizards. It appears to live only in grass lands on the clay plains of eastern Northern Territory and north-western Queensland (Cogger 1993). They usuall y reach lengths of 100cm TL (Schmida 1985) with a max.imum of about 125cm TL. The tail is only slightly longer than the head and body (103-107% of SVL). lllis is a heav ily built spec ies th at often has a very thick tail base and attain s weights of ov er 2.25kg (Mertens 195 8; Bustard 1970). Hatchlin gs measure about 22cm TL, 13cm SVL (Peters 1986) . The short toeS are equipped with lon g powerful claws which enable these lizards to burrow throu g h clay. They are said to be most active between August and October (Schmida 1985 ). Pengilley (1981) found large numbers of femal es looking for nest sites among piles of red soil dumped at the side of a road in late September and early October. A wild caught fem ale laid eggs at the beginning of November. Clutch size is large, with up to 31 eggs. each measuring about 5 X 3.5cm, recorded from large females (PengiUey 1981).
\j
Spencer's · goannas usually shelter in burrows or large cracks in the clay and often inhabit areas devoid of trees (Stammer 1970; Swanson 1976). In captivity they are able to climb qu ite well (McKeown pers comm.) and so may ex plore crees where they are present. The adu lt female s examined by PengiUey (1981) had eaten mammals, large snakes. agamids. mammals and in sects (mainly orthopteran s) . A specimen examined by Stammer (1970) contained lar ge numbers of beetles. The stout bodies suggest that they are inactive thro ughout the winter, but there are no direct observat ion s to substantiate thi s. Bi pedal ritual combat in th is species was ftrst reco rded by Waite ( 1929), who mistook them for perenties . (Horn 198 1). A burrow, pro bably intended as a nest is depicted by PengiUey ( 198 1).
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Little Book of Monitor Lizards
There are few references to the care of this species in captivity (e.g. Peters 1969a,c, 1970a, 1<)7 I, 19X6). They require a spacious terrarium which provides plenty of opportunities to dig and would probably benefit from a seasonal reduction in activity. Eggs laid by a wild caught female hatched after 133-140 days at 29°C (Peters 1986). juveniles are much more colourful than the adults, with bright yellow bands over a glossy brown back. They double in size within six weeks. [n captivity, Spencer's goannas are said to be somewhat nervous but tolerant They can live for at least 15 years (Snider & Bowler 1992).
VARANUS STORRI
Storr's goanna Vllranus storri storri Mertens 1966 Varallus storri ocreatus Storr 1980. Storr's goanna is another spiny-tailed dwarf species found in inland areas of northern Australia. VSfOrri ocrealUs '\;1 occurs in Western Australia and Northern Territory, \islOrri s/(Irri is known only from Queensland. The species can be distinguished from Vaculllhllrus by its smaUer size, fewer rows of scales around the belly and their duller panern. They are distinguished from Vprimordius by possessing spiny rather than mucronate scales on the top and sides of the tail. VSlOrri ocrea[Us is distinguishable by the presence of enlarged scales on the last joint of the hindlegs. Like other races from the far north they tend to have rdatively longer tails (up to 190% of SVL compared with less than 150% in VSlorri slorri) and limbs (Mertens 1966; Storr 1980). The maximum size of Storr's goanna may exceed 4Ucm TL (Peters 1973) but usually they reach a length of around 30cm. Maximum size found by James el al (1992) was 13.9cm SVL for males and 12.6cm SVL for females. In general however, males are no larger than females and the latter may become sexually mature at a larger size (9.3cm SVL) than males (H.9cm SVL). How the habitat and behaviour of this species differ from Vprimordius is not yet clear. Peters (1973) found them in rocky areas with dead trees, Swanson (1976) cites dry rocky areas as their home and according to StanUller (1970) they are found in burrows under rock or spinifex. Stirnberg & Horn (19H I) found them in open woodland in Queensland, sheltering under piles of rocks. Storr's goanna appears to be less arboreal in habit than VacilIuhurus. According to Bustard (1970 in Greer 19H9) Storr's goannas live in colonies. This is supported by Peters (1973) who found 22 specimens in O.75km 2 of grassland and suggested that the total population was closer to 50 animals. They were found in individual "U"-shaped burrows under large rocks. In September the animals were most active in the morning and late afternoon, spending the hottest part of the day below ground. This lively little goanna appears to be mainly insectivorous, feeding largely on orthopterans and also taking skinks , beetles, aIllS and spiders (Losos & Greene 19HH; James 1'1 al 1992). Peters (1973) believed they preyed heavily on geckoes. Reproduction Illay occur throughout the year in this species (James el al IlJL)2). Peters, James I!I al and Stirnberg & Horn report that males are more commonly encountered than femal es.
12(,
Monitors of the World Ritual combat in this species is probably similar to that of other dwarf goannas. Dominant males will attempt to mate with subordinate animals of either sex (Bennett 1994a). Captive breeding has been reponed many times (e.g. Mudrach 1969, Stimberg & Horn 1981, Barlett 1982, Rese 1984, Eidenmuller & Horn 1985, Flugi 1990, Eiderunuller 1994). This little monitor can do well in very small enclosures. 0.5m2 of floor area is sufficient to house a pair, but these animals are often very intolerant of each other, especially in confined surroundings. In larger enclosures (e.g. 5m 2 of floor area) colonies of 6 or more adults can be housed together. Observations on captives housed outside (Bartlett 1982) suggest that given deep shelters they can tolerate temperatures as low as -6°C. Males appear to be very territorial, deterring intruders with bites to the neck, whilst females are allowed to move freely. In captivity these lizards thrive on insects dusted with vitamin and mineral powder with less · frequent feedings of small mammals or lizards. The enclosure should be as large as possible and a soft substrate provided to allow the animals to dig. Unfortunately distinguishing males from females is not easy because both sexes possess clusters of spiny scales at the edges of the vent. James el at (1992) suggest that females may reach a larger size than males. Eggs incubated at 27-31°C hatch after 72-107 days, but wanner temperatures result in fewer successful births and an incubation temperature of 27-290 C may be most suitable. Maximum clutch size is reported to be six (James el at 1992) but in captivity individual clutches never exceed four. However more than one clutch of eggs can be produced each year if the female has al:cess to sufficient food. Hatchlings measure 4.8-5.7cm SVL (l1-14cm TL) and weigh 2.1-3.6g. Given good conditions they can reach 18g within five months and attain sexual maturity within 18 months. Rates of water loss in Storr's goanna are similar to those reported for most other Australian varanids studied (i.e. 0. 12mg of water per cm2 of skin per hour at 30°C (Green & King I ~93). Sprackland (1980) noted that the colours of these animals become more intense during social interaaions and at higher temperatures. Animals housed in adjacent enclosures have been seen to wave their tails at each other (Wheeler, pers. comm.).
VARANUS TELENESTES Sprackland 1991 Russel Island monitor. Brandenberg (1983) noted that the populations of emerald monitors (Varanus prasinus) on some islands off western New Guinea did not differ ""~ markedly from those on the mainland. However 1'\ the isolated population on Rossel Island at the eastern tip of the Louisiade Archipelago were considered a new species by Sprackland (1990) and named Varanus leieneseles. It has a mottled rather than unpatterned underside and the enlarged scales on the soles of the feet are light rather than dark . Only a single specimen is known which measures 21.7cm SVL, 42.5cm TL. Nothing is known of its way of life.
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Little Book of Monitor Lizards
VARANUS TERJAE Sprackland 1991. 8lue-nosed guanna. Voranus teriae was described from animals previously assigned to Vprasinus by Czerchura (1980). It is believed to have a very restri l"lcd range of poss ibly less than 100km2 in the Iron and Mcllwraith ranges of the Cape York Penin sular in Queensland (McDonald et at '", IYY I). It is more heavily built than other monitors of the /JI"(l.l'int/.I' group and is distinguished by its corncaJ throat scales and unusual pattern. A co lour drawing is provided by Sprackland (1992). Near the Claudie River they have been seen foraging in leaf litter and on trees and are known to feed on inset:ts (orthopterans, roaches and beetles - Irwin I Y94).
VARANUS TIMORENSIS Timur munitur.
Gray 1836.
The Timor monitor is a little jewel of a lizard. Many SUbspecies have been described but all are now assigned to different species (i.e. V.timorellsis simi/is, V.timorel!sis scu/aris and V.rimoreJlsis orieJltalis). The Timor monitor lives on just a few small islands in the south of Indonesia; Timor, Sawu, Roti and Samoa/Seman/Kisser. It reaches a total length of about 60cm (25cm SV L) and has a tail 137-176% of the SVL. The heaviest recorded from the wild was 2YOg (Menens I Y5X; Brandenberg 1983; King 1993). Very little is known about the Timor monitor in the wild . They climb well and have been seen basking on fences around human habitations. When threatened they may take shelter on the ground or in trees. Like mo st dwarf monitors its diet consists of other reptiles (geckoes and small snakes) and invertebrates such as scorpions, orthopterans, spiders, mantids, bees and roaches (Schmutz & Horn 1986; Losos & Green 1888; King 1993). Aspects of ritual combat in this species are discussed in Horn (1985). The Timor monitor re spo nds well to good captive care and breeding has been recorded quite regularl y (Anon IYllO, Belcher 19110, Sautereau & Bitter 1980, Behrmann 1981, Rese 19X3; Moehn IYX4, Eidenilluller 19X6, Lambertz 1995). This species is not as robust as V.sca/aris and tends to come off worst when the two species are housed together (Murphy IY72). There are no spines around the vents of maJes to help di stinguish sexes (Mertens 1942b). An enclosure of 0.5m 2 is sufficient to house a pair, but ample climbing space should be provided with plenty of hiding places above ground. Timor monitors seem to tolerate each other weU and colonies can be maintained without much fighting providing, of course, suffic ielll space is availabl e. A diet of tiny rodents, egg yolk and insects is suitable, supplemented with vitamin and mineral supplements. Reproductive behaviour may be stimulated by introducing a 24 hour photoperiod (Anon I YXO). Even long term captives tend to lay eggs between December and March each year (when breeding is the wild is believed to take place). A single clutch of up to II eggs is produced, which hatch after Y3-1 X6 days depending on incubation
1211
Monitors of [he World temperature. Best results have been obtained at 27-30°C. Hatchlings measure 5.5-7cm SVL and weigh 4.5-6g. They can double in weight within 8 weeks.
VARANUS TRISTIS Mournful goanna, black-headed goanna, freckled
goanna, racehorse goanna. Varanus Irislis lristis Boulenger 1839 Varanus tristis orientalis Fry 1913. The mournful goanna is perhaps the most widespread of the Australian monitor lizards. It is found throughout the continent except for the extreme south and south-east and occurs on many northern islands. Christian (1981) reports that they are absent from Victoria and resuicted to arid parts of western New South Wales. Fitzgerald (1983) records a specimen from nonh-eastern New South Wales. According to Houston (1979) they are not well known in South Ausualia. Low (1978) records their presence on Magnetic Island off the northern coast of Queensland. Storr (1980) gives a list of locations in Western Australia and Maryan (1989) found them at Peak Charles. Western Auscralia. I visited Peak Charles in 1991 , a few months after an extensive fire , and could find no sign of them. Records of \lldslis oriellta/is in New Guinea and adjacent islands (Menens 1950) probably refer to the V.limorellsis type animals discussed previously. V.lrislis celliralis (Mertens 1957) is an obsolete name for V.lrislis orielltalis (Mertens J958).
·ti
The name mournful goanna is somewhat misleading. It refers to the entirely black colouration of the populations of V.lristis tristis around Perth, Western Ausualia (tristis = sad). Mournful goannas from warmer (i.e. more northern) areas become increasingly less sombre in appearance. The freckled goanna V.tristis orienta/is was described from animals collected on the Burnell River, Queensland. These animals lack the melanistic pattern of the mournful goannas and can funher be distinguished by the less spiny scales on the tail (Fry 1913; Mertens 195~). Storr (1980) remarked that the few specimens he examined from Queensland differed in scalation from Western Australian animals, but did not give details. In the literature therefore, animals without black colouration tend to be described as V.tristis orienla/is. The subspecies appear to be sympaoic in many areas and both are found on the eastern coast of Queensland (Christian 1981). Hatchlings of both varieties are brightly coloured, but freckled goannas retain most of their juvenile pallern whilst in mournful goannas the pallern darkens and is replaced with varying amounts of black as the animals grow. Mournful monitors reach a slightly larger size than freckled monitors (about 80cm TL vs. 60cm TL). In the deserts both sexes reach sexual maturity at 20cm SVL. A specimen 2'Jcm SVL weighed 307g, another 25cm SVL weighed 150g and a hatchling of 7cm SVL weighed just over 4g. The mournful monitor is an excellent climber. Where uees are available the lizards spend most of their time concealed beneath bark or in cree hollows. Where uees are absent, or are occupied by other species, the goannas will live in rock crevices or under slabs of stone. Fyfe (1<)7'J) note s that at Ayres Rock they are often seen around buildings. They are often found along ri vers and are known from forests, woodlands and scrublands but are also widespread in desens. They are probably absent from the rainforests. Little is known about their way of life in tropical Australia. 129
Little Book of Monitor Lizards
In the deserts of Western Australia mowllful goannas shelter in Eucalyprus trees and move directly from tree to tree, exploring burrows en route in search of food. They are most active during the spring and often cover over a kilometre per day accumulating large fat reserves to sustain them through six or seven months of inactivity during the winter. Other lizards are their main prey, including other goannas, skinks, geckoes and agamids. They often swaUow large agamids over a quarter of their own body weight and are able to swallow the heavily protected thorny devil, Moloch horridus. They also raid birds nests for eggs and Iledglings and collect a variety of invertebrates including orthopterans, beetles, ants and stick insects. Mating occurs in November, when pairs of lizards have been found sharing the same tree. Large numbers (6- I I but sometimes as many as 17) of small eggs are laid in December which hatch in February or March, when the adults are relatively inactive. Nothing is known of their nesting habits nor of the habits of juveniles, but very young specimens have been found considerable distances from trees (Pianka 1971 , 1982, 1994; Losos & Greene 1988; James, Losos & King 1992; Bennett 1993). The th ermoregulatory behaviour of the mournful goanna must be extraordinary. Body temperatures as high as 47.3°C hav e been recorded in the wild (Pianka 1994)! The ability to tolerate such high temperatures is very rare in the animal kingdom. In general however, mournful goannas maintain lower active body temperatures than other desert goannas. The amount of black colouration probably has a major effect on the rate of heating in thi s species. It would be very interesting to compare the thermoregulatory behaviour of melanistic and non-melanisti c forms. Outside the deserts mournful goannas may be less arboreal than their freckled counterparts. According to Christian (1981) the former is more suited to a terresnial existence than the latter, on accounts of its larger size and greater speed. In areas of Australia where they occur together Shine (1986) considered V.lriJtis to be less arboreal than V.scalaris and have a narrower range of habitats. Schmida (1985) listed the most important items of prey as frogs and small l11ammals. Swanson (1976) claimed that insects, mice and lizards are preferred foods. Both Christian (19R I) and Fyfe (1979, 1980) report that V.tristis can curl its tail over its head and body when basking or walking. The purpose of thi s unu sual behaviour is not understood . The name racehorse goanna has been used to describe several species of Australian monitor lizard, including V.tristis. This species may have most claim to the name, because they can move at phenomenal speeds, especially when they are very warm. Their speed, arboreal habits and secretive behaviour make them very difficult creatures to observe in the wild. Pianka ( I
130
", 1
. t}.
.
\
' .
~
Little Book of Monitor Lizards suitable, washed down with plenty of vitamins and minerals. Females should be gorged with food throu ghout the breeding season to enable them to produce large numbers of strong, healthy eggs. Darker animals in parti\:ular may benefit from cooler winters with a shorter photoperiod. Mating occurs in the spring and two clutches of eggs can be laid within a \:ouple of months and up to four c lutches can be produced over a year. They hatch after 95 137 days at 27 -29°C. Given good feeding (small insects and portions of rodents) they \:an u'iple in weight within three months and attain sexual maturity within 2 years.
VARANUS VARIUS Shaw 1790.
Lace goanna The la\:e goanna is the second largest lizard in Australia. It is widespread in eastern Queensland, eastern New South Wales and most of Victoria but is resu'iued to the extreme so uth-ea st of South Australia (Houston I'In). They also inhabit some islands off the eastern wast (e.g. Mackay 1959). Lace goannas will live wherever there are U'ees and are common in many areas (Kree ft 1886, Ric hardson 1976, Jenkins & Bartell 1980). Peters (1967) found them close to the middle of Sydney. Its habitat includes rainforest as well as many drier woodlands. As would be expected of such a ubiquitous lizard, its pattern varies between area s. A vividly banded form (sometimes known as V. varius beWi) is also found in parts of Queensland and New South Wales which lives alongside those of normal pattern. The ecological implications of the pattern change are unknown (but see Grundke & Grundke I <)'I2a). Horn's (I <)HO) suggestion that all banded animals are males has been discounted (Greer I <)X'I). In IXX6 Krefft suggested that lace goannas grow as large as 250cl11. None of this size exist now and specimens of 200cm TL are exceptional. A lizard from MalJacoota, Victoria meas ured 75cm SVL, l'I2cm TL and weighed 14kg (Weavers I <)H8). Another from Healesville was 198cm long and weighed almost 20.5kg. It was found to have eaten fo ur foxcubs, three young rabbits and three large lizards (Fleay 1950). In conu'ast, a large male caught by Stebbins & Barwick (I %8) in the spring measured 150cm TL and weighed 4.2kg. Males grow larger than females and probably have larger home ranges (Carter 1<)90). The lace goanna is a superb climber, equipped with massive strongly curved claws and can move through branches with great agility. Eggs and chicks of a large number of ground and tree nesting birds have been recorded as falling prey to the lace goanna (Lu\:as & Dudley I <)()<); Carter 1'124; Barrett 1928 Hindwood 1926: Gogerly 1922 Hyem 1'136; Broadbent 11)10; Goulburnite I 'lOX; Kaveny 195H). They may feed on birds to a greater extent than any other monitor lizard. Outside the nesting season a variety of mammals (including kangaroos, opossums and bats), snakes, lizards, turtle eggs, crocodile eggs , fish, spiders, snails and insect.> as small as ants are eaten (Krefft 1886, Vestjens 1977, Kennerso n 1980, Mansergh & Huxley 1'I~5, Webb 1982; Losos & Greene 198~; Webber 1993) . They will also eat carrion, even when it is in a very advanced state of decay (Kennerson 19XO, Ward & Carter 19~~ ) and will forage in human rubbish (Rose 1974). Krefft (1886) reported finding "several pounds of bones" in the stomach of one individual. Peters (1967) thought that the diet of adults was comprised largely of rodents and reptiles. Vincent ( l'Igl) suggested that lace gOJnnas feed purposely on berries.
132
Monitors of the World
The lace goanna is a very active lizard that searches for food both in trees and on the ground. When threatened they will invariable take shelter in the nearest tree and try to hide on the opposite side of the trunk as theiI aggressor. It seems likely that many large prey are caught after a chase over the ground. Horn (1981) found that males outnumber females by 8:1, but these animals are notoriously difficult to sex without internal examination. Ritual combat occurs in the typical bipedal manner (Twigg 1988; Horn et al 1994). In southern parts of Australia activity is reduced or halted during the cooler months. They shelter in burrows or tree hollows. Mating occurs during the summer in temperate regions. Up to six males may court a female at the same time and generally only the largest is successful (Wilson 1987). Mating has been observed taking place continuously over a period of several hours (Tasoulis 1983; Carter IlJ90). Maximum clutch size is usually given as 12 (e.g. Cogger 1959, Bustard 1970) and mean clutch size of 8 has been reported (Carter in Boylan 1995) but clutches of 19 eggs have been recovered from termite mounds (Boylan, 1995). Eggs usually weigh 50-65g (Bredl & Schwaner IlJ83, Horn 1991), representing a total possible clutch mass of over 1000g (but see below). The eggs are deposited in an active termite mound when these are available, either on the ground or in a tree (e.g. Longley 1945; Cogger 1959, Bustard 1970, Tasoulis 1992). In New South Wales eggs overwinter and hatch after 6-7 months. How the hatchlings escape from their tennite mounds has been a matter of some debate. They seem to lack the strength to break through the tough outer wall of the mound. Incidences of adult lace goannas excavating nests is high during the spring whilst the eggs are hatching and this behaviour may serve to release the youngsters (Carter 1989, Boylan 1995). However at present theiI is no published evidence that the maternal individual remembers the location of her nest and returns there after many months to release her young. A television documentary which purported to show the release of hatchlings from a termite mound by their mother used broad artistic license (Marven IlJ90). After their escape/release the youngsters may remain around the nest for a week or more before dispersing. Like other monitor lizards the youngsters are more arboreal in habit than the adults. Where termitaria are absent the eggs are deposited in burrows or possibly in hollow logs (Cogger 1959, Houston 1978). Lace monitors may remain in one area for most of their adult lives. Frauca (1966 in Greer 1989) records a spe<:imen that lived in the same tree for several years. Similarly females may use the same termite mound regularly as a nesting site. Where suitable termitaria are in short supply they may be vigourously defended against other females (Carter 1989, Hom 1991). The very large clutch of 19 eggs reported by Boylan (1993) could represent the eggs of more than one female. suggesting that nesting sites may be shared under some circumstances. Weavers ( I<)lHl) considered that in temperate areas lace goannas may reach great ages (well over 20 years), based on their extremely low growth rates. In captivity they are known to live for over 15 years (Flower 1937; Kennerson 1979). The thermal biology of the lace goanna has been investigated in some detail. They are able to raise their body temperatures by up to 2°C above ambient temperatures using heat generated by respiration (Bartholomew & Tucker 1964). Critical thermal maximums of 43-44.5 0 C have been established and below 5°C they are completely inactive (Spellerberg 1972). Green & King (19<)3) record activity temperatures of 32.8-36.4°C which can drop to about 21°C at night.
133
Little Book of Monitor Lizards Reproduction and artificial egg incubation have been reported by Markwell (1983) Bredl & Schwaner (1983) and Boylan (1995). Outside Australia only one captive breeding has been reported (Horn & Visser 1990, Horn 1991). An enclosure with at least 2.5m 2 of floor space is required to house an adult specimen. As much height as possible should be provided to allow climbing. Hoser (1993a) maintained a group of seven adults in a 90m 2 outdoor enclosure. Best results have been obtained with animals raised in captivity from an early age and originating from the same location. They do well on a mixed diet of insects, small mammals and birds with plenty of extra vitamins and minerals. Females may produce more than one clutch of eggs per year and need large amounts of food . Horn & Visser (1990) record that a female ate 15 chicks, 20 mice and 2 rats with a week of laying eggs! Pairs often tolerate each other very well , but separating and reintroducing animals may be necessary to trigger courtship behaviour. Larger animals will kill and consume smaller ones (Hoser 1993a). A nesting box (as described in Horn 1991) should be provided for the female to deposi t her eggs in. Depending on incubation temperature they hatch after 184-317 days (Markwell 191'13 , Bredl & Schwaner 1983). At a constant 29°C they hatc h after about 235 days (Horn & Visser 1989, Horn 1991). Youngsters measure 28-36cm TL and weigh about 35g, but significantly smaller hatchlings of 16-23g were recorded by Weavers (1988) and Boy lan (1995). It is not clear whether this is due to incubation conditions or related to the size of the female. Hatchlings seem to prefer vertebrate prey to insects and can grow rapidly, reaching 30cm S VL and over 300g within ten months (Horn 1991, Horn & Visser 1991). The environmental conditions provided for lace goannas must take into consideration the natural habitat of the animals, which varies from moist and tropical in the north to seasonal in the south.
VARANUS YEMENENSIS
Bohme, Joger & SchaHi
1'.Il19
Yemen monitor. The Yemen monitor was the most magnificent discovery of the IY80's. Specimens had been collected in the late I'hh Century and had been in the British Museum since 1'103 and 1906 but it had been presumed that the specimens had been mislabelled and must have been collected in Africa. Not until a Gennan film maker unwittingly filmed a large monitor lizard climbing a tree in Yemen was the scientific world alerted 10 the presence of this magnificent animal. For several years no living specimens could be found, despite intensive searches of their known habitat. Finally eight specimens were caught and brought to Europe, where the animals were declared a new species (Bohme elill 1'187 , Bohme elal 1989)., The Yemen monitor is similar in appearance to Valhigularis, especially to the eastern form Vlllhi!:ulilris microsliclus. It differs from the African lizards in its lack of pattern (except for a yellow band over the snout) and its smaller scales. Examination of blood proteins, hemipenal and lung morphology provide evidence that the Yemen monitor is a valid species (Bohme elill 1989, Bohme 1991 b, Becker 1991). The Yemen monitor reaches a total length of at leasl II0cm (5()cm SVL). This is a stoutly built species with a tail 108-120% of the SVL. They are known from the Yemen Arab
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Little Book of Monitor Lizards Republic, the Peoples Democratic Republic of Yemen and Saudi Arabia (all location data in Bohme el (II I':IX!))' where they live in scrubland and dry forest in the foothills of mountains up to at least I::lO() m above sea level. The Yemen monitor is most commonly seen (;Iose to shallow water or in dry river beds. Its diet is said to consist largely of insects (especially beetles), snails and other invertebrates. They probably take larger prey when the 0pp0rlunity arises. Activity may be reduced or suspended during the driest pan of the year (January to March). Despite the excitement over the discovery of this lizard there has been no rush of ecologists to Arabia to study it in its natural environment. In captivity the Yemen monitor appears rather to be a rather docile animal. Large males tend to dominate smaller ones and may prevent them from feeding properly. Behaviour similar to
mating has been observed between males but so far there are no record s of bipedal combat in thi s spec ies. When given the opporlunity they will dig deep burrows under a rock or tree stump (Honneger, pers. comm., Saegesser, pers. cOlnrn.). [n addition to invertebrates, the Yemen monitor will feed on mice, fish and birds in captivity (Bohme el at J 989) So far there are no rewrds of captive breeding.
Horn' s monitor (Romulus Whittaker)
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7
Keeping Monitors in Captivity
So far, this book has been primarily concerned with the lifestyles of monitor lizards in their natural environmenL~. Over the last 50 years vastly improved communications between continents and th e emergence of relatively cheap power in the forms of gas and electricity have made it possible to keep reptiles alive anywhere in the world. Monitor lizards are particularly rewarding animals to keep in captivity because of their intelligence and formidable appearance. But the size attained by many species, including almost all of the easily available monitors, mean that their success ful maintenance is dependant largely on the amount of space that is available to them. Providing they have adequate room to move, most are quite W1demanding creatures. Before discussing their care, a few words on the ethics and general principles of keeping wild animals in captivity are in order.
Keeping Monitors Successfully. The following chapters are dedicated to keeping monitor lizards successfuUy in captivity. "Sw.:cessfuUy" doe s not mean that the animals merely live a disease-free existence W1til old age causes their ultimate demise. It means th at all the functions of life are performed by the animals as they would be in nature, including reproduc tion . In my opinion, it is irresponsible to keep wild animals such as monitor lizards in captivity without at least attempting to breed them. Whilst keeping monitors alive in captivity, though not always an easy task, is one that is quite often accomplished, getting them to breed is still a rare occ urrence and as such, it is the ultimate challenge to all keepers of these magnificent creatures. Accord ing to CITES figures, trade in a minimum of 55,775 live monitor lizards was reported between lY75 and 1986. Between 1987 and 1993 the figure rose to over 270,000. This figure is probably a gross underestimate of the true numbers involved, but is nevertheless minuscule when compared with the Centre's figures for monitor skin and by-products (see Chapter 5). Unfortunately, the vast majority of live monitors exported to foreign countries fare no better than those exported as leather. Many die lingering death s in enclosures that are neither large nor warm enough. Many people find such treatment of wild animals to be as repugnant as slaughtering them for their skins. They have no co ntrol over the fate of animals in Africa or Asia, but they campaign actively at home to stop the sale of exotic animals as peL~, or even to outlaw the keeping of wild animals in captivity altogether. They argue that as well as being cruel the p racti se depletes wild popUlations, increases the risk of exotic esc apees becoming established and, when species perceived as being dangerous are involved, poses a threat to the general public. Their case is supported by a few unfortunate cases of foolishness and significantly mo re cases of neglecl. As far as monitor lizards are co ncerned , none of the species traded in large numbers appear to be under any threat, real o r potential, from the CITES regulated wildlife trade. Live specimens account for less than I % of the overall trade of animals and products made from them. It is true that an unacceptable number of specimens fare badly in captivity. This can be attributed to ignorance due to a lack of available information about their way of life in the wild and their care in captivity. The trade in live monitors creates small numbers of reliable jobs in some of the poorest parts of the world. It also ha s the potential to greatly facilitate studies of the animals in the wild . Thanks largely to the efforts of a few pioneers, it has been established that it is quite possible to breed monitor lizards in captivity providing a few basic criteria are met. There is still a great deal to be lea rned however and the threat of legis lation th at will prevent further progress is 136
Monitors in Captivity velY real in many places. The purpose of this book is to bridge the gap between general guides to the care of reptiles in captivity and detailed guides to the captive propagation of monitor lizards that, as yet, appear not to exist. What follows is based entirely upon my own opinions and many, more authoritative, readers may disagree with some of my comments.
Monitor Lizards & International Law. Nearly all councries are signatories of the CITES convention which concrols the trade in animals and plants considered to be vulnerable to commercial exploitation. All species of monitor lizard are afforded protection under this legislation. It is not lawful to transport the animals across international boundaries without a CITES export certificate from the country of origin and a CITES import certificate from the counoyof destination. In order to obtain these certificates you must satisfy the authorities that the animals are in your possession legally. Commercial trade in species listed on Appendix I of the CITES regulations is totally outlawed and permits only given for their export and import for other purposes under exceptional circumstances. Five Asian monitor lizards are included on Appendix I: the Komodo Dragon, Gray's monitor, the Bengal monitor, the Caspian monitor and the yellow monitor. All other species are listed in Appendix II. Commercial trade is allowed, but all specimens must carry CITES documentation. Failure to comply with CITES regulations results in automatic confiscation of the animals and punishments ranging from fines to imprisonment Buyers of monitor lizards should always get a copy of the CITES import certificate authorising their import. If the lizards subsequently breed and you want to sell the youngsters abroad you will be expected to prove that they are captive bred and that the parent animals were legally imported. Some countries, notably Australia, only rarely issue export permits for wild animals and never for commercial crade (however see Hoser (I 993b) for a fascinating account of the illicit crade in Auscralian wildlife). Goannas reach the rest of the world either for research and breeding exchanges between institutions, or illicitly. Luckily many specimens are intercepted at borders and passed on by the authorities to zoos and individuals who succeed in breeding them. Captive born Auscralian monitors with CITES certification fetch very high prices. In addition to CITES regulations local laws may impose separate rescrictions or even prohibitions on the import and keeping of certain monitor lizards.
Monitors as Pets. The Shorter Oxford English Dictionary defines a pet as "any animal that is domesticated or tamed and kept as a favourite, or treated with fondness". Monitor lizards can certainly not be domesticated. If you allow one the run of your home it will cause untold damage without showing the slightest remorse. If you let it out of the house it is highly unlikely that it will ever come back of its own accord. They can be tamed in as much as some individuals will eventually learn to tolerate gentle handling without showing aggression (especially when deprived of sunshine and fresh air), but expecting them to obey any commands, or show the slightest affinity for anything but other monitor lizards is unreasonable. Monitor lizards are ancient, intelligent and beautiful creatures capable of living "happily" in captivity for many years, but to describe them as pet animals would be misleading.
Safety. Monitor lizards survive by catching, killing and defending themselves against other animals. Therefore they are equipped with sharp teeth, strong jaws and powerful claws. Only adults of a few, very large, species have the potential to inflict serious injuries on people but all monitors can inflict scarring wounds and they should always be treated with caution. The
137
Little Book of Monitor Lizards most common wounds infli(;ted by monitor lizards are scratches to wrists and forearms whilst the animals are being handled. The tail is used as a whip in defence and (;an be mobilised with great speed and for(;e. But the jaws are of the greatest concern. They sink through flesh to the bone and then shake with all their might. Handling wild animals is not something you can learn from a book. Herpetological societies always have members who are happy to share their expertise. Wild monitors should not be handled without a pair of stout gloves that afford protection to the wrists . They should be seized from above by grabbing the back of the head and the base of the tail in one movement, so that the lizards cannot turn to bite. Obviously very large specimens should be restrained with a noose and require more than one person to lift them. Lifting the lizards by the tail is a very bad practi se that can resu lt in injury to either party. Animals kept inside are often much more do(;ile than those kept in open air. Ditmars (1910) records an incident in which some very docile water monitors were moved outside for the sUlTuner whereupon they immediately reverted to their wild 'state, attacking their keeper at every opportunity. Once deprived of fresh air and sunshine they soon became placid and friendly again.
"Taming" Monitors. Well-kept monitor lizards do not require any grooming. If their toenails become too long and need to be (;ut this should be taken as an indication that the furnishings in the enclosure are unsuitable. Dead skin should come off of its own accord. [f it needs to be pulled off this indicates that some environmental parameter (probably humidity) is in(;orrect. Some of the people who have had most su(;cess with breeding monitor lizards consider it important that the animals do not get used to being handled and are allowed plenty of privacy. One obvious reason for this is that monitor lizards show their dominance to weaker individuals by rubbing their backs or lying on tOP of them. A monitor lizard that is handled in this way assumes the role of a subordinate animal and may be less likely to initiate or respond to courtship. However, in the family environment the lizard keeper may feel that it is in their interests that the lizards tolerate gentle handling by themselves, their parents or their children. The irrational fear of reptiles experienced by many unfortunate people often vanishes when they touch one and reali se that it is warm and dry rather than slimy and cold. When monitor lizards are used to being handled they are much less inclined to struggle and bite. [ndividuals used to humanity from a early age are sometimes extremely docile. The process of taming some monitor species is neither dangerous nor difficult if the animals are obtained as juveniles. [ndividual monitor lizards have very different temperaments and many will become pla(;id, almost friendly , in human company. However is not a total guarantee of safety, and large specimens should be treated with caution at all times, regardless of their disposition . The monitor keeper who is admitted to hospital as a result of his or her carelessness does little to enhance the popular perception of reptiles. To I
13X
Monitors in Captivity
Abo ve & Oppo site (top): Correct way to hold a small or medium monitor (MJ.Bennett) Oppo site (bottom): [ncorrect way to hold a large monitor. The left hand should grip the back of the head from above. Even thick gloves do not protect wrists against fearsome claws. 13lJ
SPJI!Zl1 J01IUOlAJ
JO '1008 :lPJll
Monitors in Captivity
Never handle a monitor while it is digesting large meals and never attempt to tame large animals unac<.:ustomed to people. The more they are handled as youngsters, the tamer they will be as adults, but it is important to continue to handle the monitor regularly throughout its life, lest it forgets. Very large monitor lizards have the potential to inflict horrendous injuries and they should always be treated with caution. All monitors react to smell, and approaching a large male whilst bearing the scent of a rival could give you more than you bargained for.
THE VIRTUES OF CLEANLINESS In the wild monitor lizards are hosts to a multitude of internal "parasites" (e.g. Jones 1988 & 1991; Bos<.:h 1991). Many of them are hannless only because they are present in small numbers. The stress induced by capture and transport often allows these organisms to propagate to such an extent that they destroy their host. Therefore a newly imported monitor should be subjected to the scrutiny of a vet and treated with drugs to kill any potential pathogens that live inside it. When the lizard is free from harmful parasites and bacteria the object is to keep it that way with s<.:rupulous attention to hygiene. Newly acquired specimens should be subjected to a strict period of quarantine W1til veterinary examination confirms that they are free from parasites. Only when the lizards have been proved to be healthy should they be moved into the vicinity of established animals.
THE PROBLEM OF SPACE A myth, that is extraordinarily common considering its stupidity, is that an animal "wiU grow to the size of its surroundings, and then stop"! This, of course, is utter nonsense. A healthy reptile never stops growing, from the day it is laid to the day it dies. Many monitor lizards spend most of the day fast asleep, and may not initially appear to very active animals. However when they do move they tend to wver a lot of distance. Typical daily forays for even dwarf monitors may be in excess of 200m per day and many monitors typically walk several kilometres in an afternoon. Obviously it is not possible to provide this amount of space for captives and it has been demonstrated that many species will do well in remarkably small enclosures. The term "small" is relative however. Captive lizards become lethargic in cramped surroundings for several reasons: I. Thermoregulatory behaviour. Normal lizard behaviour involves movement from areas of one temperature to a wanner or cooler environment in order to maintain a preferred body temperature. In small enclosures the temperature is uniform and the lizards cannot alter their body temperatures significantly by moving. A large enclosure, on the other hand, may contain a range of temperatures, from 18-44 oC for example. This gives the lizards the opportunity to sele<.:t a body temperature that suits them and alter it at will. A small enclosure heated to 44°C would kill the inhabitants very rapidly. 2. Foraging. Monitor lizards do not swallow huge meals and then go to sleep for six months. They spend most of their active time searching for food; in leaf litter, under cow dWlg, underwater , on the branches of trees, in burrows, termite mounds, rock crevices, abandoned buildings etc., usually finding only small invertebrates. They also learn very quickly and a monitor kept in a small space quickly realises that there is nothing worth foraging for and stops looking. Larger, well-planned endosures may always contain concealed food items and promote more normal activity patterns.
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Littl e Book of Monitor Lizards Prospective purchasers of a baby water monitor usually fail to comprehend that the little brightly-colow'ed lizard in the pet shop will soon grow into a formidable carnivore so mewhere between two and three metres long and quite capable of putting its owner into hospital should it feel thus inclined. There is no reason why these animals should not be kept safely and successfully if their basic needs are met, and space is of primary imponance. Large terrariums are inconvenient because of the space they take up and can be expensive to keep warm. Nevertheless with careful planning they can be made unobtru sive and costS can be minimised. In the accounts of monitor lizard species given in Chapter 6 I have cited the smallest known enclosure in which the animal s are known to have reproduced. A few of them are impossibly big and relate to animals kept outside in the tropics but most are a reasonable size. A general rule for the larger species (i.e. those not belonging to the subgenus Odatria - see Chapter 2) is that the enclosure should be at least three times as long and rwice as wide as the total length of the lizard at maximum size, mea sured from the tip of the tail to the tip of the snout. This allows them at least moderate space in which to move. An adult trio ca n be hou sed in em:losures of these sizes so long as ample basking and hiding places are provided. Arboreal species also need to be provided with a taU enclosure that allows them to climb at least their own body length above the ground. Monitor lizards grow so quickly that it is usually not se nsible to have to build successively bigger enclosures as they increase in size. Dwarf monitors appear to need much less space than their larger counterparts. Many will live long lives in areas of less than I m2 if adequate furni shings are provided. If space reall y is a problem, and the unfonunate creature is already in your possession, then it is better to try to tame the animal and give it the run of the house rather than keep it in a cramped terrarium. As long as they are provided with a suitable source of heat they should regulate their behaviour around keeping warm. Some monitors continually seek out the coldest pans of a room and lie there immobile for days or weeks. I presume that this is related to the need for an annual period of inactivity. Often they will conceal themselves somew here that makes them very difficult to retrieve. It would be very foolish to allow a large untamed monitor lizard to wander about the house. Even tame ones will destroy your furniture.
HOUSIN(;. Outside. Wherever the climate will allow monitor lizards should be housed outside, where they will greatly benefit from increased space avail able, the sunshine and the fre sh air. The local range of temperature and air humidity are the factors that must be taken into consideration when deciding whether to try an outdoor enclosure. The tolerance of monitor lizards to cool northern climates is not well documented. A number of spec ies (i.e. V.albigularis, v'niloricu.l. V.griseus. V.bengalensis. Vj1avirufus. v'rosenbergi and v'varius) ex perience cold winter s tn at least pan of their range. The lizards maintain a satisfac tory body temperature by remaining in deep burrows which remain surprisingly warm. There is no reason why they should not be kept outside and provided with heated shelters. at least during the warmer parts of th e year. Tropical species are unlikely to take kindly to temperate climates in any season. Elaborate precautions need to be taken both to sto p the animals escaping and to prevent the entry of cats and wild animal s. Monitor lizard s are excellent diggers and so the enclosure 142
Monitors in Captivity should have a very hard bottom, otherwise the walls need to extend underground for at least I m to prevent them escaping. The walls should be smooth to prevent the lizards from climbing over the top. If the lizards can climb a tree and leap to freedom they will certainly do it. Care must also be taken to ensure that the lizards do not consume any poisonous animals, including slugs and insects treated with pesticides. Sheets of corrugated metal designed for roofing provide an economical fence if they are riveted together and fixed finnly in the ground. Insulated "kennels" are the easiest way to provide warmth and sl!elter in outdoor enclosures. Burrows are liable to flooding and forbid access to the lizards without excavation. The kennel is typically a wooden box covered with a thick layer of polystyrene and a waterproof coating (e.g. asphalt). It should have a single entrance via some sort of tunnel to reduce heat loss and be provided with a source of drinking water. It need only be large enough to allow the lizards to curl up inside and can be heated with an electric greenhouse heater or a soil warming cable to provide a temperature of about 18°C to which the animals can retire at any time. In cool weather the animals can be shut in the kennels. When the lizards are first housed outside only heated shelters should be available to them. This eliminates the danger of them being unable to locate a source of warmth in cold weather and becoming stupefied. Once the animals are acquainted with their kennels unheated retreats can be provided with impunity. Plenty of shade from the sun and elevated basking platforms must also be provided. Supplementary basking heat can be provided with a waterproof spotlamp. Water should be plentiful and small pools, just large enough for the lizards to immerse themselves, can easily be constructed by lining a hole with several sheets of butyl rubber. Pools for large heavily clawed animals must be tougher; fibreglass moulds or concrete are more suitable. The more decadent enthusiast may consider installing a pool heater. The furnishings of the enclosure are limited only by the imagination. Rock piles, caves, trees and waterfalls are just some of the options that are not usually available in an indoor terrarium. Indoors. Sadly, in most parts of the world the swnmers are too short and mild to make outdoor enclosures worthwhile and the lizards must be kept inside in large heated boxes. Once constructed the box should be in place for over a decade, so careful planning at the outset is highly desirable. The shape of a monitor terrarium depends on the habits of the species to be housed, as well as any aesthetic or practical considerations. The most important factor is that it should be as spacious as possible. The importance of providing monitor lizards with adequate space has been mentioned before, but it needs to be reiterated. Many large snakes can be kept successfully in very small enclosures, but this is never true of the monitor lizards. They will not thrive in a cramped environment; they are unable to thermoregulate properly, become weak, lethargic and obese and their resistance to disease is lowered.
MATERIALS FOR THE ENCLOSURE Unfortunately, few, if any, of the dealers who sell monitor lizards also sell enclosures large enough to keep them in! For this reason it is necessary to employ the services of a builder or carpenter, or construct the terrarium oneself. The important qualities of the enclosure are that it be easy to keep clean, well ventilated, strong enough to withstand repeated attempts to escape and have good heat retaining properties. Enclosures for aquatic monitors must also be waterproof. A variety of materials are suitable, just a few of which are described below. Members of your local herpetological society will doubtless be able to suggest many more. 143
Little Book of Monitor Lizards Ideally all terrariums will have some sort of drain on the floor that facilitates cleaning and prevents the substrate getting waterlogged. A false bottom in part of the enclosure can also be useful. The enclosure must be well ventilated and provision for fans and vents should be made during construction. The simplest and best enclosure for large monitor lizards is an unused room, ideally a cellar. Attics suffer from massive temperature changes and can become incredibly hot on a summer afternoon and very cold at night. Very careful attention to heating and ventilation is required in such enclosures. Large monitor lizards can tear plasterboard walls apart like wet cardboard and it is usually easier to build a large enclosure rather than allowing them the run of the room. Brick and concrete are often used to make homes for the giant monitors. Their main disadvantage is that once built they are difficult to dismantle, but given the great ages reached by varanids it should be many years before this becomes a problem. The benefits of these materials are recogni sed by everyone who lives in them ; to all intents and purposes they last for ever, are immensely strong, retain heat well and can be built to any size and shape required. Glass is expensive and nOl1Tlally is used only for the front of the enclosure. The price of glass of the size and strength needed to contain most varanids would make the cost of an all glass terrarium astronomical. Second hand window frames (with or without glass) are ideal for incorporation into larger enclosures and can often be obtained very cheaply. Frames with cracked panes are useless unless the glass can be replaced entirely. Large monitor lizards have been known to smash through extremely expensive armoured glass. Aquariums make good homes for hatchlings and for dwarf lizards. Their main disadvantage is that they tend to be very narrow and tanks over 50cm wide usually have to be made to order. Large aquariums make ideal enclosures for smaller amphibious monitors such as V.mertellSi. especially when additional "dry land" is also provided. Hatchling monitor lizards grow at such a phenomenal rate that they must be moved from the aquarium into more spacious quarters after a very short time. There are some excellent flbreglass and plastic terrariums on the market. which are made especially for reptiles. but they are not available in sizes suitable for most monitor lizards. Fa<.:tories may be able to supply large moulded tanks which can be adapted to make suitable enclosures but they are likely to be expensive. Look under "glass fibre" and "plastic" in the yellow pages and enquire about imperfect products. which may be available at much lower prices. Alternatively cement and plaster can be used to build the walls of the enclosure and the inside can be coated with a mixture of sand and epoxy resin, making a very strong, waterproof finish that is aesthetically pleasing. Wood is widely available and relatively cheap. It can be used to make enclosures of virtually any size or shape. The usual choice is a simple wooden box which can be knocked together by almost anybody. Laminated chipboard (particleboard) is one of the best materials for small and medium sized monitors: it is relatively inexpensive. easy to keep clean. is available in large sizes makes a strong terrarium if constructed correctly and can be made waterproof with a few coats of liquid rubber or polyurethane varnish. The construction of a very simple <.:hipboard enclosure is outlined in Appendix V but the best source of infol1Tlation is the local Herpetological Society. Reptile keepers are often ingenious in their approach to building terraria and are always happy to pass on advice.
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Monitors in Captivity When a monitor lizard is free from disease it is possible to keep it that way by keeping its enclosure and furnishings scrupulously clean. This means periodically (every few months) taking the enclosure apart and disinfecting it. Therefore the furnishings used should be either easy to clean or cheap to replace. SUBSTRATE Great care should be taken when deciding what substrate your lizards will live on. Unsuitable substrates may make it difficult for the lizards to walk nonnally and can cause irritations of the skin, particularly under the feet. Because almost all species love to dig they should be provided with at least some areas of soft substrate. The main disadvantage of soft substrates is that they are more difficult to keep clean than floorings such as tiles and newspaper, which can simply be lifted out and scrubbed or replaced. However their advantages to the lizards' well-being make it well worthwhile taking extra trouble to remove all traces of fecal material as soon as they appear. Some keepers object to soft substrates on the grounds that the lizards tend to swallow particles along with their food. In the wild monitor lizards almost always have bits of debris in their stomachs including sand, gravel, soil and bits of wood. It appears to pass through them without causing any mishap, but because ingestion of large amounts of some substrates can be injurious, sharp sands and gravels should be excluded from the terrarium. The choice of substrate depends on the natural habitat of the species concerned. For desert species sand is the obvious choice. The type used should be fine and free from sharp edges. Builders' sand is not suitable and neither are most gravels. Sand can be dug up or bought from a garden centre. If collected in seashore areas it should be rinsed free from salt. For most other species a substrate of a mixture of sand and leaf mould or bark chippings is ideal. Avoid peat and other dusty substrates that become airborne when dry because they tend to cause respiratory problems. There are various artificial substrates available which are made especially for terrariums, but they are very expensive in the quantities nonnally required for monitors. Eidenmuller (1986) suggests that cat litter makes an ideal substrate for some smaller species. Regardless of the substrate used it need be no more than 15-30cm deep if artificial burrows are provided. Large volumes of substrate are unstable unless held together by plant roots so big monitors are best prevented from digging deep burrows in order to eliminate the dangers of them collapsing and burying the lizards alive. Generally monitors prefer to steal burrows of other animals rather than go to the trouble of digging them The type of substrate used and its ability to retain moisture will have an important effect on the humidity of the enclosure. For species that like high humidity the substrate can be kept damp and the rate of evaporation increased by gently heating the substrate with a mat or a cable. Even for desert species it is a good idea to spray the sand with a little water several times each week, so that the lower layers are always slightly damp. In temporary quarters (such as quarantine) newspaper or corrugated cardboard make the best substrate as they can be replaced every day. They are unsuitable for everyday use because they do not afford the lizards a good grip, and are soon ripped to shreds by energetic digging behaviour. Cork tiles can also be used. They have the advantage of affording the lizards good grip whilst still being easy to clean and replace. Paving stones make an excellent substrate for rock dwelling monitors.
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Little Book of Monitor Lizards Gravity ensures that most of the bacteria in the enclosure live on the boltom and great care must be taken to ensure that all traces of faeces are removed from the terrarium as soon as they appear.
FURNISHINGS The furnishings in the enclosure provide the lizards with 0pp0rlumtles to hide, bask and search for food. They appreciate a variety of different surfaces to climb on and because stone and wood heat at different rates their use helps maintain the thermal gradients essential to nonnal behaviour patterns. The furnishings greatly increase the surface area available to the lizards for activity and should be chosen with care.
Stone Stone absorbs heat slowly and retains it well. Judicious use of rocks in the enclosure is of central importance in establishing the thermal gradients required. Avoid those with sharp edges or that crumble when scrubbed - granite and hard sandstone are good choices. Tree dwelling species which have only stone to climb on tend to wear their claws down faster than they can grow and the number of rocks used in the enclosure depends on the habits of the animals to be housed . In some cases a single large stone is sufficient, situated close to the basking lamp, where it will continue to emit heat long after the lamp has turned off. For rock dwelling species the enclosure should resemble a quarry. The bottom and sides of' the terrarium can be partly covered with thin slabs of stone to which additional pieces can be cemented to create numerous caves, ledges and overhangs for the lizards to explore. They may also appreciate large elevated blocks of stone. Rock s used on the floor of the enclosure should be heavy and have flat bases. Rock piles should be firmly cemented together, if rocks are piled on top of each other the lizard s will eventually dislodge them. A plastic hide box covered with rocks provides a very simple cave. Wood Branches are esse ntial for monitor lizards that like to climb. A walk through a wood will usually yield many suitable pieces of tree stump and branch. Only take hard, dead wood that ha s already become separated from its tree. Avoid decaying branches and those that might ooze sap or resin. Make sure that all branches and stumps are secure and can not be shifted by the lizards. Careful use of branches can greatly increase the available area of the enclosure. Monitors from jungles and thick forests prefer to climb a mongst a tangle of branches but those from more open area s can do well with ju st a few large branches to rest on. Small tree-dwelling monitors very much appreciate the shelter afforded by hollow branches and will generally sq ueeze into the smallest shelter that will accommodate them. In high enclosures beware of the fact that lizards may leap from the highest branch to the ground and reduce the risk of injury by providing a so ft substrate below. Smaller species greatly appreciate the use of cork tiles on the sides of the enclosure, which gives them even more climbing surfaces. For larger climbing species the walls should be covered with planks of wood to which bark is still anached.
Shelters Monitor lizards need to be provided with plenty of dark retreats to help them feel secure. Many keepers are inclined to be stingy with hiding places because they rarely see their lizards otherwise. Thi s is a mistake. Given adequate space most monitors eventually loose most of their nervou sness after prolonged periods in captivity, but if they are not able to conceal
146
Monitors in Captivity themselves when they feel threatened they will never acclimatise properly. Many keepers have found that elevating the enclosure a metre or so above the ground has a dramatic effect in reducing the timidity of the lizards. In the wild monitor lizards shelter in burrows, termite mounds, rock crevices, tree hollows, in dense vegetation or under stones. These shelters are used not only to escape from predators but to reduce water loss and maintain suitable body temperatures when conditions are inclement. Similar shelters must be provided in captivity. Monitor lizards are very strong, and if they can dismantle the furnishings in the enclosure they will do so. All rocks and wood must be fastened securely to prevent risk of injury by minor landslides and tree falls. Providing adeq uate hiding places is particularly important when several animals are kept together. The smaller ones will greatly appreciate retreats that the larger ones are unable to enter. Many species like to wedge themselves into very tight spaces, and careful planning is required if you require immediate access to the lizards without recourse to a sa w or crowbar.. Artificial burrows can easily be constructed by building a false floor into the terrarium with a hole cut out of one corner to which a piece of pipe is attached . The pipe can be sealed at one end, or left open to give the lizard a large subterranean chamber. which should also be covered with substrate. Alternatively artificial burrows can simply be buried in the substrate. Monitors prefer to dig or steal a burrow situated close to tree roots or rock s, so suitable furnishings should be arranged around the edge. Hollow branches are utilised by many monitor lizards who feel secure only above the ground. Finding narural branches of a suitable size and shape may not be very easy, but nestboxes similar to those sold for birds provide a good alternative. A number of shelters of different sizes should be offered and some should be positioned as high as the enclosure will aUow. Rock crevices and caves are the usual hiding places of many species. If heavy stones are used great care must be taken to ensure that there is no danger of collapse. Alternatively artifi cial retreatS can be made by carving out blocks of polystyrene (styrofoam) to a suitable shape and coating them in a mixrure of sand and epoxy resin. Furnishings made in this way can be made to resemble simple caves or be as complex as termite mounds.
Basking Surfaces Monitor lizards appear to select basking areas with great care. Some prefer to bask on wood or stone, others se lect exposed areas of ground. In all cases bas king sites are somewhat elevated. In the terrarium a variety of furni shings should initially be provided around the heat source to determine the lizards' preferences (see below). Stone can get very hot when exposed to heat but some lizards like to bask on surfaces that are uncomfortably hot to the touch. Wood and organic substrates do not reach such high temperatures and may be preferred by other animals. Each arumal housed must have access to suitable basking areas and great care mu st be taken to ensure that the lizards cannot burn themselves on a heat source. Imagine the animal trying to burn itSelf by jumping at the heater, or standing on itS hind legs and trying to touch it with its tongue, and position the equipment accordingly.
CONTROL OF THE ENVIRONMENT. No monitor lizard lives in an environment that never changes and most experience significant flucruations in humidity, temperature and daylength over the year that have a profound effect on their behaviour. It is desirable to reproduce some of these seasonal changes in captivity in
147
Lillie Book of Monitor Lizards order to allow the lizards to approximate their natural cycles, but extremes must be avoided. Lizards that are forced to spend seven months of the year underground in their natural habitat do not necessarily benefit from having to do the same in captivity. Allowing some monitors to undergo periods of reduced or suspended activity appears to be essential for their well-being and reproducing seasonal changes in light and/or rainfall patterns can always be seen to have a beneficial effect. Working from the premise that in order to keep monitor lizards successfully every attempt must be made to reproduce their natural envirorunent it is obvious that careful attention needs to be given to simulating the natural cycles of the year as they occur in the animals' home countries. To this end data on temperature and rainfall in different areas of the world in inhabited by monitor lizards are given in Appendix III. They can be used in conjunction with data on daylength (e.g. Jones 1978) to reproduce seasonal changes but they are given as a guide only and must be used with great caution. The charts show the average temperatures recorded at meteorological stations in areas inhabited by monitor lizard s. They do not show the temperatures experienced by the lizards, who carefully se lect cooler or warmer microclimates according to their inclination. The literal use of this data to determine the heat of the terrarium would often result in the death of its inhabitants.
HEAT Monitor lizards appear to show great variation in their thennoregulatory behaviour. Some species like to maintain a relatively stable body temperature whilst others like to get hot during the day and cool down at night. Even within small popUlations, individuals show a great deal of variation in their preferred temperatures. Monitors regulate their temperature largely by moving to warmer or cooler microhabitats and so during the day the enclosure must accommodate a thermal gradient that includes both hot basking areas and much cooler retreats. Ideally the temperature of the enclosure should reflect the range experienced by the lizards in the wild . This varies enormously between species. In many parts of the tropics the nights are scarcely cooler than the days and there is little seasonal fluctuation. Elsewhere temperatures may drop sharply at rtight and for most of the year the weather may be too hot or too cold to allow much activity. By installing an efficient heating system in the terrarium the lizards are given the opportunity to thermoregulate naturally and seasonal changes ca n be approximated. Of course all heating elements, thermostat sensors and wires must be positioned where the lizards cannot touch them. Any connections that could conceivably get damp should be sealed in epoxy resin.
Heat Gradients. We have seen that monitor lizards' behaviour is determined largely by thermoregulatory considerations and that artimals with no control over their own body temperature tend to be lethargic. The enclosure therefore must be heated in a way that provides a variety of temperatures in a relatively small space. They must have access to substantial heat (above 40°C, sometimes as high as 50°C) for part of the day and always have plenty of cooler retreats available. High temperatures enable the lizards to digest their food quickly and thoroughly and promote rapid growth and good health. However, the basking area should account for only a small part of the enclosure and burrows or other shelters, situated as far from the heat sources as possible, must be provided. This is most important, because although low temperatures kill reptiles slowly, excess heat is rapidly fatal. All the monitors studied to date die when their body temperatures reach about 41 °C. Monitors that are too hot show it by panting (a normal behaviour) and gasping (in extreme cases when death is near). In a well planned terrarium, where a variety of temperatures are available. it is
14S
Little Book of Monitor Lizards impossible for the lizards to overheat, because they simply move to a cooler area when desired. To establish a good thermal gradient several maximum-minimum thermometers should be placed around the enclosure and the position of fumishings and heat sources altered until an acceptable variety of temperatures is achieved.
Primary heat suurces The purpose of the primary heater is to provide a source of constant warmth both day and night that prevents the lizards from getting too cold, and so it must be powerful enough to keep the enclosure suffidently warm during even the coldest weather. The simplest way to heat small and medium sized enclosures is with one or more ceramic heaters, controlled with an electronic thermostat to give precise control over the temperature. These are easily obtained from reptile dealers. Methods of heating such as mats and cables, which are designed to fit at the bottom of the terrarium are unsuitable for large monitors unless they can be positioned so that the animals cannot dig them up. If many terraria are kept together it is usually more economical to heat the entire room. Enclosures for large monitor lizards require more powerful heaters which can be powered by gas or electricity. A local heating specialist should be able to suggest an efficient and economic system which must be highly controllable and free from all fumes or smell. The minimum temperature should be a year round 25°C for tropical species and 12-20-
Secundary heat sources The purpose of the secondary heat source is to provide the lizards with "hot spots" or basking areas during the day, so that they can regulate their own temperature as they do in the wild. There mu st be a basking spot available for each animal in the enclosure, or the weaker monitors will be deprived and unable to thermoregulate. The basking areas below the heat source should be planned with care. Some species like to bask on a platform above the ground such as a branch or a large flat stone, whilst others prefer to lie flat on the ground in an area cleared of debri s. Depending on the species to be kept, either stone, wood or bare substrate can be used for the basking platform. Be sure to position all heat sources where the lizards cannot burn themselves, even if they try. Retlector-type parabolic spotlights are the usual choice for the secondary heat source. The harsh glare of spotlights can be reduced by positioning them at the front of the enclosure and directing them towards the back. Bigger enclosures may benefit from the use of an infra-red bulb that generates more heat without producing visible light However monitor lizards often associate heat with light. and invisible infra red heaters are responsible for most of the serious burns that are incurred by captive specimens. Therefore particular care must be taken to ensure that it is impossible for the lizards to injure themselves when heat sources of this type are uti lised. The wattage needed will depend on the distance between the heat source and the basking ;]re;] and heat absorbing properties of the basking surface. Pick one strong enough to keep the hottest basking surfaces between 40-4!l°C. Some individual lizards may find this too hot (others will happily bask at even higher temperatures for short periods). but in a well planned terrarium they will be able to select cooler basking sites. A thermostat should be attached to the heat source to prevent the enclosure from overheating in warm weather.
14<)
Little Book of Monitor Lizards f)aily Variations in Temperature For tropical spet:ies the night-time temperature should not be more than a degree or two lower than the ambient temperature maintained during the day. For many temperate dwelling monitors. espet:ially desert species. a more substantial drop in temperature at night is benefidal. Seasonal Variations in Temperature When naturally seasonal lizards from temperate climates are kept at temperatures that permit year-round activity they may suffer in a number of ways. They may become obese or conversely may waste away and die. Without a period of inactivity it may be impossible for their reproductive organs to mature. Some temperate species mate almost immediately after their period of hibernation. During the previous months the reproductive organs have become at:live and the large fat deposits accumulated by females are turned into eggs whilst the males have expended much less energy on the production of sperm. A period of a few months inactivity therefore seems to be desirable. However exposing captive monitor lizards to periods of hibernation is a risky business at best. Very little is known about the body temperatures maintained by wild monitor lizards during cold weather and at present providing temperatures at which the lizards should be kept during artificial hibernation would be purely speculative. Many animals that enter hibernation apparently healthy emerge from it very poorly and sometimes they may fail to emerge from it at all. Maintaining the lizards at too warm a temperature would result in them slowly wasting away rather than entering a state of true hibernation whilst the use of a temperature that is too cold would kill them outright. Because so little is known about this subject I recommend that you do not consider letting the animals hibernate unless you have the guidance of somebody with experience of the practice - try the herpetological society. However an annual period during which temperatures are reduced and the lizards become less active may be beneficial for many species. In some cases maintaining the animals at temperatures cooler than normal for a period of just a few days may trigger reproductive activity. Only well nourished. perfectly healthy animals that are known to have originated in a temperate climate should be treated in this way. The animals should be fed well for several months prior to cooling and the basking periods reduced a month or so before turning off all of the lights and allowing the animals to rest. Minimum ambient temperature can be allowed to drop as low as 12°C at night and need be no higher than 170C during most of the day. The lizards will become immobile or sluggish but providing they are in good health to begin with and the period of cooling does not exceed 10-12 weeks no problems should result (be warned however that cooling the lizards will inevitably subject them to some stress and that this can lead to an impairment in their ability to ward off disease).
LIGHT If the enclosure can be positioned where it receives some natural sunlight, without exposing it to draughts or excessive heat, so much the better. But sunlight looses much of its spectrum when passed through glass and because light of a suitable spectrum and intensity is essential to the lizards' well-being it is necessary to invest in a lighting system that imitates the spectrum of sunlight The cheapest are fluorescent tubes that do not generate heat and run at low wattages. A full spectrum tube such as "Vitalite" provides all necessary wavelengths including ultra-violet which is essential for many lizards to synthesize vitamin 0 1 , Ultra·violet radiation can be injurious to the eyes and lights are only effective when the li~ard and bulb are in close proximity. You should check this with the manufacturer. Not everyone is convinced that monitor lizards need a source of ultra-violet light if they are supplied with
150
Monitors in Captivity adequate Dl as a dietary supplement. Other lamps reproduce the sun's spectrum without producing u·ltra-violet light. More expensive options are mercury vapour lamps which give a very faithful rendition of natural sunlight and generate heat as well. Tungsten light bulbs and white fluorescent tubes are very poor substitutes. A wide variety of light sources available and prices vary considerably, so it is wise to ask around (especially at your local herpetological society meetings) before making any expensive commitments Providing light of the correct intensity is as important as providing a natural spectrum. The intensity of light experienced by monitor lizards in the wild varies between species; the large eyes of many rainforest dwellers suggests that they live in relative gloom compared to those exposed to the harsh desert sun. Whilst there is no doubt that changes in photoperiod are important for many monitor lizards there is, as yet, no such evidence that changes in light intensity are of any con5e(juence. Seasonal Variations in Day Length In many animals (and plants) changes in daylength are responsible for triggering a variety of responses including initiation of changes in physiology related to breeding and hibernation. Even around the equator, where daylength only varies by a few minutes throughout the year, changes in photoperiod may have a major influence on the lizards' behaviour and physiologies. For this reason it is a very good idea to expose captive animals to proper photoperiods. This is easily done with a simple timeswitch that can be progranuned to go on in the morning and off in the evening. More expensive devices also allow a period of dawn and dusk that maybe beneficial to some species. By altering the photoperiod by a few minutes each week a natural cycle can be followed. Ideally the cycle used should follow the seasons as experienced in the animals' home country rather than locally. With animals from another hemisphere however this often proves inconvenient because the lights will be on longer in the winter than in the summer. Best success has been obtained by maintaining natural cycles but many people believe that if young animals are obtained they should have no problems adapting to a reversal in light cycles. Seasonal changes in light intensity can also be replicated by the use of additional lamps or bulbs of a higher wattage. Data on daylength and elevation of the sun in different parts of the world are given by Jones (1978). Although the term daylength is used here, the important factor is often the duration of the hours of darkness. therefore at night the lizards should be shielded from peripheral light sources. There is no evidence that monitor lizards are influenced by lunar cycles to any great extent. WATER Drinking Water Monitor lizards vary greatly in their exposure to water in the wild. Some rarely encounter it whilst others never stray from it. Although many monitor lizards survive in the wild without ever drinking, a source of freshwater should always be provided for captives. However many monitor lizards, particularly desert species, will happily spend so much time emersed in water that their flesh begins to rot away. For this reason many people recommend that either the water receptacle for monitors from arid areas be too small to allow the animals to wallow, or else water should be provided just once a week. Eidenmuller (1993) notes that providing water for a short period each week, with the addition of a soluble vitamin supplement, helps ensure that the animals do not suffer from dietary deficiencies. Desert monitors are superbly adapted to conse~ing water but many aquatic species loose water at an incredible rate, and (hey must have constant access to a freshwater supply. 151
Little Book of Monitor Li7.ards
For monitors other than aquatic species, water is best provided in a heavy container that cannot be overturned. Some arboreal species (such as the emerald monitor) may prefer to drink above the ground, in which case a small water container should be sel:urely attal:hed In a branch. Some monitors may prefer to drink water from rocks or leaves. in whkh l:Jse a
Humidity The humidity of the air in the enclosure is a very important consideration. Tropical forest dwelling lizards experience much higher levels of humidity than do those from more open. temperate areas. In general a relative humidity of 60-70% is suitable for temperate spel:ies. whilst those from tropical forests need a humidity of 75-R5%. Seasonal fluctuations in humidity are common in the wild, with the highest levels achieved during times when both temperature and rainfall are high. The humidity can be measured with a simple hygrometer available from gardening shops. Pools or drinking bowls placed close to the heat source will generate significant humidity whilst misting the enclosure with a fine spray of water helps maintain suitable humidity levels. This is of benefit to all species during at least part of the year. Enclosures for monitors requiring very humid conditions must be waterproof and may have to contain drains in the bottom. Pools All monitors will immerse themselves if given the opportunity and many species not associated with water in the wild will spend long periods in it in captivity. Over long perioos of time this can lead to fungal infections that eat away at the animals' appendages. Pools are only necessary for monitors that habitually spend time submerged in the wild. Although water monitors have been bred in set-ups with only small drinking bowls, the animals tend be more secure and less nervous if they can submerge themselves. For highly aquatic species (such as Mertens' goanna and the mangrove monitor) water should account for most of the volume of the enclowre. A pool can be fitted into the false bottom of the enclosure to minimise splashes. The simplest way to make them is to use a fibreglass mould available from garden centres. Large pools require separate heating, usually by means of a submersible heater and thermostat of the type used for aquariums. A temperature of 20-28OC is suitable. All pools need very regular cleaning and the water should be replaced at least several times per week. Many monitor lizards can be given the occasional run of the bath, which is particularly beneficial during skin-shedding.
152
Monitors in Captivity Simulated Rainfall It is often beneficial to simulate rainfall. especially for tropical varanids. In order to do this the bottom of the enclosure must be fitted with a drain. Ideally the bottom of the enclosure can be made of mesh and the water collected in a large receptacle below (that must be emptied daily). The simplest way of simulating rainfall is to use a small aquarium water pump attached to a very fine spray bar. Special misters and automatic raining devices can be obtained from some reptile dealers. The water used should be 25-30 oC and free from chlorine It is unnecessary to drench the lizards with litres of water, 10-20 minute showers are sufficient. Hot light bulbs often explode when splashed with water. VENTILATION The air in the enclosure must be replaced regularly, so the ventilator must allow the movement of air without also causing cold draughts. The simplest ventilation systems are grills Illade of metal or plastic which can be built into the top or sides of the enclosure and closed when desired. Electrically powered extractor fans are better for large enclosures which have a greater volume of air to move. Regardless of the method used, the air which is drawn into the enclosure must not be so cold that it causes a drop of more than a few degrees in the ambient temperature, nor should it alter the humidity to any great extent. For best heat efficiency the ventilators should be situated as far from the secondary heat source as possible. It is very simple to set an electric fan on a time switch, so that it comes on for just a few minutes each hour.
DIET Providing high quality food for monitor lizards is unquestionably one of the most important factors in their successful care. The diets of monitor lizards are very varied in the wild. Many are opportunistic feeders that will eat any animal they are able to overpower but most feed mainly from two or three classes of prey. The studies conducted to date show that most of the food eaten by even the large monitors is comparatively small. Of course the animals' diet in the wild does not indicate their preferred choice, merely what is available. A monitor looking for large prey such as crabs will come across many smaller animals such as insect~ in its search. As a result the bulk of its diet may be the smaller animals which are encountered in the search for larger prey. When larger animals are abundant they make more efficient foods. because they offer more nutrition for less energy expenditure. Monitors are intelligent reptiles and in captivity they quickly become used to certain foods and will ignore others that are less sustaining. or are too much trouble to catch or eat. Most published accounts of monitors reproducing in captivity relate to animals which have been fed a diet comprising almost exclusively of rats, mice and chicks, and there is not enough data available to detennine how much difference a more varied diet would make. However the rarity of captive breedings indicate that more attention should be given to the animals' lifestyles in the wild, and certainly the diets of free living monitors are drastically different to those provided for most captive specimens. Wherever possible the lizards should be given a varied diet which includes animals of the prey types known to be taken in the wild. Most foods can be offered alive but it may be necessary to give the lizards only dead birds and mammals to keep on the right side of the law. Captive monitors kept on a diet of large animals often ignore smaller foods (Kaufman el al 19<)4), including those that form the bulk of their prey in the wild, and it is very likely that this laziness is detrimental to the lizards' well· being. After visiting many zoos and private keepers to ask questions and photograph their animals, an eminent monitor breeder was kind enough to invite me to his house. Virtually all of the captive varanids I had photographed previously were either extremely shy or else indifferent to my efforts, but the 153
Little Book of Monitor Lizards first specimen I attempted to photograph here. a rather young sand goanna. behaved in a way
which I was not at all prepared for, despite the warnings of my learned friend. After several
flicks of the tongue it emerged from its retreat. launched itself at me. seized my finger and
made a most laudable attempt to amputate it. Since then I have seen the same vigollrolls
behaviour. albeit from a slightly greater distance. in many groups of well-kept captives. all of
which reproduced. I have no doubt that careful feeding plays a major role in the successful
maintenance of these animals and that, after neglect of initial parasitic infestations.
overfeeding is the main cause of premature demise and failure in attempts to breed monitor
lizards in captivity.
Ideally all prey items will have been raised in captivity but in practise many suitable food
animals may be available locally. Before taking them it is imperative to ensure that it is legal
to do so and that the animals are not contaminated with poisons or disease harmful to the
monitor lizards. Never take more animals from the wild than are needed to satisfy the li zards'
immediate needs.
No ellpense should be spared when raising animals destined to be fed to monitor lizards.
They should be fed only' fresh foods and kept under the best conditions possible. For
guidance on breeding insects, rodents, snails and other suitable prey items you should consult
members of your local herpetological society. With the ellception of Gray's monitor (whose
diet in captivity is discussed in Chapter ti). plants do not figure in the diets of monitor lizards.
Vitamins and Minerals
The regular use of good vitamin and mineral supplements is indispensable. Feeding monitors
on a varied diet should, in theory, provide all the nutrients, vitamins and minerals required for
good growth and health. But vitamin and mineral deficiencies are very common in captive
monitor lizards, even when they are housed under ideal conditions and their prey animals are
reared on ambrosial fodder. Hom & Visser (1990) suggest that monitor lizards increase their
mineral input by rubbing their prey into the ground before consuming it. All food items
should contain supplements and many people find the use of soluble vitamins in drinking
water to be advantageous. Invertebrates can be dusted with vitamin and mineral powders
whilst dead vertebrates can be injected with liquid supplements. The micro-nutritional
requirements of reptiles are complell and beyond the scope of this work (an ellcellent
discussion of the subject can doubtless be found in Frye (1991). A surfeit of certain vitamins
(particularly A and D1) and minerals are known to cause problems. but in general monitor
lizards are not prone to health problems associated with the overuse of supplements.
providing suitable ones are chosen. A bewildering variety of vitamin and mineral supplements
are available. many made specially for reptiles and all containing slightly different proportions
of different micronutrients. Balance between calcium and phosphorus is particularly
important. The most authoritative works on breeding monitor lizards in captivity recommend
the use of vitamin and mineral supplements with aU food items and suggest the use of a
cakium:phosphorus ratio of 2: 1. (Horn & Visser 1990; Eidenmuller 1992).
Insects
Insects make up the most important part of the diet of many monitors in the wild and should
fonn the staple diet of most species in captivity. Their movements trigger the monitors'
predatory natures and because they are difficult to catch they make the lizards work for their
food, sometimes the only ellercise lethargic specimens ever have. Crickets. locusts.
grasshoppers. cicadas. butterflies. moths. beetles. cockroaches. mantids. stick insects.
154
Monitors in Captivity maggot s. June bugs and beetles will be accepted by many monitors. Some of these foods can be cultured but many suitable insects will be available locaJly at different times of year. When foods are collected from the wild you should ensure that they have not been exposed to pesticides and that you are not collecting protected species. Monitor lizards can eat large amounts of insects in a single meal which would be impossible to collect outside in any season. They can be bought locally or obtained by mail order but the cheapest and most reliable option is usually to breed them at home. Many initial attempts at breeding crickets result in mass escapes that make further attempts impossible due to household hostility. If the crickets escape outside during warm weather they may serenade the neighbourhood for the rest of the summer. Therefore. colonies should be housed in a very deep, smooth sided containers and kept well covered. One of the best orthopterans to breed for monitor lizards is the black cricket. Gryl/us bimaculatus. Unfortunately its song is not as melodic as that of the less nutritious members of its family. but it is a large meaty insect that few lizards can resist Many exotic invertebrates are available through the post from entomological suppliers and a few of them may be inexpensive enough for occasional inclusion in the diet. An excellent food for monitor lizards is the Argentinean wood cockroach (Blabtica dubia) . They reach a large size (adults can weigh up to 5g) and are easy to keep and breed (providing the temperature never falls below I SoC). Although considered unsightly by many people. this large insect cannot fly. nor can it climb smooth surfaces, making escapes unlikely. They can be obtained from entomological suppliers, or from other reptile keepers. There is little or no danger of introducing disease with insect prey (although they are known to act as vectors of disease in wild monitors (e.g. Mackerras 1962», but many insects and invertebrates are poisonous to some animals. and so their use should be avoided . They include centipedes. millipedes, scorpions. spiders, and many insect larvae. Although all these creatures are preyed upon in the wild there is no guarantee that monitors are immune to the poisons of alien species. All invertebrate prey should be dusted with a vitamin and mineral supplement just before they are fed to the monitors.
Other invertebrates A wide variety of land and water dwelling molluscs and crustaceans are devoured with relish by many monitors. With the possible exception of the slugs and snails none can be propagated. so they must be bought or collected. Slugs. snails. crabs and crayfish can often be found locally. More exotic species such as giant African land snaiJs and hermit crabs are available from some pet shops. The shells of molluscs and crustaceans present no difficulties to monitor lizards. SmaU prey are swallowed intact whilst the larger ones are crushed and their shells discarded or swallowed separately. Saltwater crabs and molluscs should only be offered to lizards that are known to eat marine organisms in the wild and can therefore tolerate high salt intake. Earthworms make a good food for many monitors and are very easy to collect. Mammals Rodents. rabbits and other manunals make excellent foods for most monitors lizards, but they should not be used to the exclusion of other prey types. Domestic varieties of many manunaJs are inexpensive. widely available and very easy to breed. However. some insectivorous and molluscivorous monitors seem unable to cope with large amounts of fur in their diets and their use as food for these species should be restricted to the occasional treat. Manunals should be fed sparingly to all monitor lizards because if overused it may be difficult to get
155
Little Book of Monitor Lizards them to aCl:ept the other foods essential to their health. Very small monitor lizards offered chopped up portions of baby rodents.
(all
he
Reptile keepers have a bad reputation with rodent keepers, and it appears that the latter rarely impart their knowledge to the former. Mice and rats will live anywhere and eat almost anything, but those destined to become reptile food should be treated with partil:ular compassion. They should be given sufficient space, kept dean and warm, and fed 011 the finest foods available. Even then their corpses should be injected with vitamin supplements just prior to use . Frozen rodents can be bought in bulk from some biological suppliers and thawed out when required but is unwise to use animals that have been frozen for over six weeks as food and, if available, freshly killed foods are always to be preferred. Night time walks down l:ountry roads often yield an abundance of fresh car victims. They make perfectly al:\;eptable foods as long as there is no danger that the animals have been exposed to poisons. Using live mammals to feed monitor lizards is probably unnecessary, because the lizards "kill" dead food before swallowing it and therefore seem unable to tell the difference. Furthermore there is always the chance of an indignant rat biting back and causing serious injuries
Rirds and their Eggs . Most monitors will eat birds, ranging in size from day-old budgerigars to adult ducks and chickens. They should not be collected from the wild, but obtained through hatcheries, bird breeders or butchers .. Vitamin and mineral supplements should be injected into the body cavity of dead prey animals before they are given to the lizards. Eggs make a good occasional food for many monitor lizards. Smaller specimens may crack the shel.ls and let the contents run down their throats. whilst larger ones will swallow them whole. There is some danger of Salmonella infections with many farmed eggs which can be eliminated by boiling them until the yolks set. although this doubtless compromises their nutritional value. Fish Many monitors. including those not normally thought of as aquatic. are very partial to fishes. Many species of fish from the fishmonger are suitable as occasional foods for monitor lizards known to feed around seashores. They include trout, whitebait. herrings and mackerel. Freshwater fishes (such as goldfish and tropical species such as cichlids. barbs and rainbowfish) can be fed to all monitor lizards. Fish with sharp spines (which are often invisible) are unsuitable because they are adept at lodging themselves in their predators' throats. Livebearing fish such as platys and swordtails are ideal. because they are easy to keep and breed at home. Reptiles and Amphibians Although monitors eat many reptiles and amphibians in their natural environment~, wildcaught animals cannot be recommended as food for captive varanids because of the very real possibility of disease transmission. On the other hand frogs. lizards and snakes which have been bred in captivity make good food. so long as they are known to be disease free. In practise it may prove very difficult to obtain sufficient quantities of animals to forma regular part of the monitors' diel~. The best amphibians for use as monitor food are the frogs of the genus Rana. especially the European common frog (Rana temporiaria) and the north America bullfrog (R. caresbeiana). Both of these animals can be easily propagated and are extremely prolific. Although some monitors are known to prey on toads, the toxins of unfamiliar species may prove fatal, so they are not a suitable food . The same applies to a few frogs. Both the yellow monitor and the rough-necked monitor are known to eat amphibian 156
Monitors in Captivity eggs in the wild, but whether they would do so in captivity is unknown. Tunles and their eggs are eaten with great enthusiasm by monitors in the wild. but because of the dangers of amoebit: infections they cannot be recommended as food for captives. All lizards and snakes wi" be eaten by monitor lizards. Cenain species of geckoes, skinks. anoles and garter snakes are available at low prices, so captive bred specimens are readily available. However the dangers of passing on disease by introducing unquarantined reptiles and amphibians (dead or alive) into the monitor enclosure cannot be overestimated and only animals known to be free from disease should be used ..
Unsuitable Foods Monitors should be fed whole fresh animals whenever possible. Processed meats, offal and meat derivatives such as mince and dogfood are very poor and messy substitutes for the real thing . Great care must be taken to ensure that the monitor lizards do not eat food animals that have been treated with pesticides or other hazardous chemicals. Animals that appear sick or wasted should not be offered. Poor quality, intensively farmed foods (particularly birds and their eggs) pose a risk of Salmonella and other food poisonings. Some processed foods are sold specifically for feeding to carnivorous lizards, but I am unaware of any reports of t:aptive breeding in monitors maintained on such a diet
Frequency and Quantity of Food Juvenile monitor lizards have enormous appetites. grow very quickly and should be given as mut:h food as they will eat. As their growth rate slows however their appetites remain undiminished. As adults many species become prone to obesity in captivity. Most monitor lizards (probably all of them) are able to store huge amounts of fat in the body and around the base of the tail. If they eat more food than they need fat continues to accumulate until it bewmes detrimental to their health. Obese animals are unlikely to reproduce and are much more prone to disease and earlier demise than those of normal weights. Obesity is seen least often in animals that are fed a diet containing plenty of invenebrate prey and is usually most ex treme in seasonal species deprived of their annual period of reduced activity. Furthermore, males may be more prone to obesity than females. In some species of monitor lizards fat reserves are used in different ways by the sexes. In nature, females' fat reserves are sometimes used to produce eggs whilst males expend very little energy in sperm production and expend most energy during the mating season. In captivity, whilst females may be able to produt:e eggs unhindered, the males' ability to search for mates and fight off rivals is severely limited. Bet:ause of this females should be fed more generously than males, especially prior to and after reproduction.
It is imposs ible to give precise details of the optimum weight and amount of food required by adults , because these parameters are influenced by many factors. Where known, the weights of free living animals of different lengths are given in Chapter 6, but this provides only a very rough guide. In the wild monitors' weights fluctuate from season to season and it may be net:essary to reprodut:e this pattern in order to maintain the animals successfully. In general, inset:ts and other small invertebrates should be offered to the lizards at least several times per week, whilst vertebrate prey are given less often (once per week or fortnight). However some monitors will not be satisfied with this, whilst it may cause others to put on too much weight. Small meals provided regularly are better than large meals given at longer intervals, and t:arerul attention should be given to the condition of the animal and their food intake adjusted at:cordingly. It may be possible to cure some obese animals with careful feeding.
157
Little Book of Monitor Lizards Feeding Problems. Initially. wild-caught monitor lizards are often reluctant to feed in captivity. They should he offered as wide a choice of prey animals as possible in the hope that something will stimulate their appetites. Adult lizards in good condition are quite able to withstand periods of fasting of a month or so, but if the fast persists much longer action should be taken. Force feeding an animal that has refused to feed for some time may be of little value. because the food is simply regurgitated rather than digested. Regular injections of amino acids and minerals often help the lizards to recover. Veterinary supervision is highly recommended. Sometimes a monitor lizard that appears to be healthy will suddf'nly refuse to eat. Oflen this is related to their need for a period of reduced activity each year. Lizarrls used to periods of inactivity in the wild may go off foorl altogether despite the provision of favourable environmental conrlitions. As long as the lizarrls are not maintainerl at too high a temperature anrl rio not become emaciated. long fasts are not dangerous, but a loss of interest in food may he a sign of rlisease. A lack of suitable light is often cited as a reason for loss of appetite in reptiles. If the enclosure is illuminated with cheap light bulbs now is the time to change them for more expensive light sources that imitate the sun's spectrum. If rlisease is suspecterl the animal shoulrl be taken to a vet for examination. [f lizards from temperate environments arc still fasting afler a month, rlespite the new lights, and the vet can finrl no sign of illness. it may be wise to reduce the ambient temperature of the enclosure by several rlegrees anrl allow the lizarrls to become inactive for a few weeks. Any animals that become very thin shoulrl be force ferl as rlescribed above. Often an animal that refuses to feed can be tempted eventually by offering a wirle range of prey items. Once the lizarrls begin to feed they become less fussy about the foorl they take, and soon accept the usual monitor fare. Heavily gravid females are often unable to eat because they are literally stuffed with eggs. If neither eggs nor appetite have appearerl after a month veterinary advice must be obtained. The only feeding problem experienced by many monitor lizards in captivity is that they get too much of it.
mSF.ASF. Unfortunately, the diseases of monitor lizards are many anrl the cures are few (Kohler 1992: Stanfill 1995). The good news is that once an imported monitor is cleared of disease. it should be possible to keep it that way by keeping its enclosure and furnishings clean and avoiding any contact with sources of contamination such as wild foods and other reptiles whose health is suspect or unknown. The bad news is that wild-caught monitor lizards always harbour parasites that have the potential to destroy their host, especially when they have been subjected to the stress of capture and shipment For this reason all new monitors should be carefully quarantined until they are determined to be free from disease. This means keeping them in a separate room in a regularly sterilised enclosure used solely for this purpose. These organisms noed to be identified and destroyed by a qualified vet. The presence of most serious parasites can be identified from samples of blood and faeces and are treated with a variety of drugs. Obviously it would be very foolish to attempt to diagnose and treat the diseases of tropical reptiles without professional help. More and more vets are developing an interest in exotic wildlife and most herpetological societies or zoos will recommend a specialist. Vets are very well trained and in the best position to diagnose disease and prescribe cures but it may be necessary to haggle hard over their fees. The use of do-it-yourself guides to the diagnosis and cure of reptile diseases cannot be recommended. Until animals have been pronounced free from infection by the vet they should be isolated from all other animals. Clinical standards of hygiene are required in the quarantine enclosure. 15R
Monitors in Captivity It should be well isolated from all other terrariums and only contain furnishings that can be sterilised. In all other respects it should be designed in the same manner as other terrariums and the lizards supplied with adequate space. light, heat, food, hiding places etc. Newly imported monitor lizards are often particularly nervous and this stress further weakens their ability to withstand disease. As far a possible the animals should be left undisturbed.
Careful quarantine and early elimination of potential pathogens by an expert is the key to keeping monitor lizards healthy. Thereafter they should remain healthy providing that their basic needs (good diet, correct temperatures and humidity, freedom from stress) are met and they are not exposed to infection from other reptiles whose health is suspect. A study of cause of death in 248 monitor lizards concluded that almost half had died as the result of infections (Kohler 1988). Whenever a monitor lizards appears to be ill it should be isolated immediately and the advice of an vet obtained without delay. To be on the safe side it is wise to have even long term captives screened for parasites by a vet every year or so. As well as internal parasites monitors are host to a many external parasites that attach themselves to the lizards' skins and suck their juices. Some lizard ticks are very beautiful and their ecology is fascinating (e.g. Hesse 1985, Auffenberg & Auffenberg 1990), but in captivity they must be regarded solely as vectors of disease. They should be dabbed with alcohol and removed with tweezers, taking care not to pull off the bodies and leave the mouthparts embedded in the lizard. lf ticks spread to other lizards it may be necessary to destroy them with insecticides, for which veterinary advice should be obtained. Obviously it makes sense only to buy healthy aninnals in the fust place. Obtaining young captive bred animals is ideal, but at present wild caught specinnens are usually the only available option for most species. As in ali walks of life there are a number of disreputable characters who are not adverse to selling animals which they know have no chance of survival. Again, members of your local herpetological society will probably be happy to pinpoint the rogue dealers and recommend those that are honest and conscientious. Purchasing animals without seeing them fust is asking for trouble unless you are buying them from a dealer whose reputation is unblemished. No matter how honest your supplier, inevitably some species of monitor lizard are very heavily infested with parasites when they arrive at their final destination. Most have the potential to survive for long periods in captivity if they are still strong and receive immediate veterinary care, but most untreated specinnens are doomed within weeks, and Doctor Dolittle himself would be unable to save them. When buying a monitor lizard it should be examined very carefully. Particular points to look for include; I. The monitor should be lively rather than lethargic. It should be very interested in food, be able to hold its body off the floor, walk normaliy and be observed to protrude its tongue. Newly imported specinnens should struggle vigourously when handled. Missing toes and taiJ tips are not a serious problem except in highly arboreal species such as the New Guinea tree monitors. 2. There should be no sores, lumps or bums on the body or tail. Look underneath, in the folds of skin at the in sertion of the limbs with the body and pay particular attention to the shape of the spine. There should be no sign of swelling in any of the limbs.
159
Little Book of Monitor Lizards
3.0pen the mouth and look for signs of rot or parasites, refuse any whose breath smells rancid 4. The eyes should be clear and not bloodshot, the nostrils should be dry and free from any discharge.
s.
There should be a finn deposit of fat at the base of the tail. Absence of fat does not necessarily indicate disease however. Specimens captured just after a period of inactivity or females after oviposition often appear somewhat emaciated.
o.
Breathing should be unlaboured; Wheezing, coughing and sneezing are early signs of respiratory infections.
An animal offered for sale which shows any untoward symptoms should be refused . Sadly, once monitor lizards have succumbed to infections they do not often recover. It is much better to leave them to die in the shop than to buy them and encourage the proprietor to get more. Wise dealers have monitor lizards screened for major parasites as soon as they are imported, and add the bill to the animals' price. Even so they should still be subjected to a normal period of quarantine after purch ase.
LIFESPAN There are very few records of the longevity of monitor lizards in captivity (Flower InS, IY37, Snider & Bowler 1992, Bennett 1994) and virtually none of their lifespan in the wild. The record appears to be held by the Taronga Zoo in Sydney, where a Komodo dragon was kept for 24.5 years. The animal was adult when acquired, and a total lifespan of about SO years has been predicted for this species (Auffenberg 1981). The Tel Aviv University Zoo maintained an adult desert monitor for 17 years, and estimated its age at death as at least 25 years. Other large monitors lizards are reco rded as surviving for 20 years or more in captivity. Unfortunately there is much less infonnation available on the lifespan of the dwarf monitor lizards. A female spotted tree goanna kept at the Basel Zoo in Switzerland was still laying eggs after 20 years in captivity (Bennett 1994b). Of course, the reported figures tend to be exceptions rather than the norm but they do indicate that a life expectancy of at least a decade is not unreasonable and that many specimens of both large and small species can live for at east twice as long. Monitor lizards therefore, although they do not attain the great ages recorded for crocodilians and chelonians, are amongst the most long lived of the sq uamate s. Co nsideling that most species can attain sexual maturity within three years it can be seen that the reproductive potential of these animals is enonnous and that females of the more prolific species may be able to produce more than 500 eggs in a lifetime. Unfortunately this potential has not yet been realised in captivity.
16U
8
Breeding Monitors in Captivity
Breeding monitor lizards in captivity is still an exceptional occurrence. Many species have never reproduced outside their natural range and consistent reproduction over several years is still almost unknown amongst the larger members of the family. Luckily many of the people who succeed in breeding their animals take the time to write down their experiences for the benefit of others. Unluckily (for the linguistically-inept inhabitants of the English speaking world) the vast majority of the literature on breeding varanids is in German. Translations of some works can be obtained from the SSAR (address in Appendix I).
()btaining a male and female Obviously in order to attempt to breed monitor lizards it is necessary to have at least one male and one female. Unfortunately they are notoriously difficult animals to sex. In a few dwarf species males have spines at the sides of the vent which are only weakly developed or absent in females, but in at least one species (Storr's goanna) the spines are present in both sexes. Sex determination by differing scale characteristics around the vent has been described for the Komodo dragon and the Bengal monitor (Auffenberg 1981, Yadov & Rana 19!!!!). In both of these species and many others males are reported to grow larger than females and the males of many African and Asian species develop bulbous snouts towards old age. These phenomena are of little practical use when trying to determine the sexes of wild caught animals whose ages are unknown, because obviously a four year old female will be larger than a two year old male. The males of some species are said to have wider heads or thicker tail bases than the females and although there is no reason to doubt this, such criteria are of limited use when animals from different locations and of unknown age are concerned. Sex of monitor lizards is often determined on the basis of hernipenal eversion (notably in field studies in which the animals are not sacrificed). Wild animals unaccustomed to being handled often evert their hernipenes when being manipulated. If the hernipenes are totally everted then the animal is considered a male. But if eversion is only partial it is impossible to distinguish the male hernipenes from the similar structures everted by the females', unless equipped with a very good knowledge of the differences in their morphology. Furthermore, an animal that does not evert its hernipenes cannot definitely be considered a female. It might be an uncooperative or not particularly weU endowed male. Immature animals do not evert their hemipenes and once the lizards have been handled a few times they generally stop displaying this behaviour. Acclimatised adults can sometimes be induced to evert their sex organs by spraying the vent with tepid water; otherwise hold the monitor upside down, push the tail down and apply gentle rolling pressure with the thumb over the vent, from back to front. Again, this may serve to determine the sex of some males with certainty but great caution must be exercised when interpreting the results from animals that fail to evert completely.
'S~ e Ze igler & Bohllle (1'1<)5).
161
Breeding Monitors in Captivity A number of more intrusive methods to detect hemipenes have been devised. A common method. used to sex many reptiles, is to probe very gently inside the vent with a lubricated. blunt. metal instrument (Honneger 1978). In theory, the probe will extend further in males than in females. The problems with this method are that most monitor lizards are too strong to allow the probes to be inserted without risk of damage. many females probe almost as deeply as males and the lizards appear to find the process extremely unpleasant. This is a method that can only be learned by direct observation of someone with experience. Other methods that are designed to forcibly evert the hemipenes require professional expertise (e.g. Balsai 1992). In general it is best not to interfere with your lizards' genitals. Another method of sexing monitors is to use x-rays to detect mineralisation in the hemipenes (Shea & Reddacliff 1986. Card & Kluge 1995). A vet can do this by rinsing the vent with a barium solution or dye and taking an image at about 57.5kV. 125mA for 0.04 seconds or 40kV. 25m A for 0.6 seconds. This method has been shown to be effective in many species but not in Bosc·s. Bengal, grey, Mertens', Nile, rough-necked, water and Timor monitors. Nor does it work with young animals. Also it is not clear from the literature whether the opaque material is definitely missing in females. The most reliable method of sexing monitor lizards is by endoscopic examination (Schildger 1'1 al 1993, Schildger & Wicker 1992). This can only be done by a vet and involves
anaesthetising the animal, making a small hole in its body wall, inflating the body cavity with gas and viewing the ovaries or testes through an endoscope. In the hands of an expert this procedure looks very simple. The examination may also reveal internal disorders that would otherwise go undetected until manifesting themselves as sickness. Again this method may be ineffective when applied to young animals, but when used on adults it is virtually infallible. Because male monitor lizards are more active than females they tend to be caught more easily, and as a result females are often more difficult to obtain. Because at present there is no easy way of sexing most monitors with 100% accuracy, the best policy to ensure the presence of a pair is to obtain about half a dozen young monitors. allow them to grow up with alternating periods of solitary and group confinement (if they will tolerate each other) and try to deduce their sex by their behaviour towards one another. Unfortunately there are few obvious sex-specific behaviours in monitor lizards. Males often attempt to mate with each other and animals of both sexes will engage in ritual combat There are many other good reasons why juvenile animals are to be preferred. They adjust better to life in captivity, are less likely to be loaded with dangerous parasites and if cared for properly will live for at least a decade. Usually it is not possible to determine where a captive animal originated. This is unfortunate because some species have enormous ranges and specimens from very different habitats may prove incompatible. This is especially true of Bengal, Nile, mangrove, desert, water and white-throated monitors. Reports seem to indicate that breeding has occurred between some "subspecies" of monitor lizard. but it is not known whether fertile offspring were produced. Ideally the potential breeding stock will not be very closely related (e.g. brother and sister).
Conditioning the animals The second prerequisite for breeding is that the monitors are in reproductive condition. In nature most monitor lizards are only reproductively active for part of the year. The ovaries and testes increase in size towards the beginning of the breeding season and shrink 162
Breeding Monitors in Captivity afterwards. The timing of mating, and egglaying are determined by rigourous selection that ensures that both sexes are sexually active at the same time of year and that the timing of breeding and length of incubation provide the youngsters with the best possible chance of survival. Control of the maturation of reproductive organs is under the control of hormones. The stimuli that cause the release of these hormones is not always clear, but in many animals .:hanges in daylength are a major factor (Chapter 7). A period of inactivity or reduced activity may be ne.:essary to allow eggs and sperm to develop. By attempting to imitate the environmental conditions experienced by the lizards in the wild the chances of breeding are maximised (Chapter 7). Females need plenty of top quality food with plenty of vitamin and mineral supplemenl~ in order to produce healthy eggs, but there may be no change in her outward appearance until after the eggs have been fertilised and the only way to tell if the lizards are in breeding condition is by their behaviour towards each other. I~ousing
Monitors together
Once the animals have been conditioned they must be coerced into mating with each other. Often it is difficult to house the pair of lizards together for long enough to ensure fertilisation of the eggs without one killing the other in the process. If immature specimens are obtained and can be reared together they may pair off naturally without undue violence. Often it proves beneficial to keep the animals separated prior to attempting mating, even if they will tolerate each other at other times. Absence makes the heart grow fonder, and the sudden reappearance of a member of the opposite sex may kindle the names of desire. If the lizards show no sign of interest in each other or the female rejects the male's advances it is necessary to provide stimuli in order to make both parties co-operative. Triggering breeding behaviour takes a variety of forms. Often separating the lizards for long periods and then reintroducing them results in courtship and mating behaviour. Introducing other animals (i.e. rival males or substitute females) may trigger the indifferent partner into action. In the wild the rilllal fights referred to in Chapter 4 seem to occur mainly at the beginning of the breeding season, and may be an important stimuli for reproductive activity. Sometimes a male and female are simply not made for each other and must be found alternative partners. The order of introduction can be varied, for example a female can be introduced to an enclosure containing two or more males, an extra male can be introduced to a pair which are already acquainted, or several males can be introduced to the female's enclosure. It is of utmost importance that a close watch is kept on the lizards, and any specimens that suffer excessive violence removed immediately. Environmental stimuli will often trigger breeding behaviour in monitor lizards. A brief period of cool weather often results in mating between temperate animals when warmer conditions return. If the lizards are normally housed apart they should be introduced whilst still torpid. Many species react almost immediately to an increase in rainfall by starting intense courtship behaviour which may stop as soon as the water ceases to fall. In order to fully recreate tropical storms some imaginative herpetoculturalists have been known to provide lightening (by firing a camera nash) and even thunder (by shaking sheets of metal). Forest monitors often do not appreciate bright nashes of light; rough-necked monitors in particular appear to tind them disturbing. Several authors have reported that keeping the lights on 24 hours a day can stimulate courtship. This method should really be used as a last resort because of the considerable stress it places on the lizards. Courtship between acquainted animals often progresses very smoothly, but in many species courtship and mating are renown for th\!ir sadistic character. Generally, but not always, males 1()3
Little Book of Monitor Lizards are more aggressive than the females. and courtship can be so violent that one of the lizards dies of its injuries. To prevent this it is best to avoid introducing old. unacquainted animals that are too set in their ways to take kindly to strangers. The animals should be of as similar a size as possible or else the smaller animal provided with shelters that the larger one is unable to enter. The danger of injury can be further reduced by clipping the claws of large males prior to introducing them to females, but the use of muzzles designed to stop the male biting the female usually results in a cessation of courtship behaviour. In many species violence is restricted to a bit of back scratching and gentle "nibbling". The first sign of court~hip is usually a minute e)(amination of the female by the male, who will probe all around her body with his tongue. particularly around the vent, head and neck. It is likely that these areas contain the scent producing glands that signal the females' readiness to breed . Eventually the male climbs on top of the female, still probing furiously and often scratching at her back and neck with his foreclaws and at her tail base with his hindclaws. Eventually he forces his tail base under her and copulation is achieved. It may last only a few seconds or else it may (ontinue for several hours a day over a week or more. As soon as either party looses interest the male should be removed, partly because they are notorious eaters of eggs, but also because it is now the female's tum to become aggressive. Heavily gravid monitors have a particularly aggressive disposition. At one well-known zoo a female water monitor was digging a hole for her eggs in an outside enclosure when a large Bengal monitor happened to be passing. The two had been housed together for a long time without complications. but the water monitor attacked her neighbour with such ferocity that she literally tore it to pieces. whereupon she continued her e)(cavations Avoid touching the female unless absolutely essential but drain any large volume of water in the enclosure, because eggs laid there will be destroyed. Gravid females often like to bask at high temperatures and this should be encouraged. She must be provided with suitable nest sites. usually a nesting bolt for arboreal species or a deep tray for terrestrial species. The receptacle should eltclude light and be filled with moist, sterilised leaf litter, a moist miltture of sand and peat or damp venniculite. A depth of 30-5Ocm is usually sufficient for even the largest species. In outdoor enclosures it may even be possible to establish a colony of compatible termites to provide the perfect nest (Boylan 1995). An almost certain sign that a female is going to lay a large clutch of eggs is that she begins to fast. There is considerable danger of females becoming eggbound and a close watch should be kept on her for any signs of distress, whereupon the services of a vet are required immediately. Normally eggs are laid within 28 days of copulation, but Card (1993) suggests a pause of up to 92 days between copulation and egg1aying in V flavirufus. The female must be watched carefully and eggs removed as soon as they appear. Eggs may be laid in more than one clutch and over a period of days or weeks. After laying eggs the female should be fed as much food as she will eat, heavily laced with mineral supplements, until she regains a robust appearance. Sometimes with good feeding the female can be ready to mate again within a couple of months. Once a compatible pair has been obtained it may be possible to maximise egg output by keeping the animals on six month, rather than 12 months cycles. Temperate species should be kept warm for four or five months and fed abundant food, then the temperature lowered and feeding halted for a month. For tropical species four months of normal conditions should be followed by a small rise in ambient temperatures, higher rainfall and an increase in food for two months. Four month cycles also seems possible, but the effects of continuous egg production on the female's health must be considered.
164
Breeding Monitors in Captivity Egg Incubation As soon as the eggs are laid they should be removed from the enclosure and placed in an incubator. The eggs should be maintained in the orientation at which they were laid. Marking the top of the eggs with a pencil ensures that they are not accidentally turned. In order to turn into baby monitor lizards they need heat, oxygen and water. For many species the success of im;ubation may be detennined more by the condition of the parent animals than by precise environmental conditions surrounding the eggs. Studies have shown that eggs from properly-fed females will tolerate a remarkably wide range of temperatures and humidities, wh ich, although they affect the length of incubation and the size of the youngsters, have little or no effect upon the rate of successful hatchings(EidenmuUer I 992b, Phillips & Packard 1994). In general more humid conditions result in larger neonates and warmer conditions result in a decrease in incubation time. Most monitor lizard eggs can be incubated safely at 27-29"C with 90-100% humidity. Higher temperatures tend to give slightly less successful resull~ . It is wise to split large clutches and incubate eggs at a range of slightly different temperatures. In order to maintain humidity it is necessary to surround the eggs with water vapour. This is usually achieved by almost burying the eggs in a mixture (initiaUy around I: I by weight) of water and sterile vermiculite or perlite (available from horticultural suppliers) and enclosing the eggs and medium in a container that allows some air circulation without causing undue evaporation. This is often achieved by keeping the eggs in a sealed container and removing the top every few days to allow air circulation. In order to maintain humidity extra water may have to be added to the incubation medium from time to time. ExceUent results have also been obtained using no medium and simply keeping the eggs over water to maintain a high humidity. If the humidity is too high the eggs will sweU up with water and the pressure will destroy the embryo. Such eggs look puffy and may appear to sweat. If the humidity is too low the eggs will wrinkle and shrivel. To keep the eggs at the desired temperature they should be placed in an incubator, which can be bought or made, according to your inclination. Details of construction can be found in Broer & Horn (1985), but members of a local herpetological society will be able to provide more practical assistance. The humidity and temperature around the eggs should be monitored constantly with a thermometer and hygrometer and water added whenever the humidity begins to drop. When monitor lizards lay eggs it often comes as a surprise. Once more the advantages of being a member of the Herpetological Society are manifest If you are unprepared for the event a fellow herpetoculturalist will hopefully be happy to provide your eggs with a safe nest. Eggs that are infertile or die during development should be removed from the incubator immediately. For the first few weeks development of the eggs can be monitored by viewing them against a strong light shone tllrough a smaU hole in a dark cloth or piece of card. In fertile eggs a visible network of blood vessels appears before they finaUy turn opaque. Embryos can often be felt to move when the eggs are disturbed, but handling should be kept to a minimum. The eggs should increase substantially in weight and slightly in size as they develop and may begin to loose weight in the fmal weeks and then shrink and collapse just prior to hatching. Length of incubation shows great variation and may be determined genetically as well as being influenced by temperature . In the wild the eggs may experience great fluctuations in
165
Little Book of Monitor Lizarc1s temperature and humidity and will hatch at a time when food for the youngsters is abundant. Thus development is not necessarily continuous and may halt altogether during very cold weather, although this is not documented. Under artificial conditions the eggs should be incubated at a temperature that does not vary by more than about 2°e. Even under relatively constant temperature the eggs may hatch after an unexpectedly long or short period. The effect of temperature on the sex of hatchling monitor lizards is not fully understood (see Branch 19119 for a digestible account). Each fertilised egg cell contains genetic information on one of the chromosomes that is believed to detennine whether the hatchling will be male or female (King et al 19H2). Therefore the gender of each egg ought to be determined before it is laid. Some breeders have noted a marked difference in the sex ratios of eggs incubated a different temperatures (i.e. at lower temperatures a higher proportion of males is recorc1ed, at higher temperatures more females) but no hard data has been published.
F.gg Hatching After the monitor has developed fuUy it should poke its head out of the egg by making a slit with a sharp ridge on its snout and, after a rest of a day or so, leave the egg altogether. The eggs do not always hatch at the same time; some may even take twice as long as others, but generally they should all slit within a fortnight. Unfortunately this does not always happen with captive reared eggs, and a common problem is for the little monitor to develop fully die in the egg. The reasons for this are probably connected with the condition of the female prior to egglaying. The young of a poorly nourished female presumably lack the strength to break out of their shells. As long as the eggs look healthy they should be left alone, and only if dead eggs are found to contain fuUy developed youngsters and other eggs look poorly should any attempt be made to assist hatching. The assistance of an experienced member of the herpetological society is indispensable for this operation. Ideally, just the head of the lizard should be freed from the egg, but in practise it is very difficult to detennine the position of the head until after the egg has been opened. A small window should be made in the shell and if the lizard looks fuUy developed it can be expanded just enough to release the head. Many lizards that lack the strength to hatch unaided die within a few weeks, but some may survive. In all cases high humidity must be maintained around the hatching egg, to prevent the youngsters becoming stuck to their shells. Often the hatchling lizards still have large yolk sacs attached to their bellies which will soon shrink and drop off unaided.
Care of the Young When the youngster eventually leaves its shell it should put into a clean terrarium with a sunken, shallow water dish. Hatchling monitors without yolk sacs can often be housed together, but if any of the youngsters appear weak or are much smaUer than their siblings they should be housed separately. Very young monitor lizards have a much larger ratio of skin area to volume than adults and are much more rapidly influenced by changes in heat and humidity. If they are allowed to dehydrate or overheat at this stage they are unlikely to recover. They should be handled as little as possible. We Icnow very little about the behaviour of newly hatched monitor lizards in the wild. They are certainly very secretive animals that spend a lot of time hidden below ground or in trees and frequent shady humid microclimates. Great care must be taken to ensure that baby monitor lizards receive adequate and suitable nutrition. Newly born monitors normally refuse food for the frrst few days because they still have egg yolk in their bodies. Thereafter they need small quantities of foods at frequent lfifi
Breeding
M on i lOr~
in Captivity
intervaL,. Inv ertebrates make the best foods for young monitors. but a variety of types may have to be offered to induce the animals to stan feeding . Even young monitors ca n become obese if they are fed incorrec tly. so very small mammals (o r chopped up pieces of larger specimens) shou ld only be used as an occasiona l food. All food should be dusted with a vitamin and mineral supplement. The youngste rs grow at very different rate s and it will soon be necess
Hatchling yellow mon it or. India. (Indraneil Das)
Ili7
9
The Future for Monitor Lizards
Some monitor lizards can live happily alongside mankind, and are valued for their contribution to our well-being. These species tend to have large distributions and at least some aspects of their biology have been studied. Many other species remain poorly known, particularly those from tropical forests. It is not certain whether these lizards are really very rare, or just very difficult to find, but their natural histories are still a complete mystery. There is very little data available on the effects of commercial exploitation on monitor lizard populations, but the studies that have bee n done seem to indicate that, outside Pakistan and India, few populations have been decimated by the demand for their skins and flesh and that habitat destruction may be responsible for reductions in numbers seen in most areas. The destruction of rainforests, woodlands , sand dunes and mangroves is by far the greatest threat to the future of many monitor lizards. Yet their dilemma is mirrored in some ways by the plight of the people sharing the land: In poveny-stricken, disea se-ridden, overcrowded countries, subservient to the richer powers, the demand for food, money and space has pushed many species of animals up to, and over, the brink of extinction. So far there is no evidence that any species of monitor lizard has suffered this ultimate fate at the hand of man (although see Chapter 2), but, given their remarkable ability to evade the eyes of scientists, it is not inconceivable that some large lizard species could become extinct without ever being noticed by anyone outside their natural range. Monitor lizard s have the potential to become an important economic asset of some of the world's poorest people. Many species will live almost anywhere and eat anything. They grow very quickly and can reproduce at phenomenal rates, but not one of the hundreds of millions of lizards killed for their hides and meat has been raised in captivity. The commercial trade in monitor lizard s relies on poor people collecting the animals and selling them to exponers, who tan the hides and sell them abroad. Most of the profit, of course, is made by imponers and traders in the countries where demand for the skins is greatest; the USA, Europe and Japan. No attempt will be made to farm the animals until it becomes difficult for local people to supply enough skins to meet the demand. Thus the trade in lizard skins can be seen as yet another example of the rich nations pillaging the poorer ones, whilst at the same time preaching about the need to con serve resources for future generations. The leather industries, who slaughter millions of these magnificent creatures each year, make no attempt to farm them on a commercial basis and will doubtless continue with their piUaging until they run out of monitors, or are prevented from trading in lizard skins by international legi slation. At the same time hungry people can be expected to show nothing but contempt for laws instigated by the richest nati ons which outlaw their livelihood. The trade in reptile leather clearly provides essential income for many peopl e in the deprived parts of the world. A combination of well implemented closed season s to allow the lizards to reproduc e in peace and some attempt at commercial fanning would delay a drastic reduction in monitor populations in many areas, but only the installation of a new world order, which rejects greed and intolerance and endorses th e belief that all peopl e of the world have an equal right to health and happiness, will make the Earth a secure home for all of our children.
I (,X
Funhcr Infonnalion
APPENIllX l: PERS. OBS. - l've seen it myself. GLOSSARY PERS.COMM. - They told me. BIPEDAL - Standing on the hind legs SPINIFEX - a very tough spiny grass that BLATIlDS - roaches dominates much of the Australian landscape EPlGLOTTIS - Valve-like covering of the SVL - Snout Vent Length. A measurement glottis taken from the tip of the nose to the vent EVISCARATE - Tearing out the between the hind legs. SYMPATRIC • Sharing the same habital unappetising intestines of prey before swallowing it TEMPERATE - Away from the topics FRUGIVOROUS - fruit-eating THERMAL GRADIENT - Hot at one end, GOANNA - Australian term for a monitor cool at the other end with lots of different lizard temperatures in the middle. GULAR - Throat TL - Total Length. A measurement taken HEMIPENES - The pair of elaborate, penis- from the tip of the nose to the tip of the tail. like organs, used by males for copulation and TYPE SPECIMEN - A (usually dead) lizard otherwise kept inside the body. used in the first description of a species and HERPETOCULTURALIST - somebody considered typical of that race. who breeds reptiles or amphibians VARANIDS - Lizards belonging to the HYMENOPTERANS. Wasps etc. family Varanidae INSECTIVOROUS - Feeding on insects and VENT - The opening at the base of the tail other small invertebrates (e.g. scorpions and APPENDIX U: spiders) Jo' URTHER INFORMATION LABELLED - Made mildly radioactive
LEPIUOPfERANS - Butterflies, moths etc.
L'AL CUEASE d . be tween I'ISEFIII. SOCIETIES AND PlIBLlCATJQNS
LOR '" n • a epresslon the eye and the upper jaw Please eDclose relurD postage w beD making MELANISTIC - Black eDqwries. MESIC - Dry The Gennan group for the study of monilOr lizards MS - Unpublished manusaipt and helodenns publishes a very useful periodical. MUCRONATE· Scales bearing a small MonilOr.1haI includes English abstracts and conlains blunt spine many excellent papers. Infonnalion on subscriplions NARES - The external openings of the and back issues can be obtained from nostrils ArbeilSgemeiDscbafl Wllraoe uDd KrusteDechseD NEONATE - Newly born animal iD der DGHT. NOMINATE RACE - The subspecies with Wasgauslr. 41 the same specific and subspecific name (see 65929 FrankIun/M Chapter I). Gennany OCELLATED/OCELLATIONS - Hollow An English language publicalion. Varancws, was spots, or circles, of colour published by the Varanid Infonnalion Exchange unlil ODATRIAN • dwarf monitor-like June 1994. The edilor infonns me (Augusl 1995) thai OLFACTION - The wmbined senses of il wiU resume publication in September or OclOber. sme II and taste For infonnalion write 10 OVAGENESIS - The production of eggs VaraDix ORTHOPTERANS - Crickets. 81260 S. Sepulvada Blvd.II243 grasshoppers, locusts and the like Los Angeles CA 90045 OVIPOSITION - Laying eggs. USA PATHOGENS - Organisms and viruses that cause disease
169
Lillie Book of Moni"'r Ul.anls
'L'
As well Ihe lar~e socielies listed hclow, there arc lIlany other groups throughoul the world that ;U'C
C/o Zoologic,,1 Society of London
Regent's Park
London NW I 4RY
Ileut'chen (;esellschart rur Herpelolo(lie und
TerrarienkuDde
Postfach 1421
Locherstrasse I R
D-533~1
Reinbach
Gennany
The Herpetological Association or Africa
The Secretary
P.O. Box 20142
Durban North 4016
South Africa
The Society ror the Study or Amphibians and
Reptiles
The Treasurer
P.O. Box 626
Hayes
Kansas 67601-0626.
USA
The Asian Herpetological Research Society
Museum of Vertebrate Zoology
University of California
Berkeley CA 94720
USA
Austr.slian Affiliation or Herpetological Societies P.O. Box R307
Royal Exchange
Sydney 200n
On the 100emei the following addresses may he useful: hUp:llxtaI200,harvard.edu:8000/herpl hUp::llralcon.cc.ukans.edul-gpi.~aniissar.html
There is a uscfullist of herpetological societies (panicularly in the US) at http://www.concorde.com/-chaoslherp.vmisd orgJaq.hlrnl BIBI.IOGRAPHY English translations of papers marked # are available (or will soon be available) from The Society for the Study of Reptiles and Amphibians. Send enquiries to: R.w. Krohmer Translations Projeci Edilor Science Dept Saint Xavier University 3700 West 103rd Street Chicago 1L60655 USA References ending "ns" are cited in the lext bUI have not been seen by this author.
ABBASI ,A. & BRAUNITZER,G . 1991. Primary structure of haemoglobin from monitor lizard (Varanus rxanthrmaticus albigularis) . BioI. Chern. Hoppe-Seyler. 372:473-479. D'ABREU,E.A. 1933. J. Bombay. Nat. Hist. Soc . 36 (2):269-270. Notes on monitor lil.ards. AHL.E. 1932. Eine neue Eidechse und lwei neue Frosche von der insel Johi. Mitt.ZooI.Mus . Berlin 17(6):892-899 AKITA,K. 1992. An anatomical investigation into the muscles of the pelvic outlet in Iguanas (Iguana iguana) and Varanus (Varanus dumerifjj) with speeia!
reference to their nerve supply. Ann.Anal. 174: 119 129. AKTAN.F. !971. Guneydogu Anadoluda Varanus griseus Daud. (col Varatli). In Turkish and Gennan Auslralia
with English summary. Turk.BioI.Derg. 21 : 106-117. ALBERTS,A. 1994. Off to see the lil.ard: lessons In addition there are many colour magazines devoted from the wild. The Vivarium.~(~):26-28. 10 Ihe care of reptiles and amphibians, all of which ALI,S. 1944. J.Bomb.NaI.HisI.Soc. 44:479-480 puhlish excellent anicles on monitor lizards. They Courtship of the monitor liz.ard (Varanus monitor). indude The Vivarium and Reptile Magazine, both ANDERSON,J . 1872. Proc. Zool. Soc. London published in the US, and Reptilian, published in the 26:371-404 . On some Persian, Himalayan and other UK. The laller is my personal favourite and the only reptiles. one for which I have a current address: ANDERSON,J. 189~ . Proc.ZooI.Soc.London 63~·663. On a collection of repliles and batrachians made by The Reptilian Magazine
Col. Yerbury at Aden and its neighllourhood. ANDERSON,J. 1889. Report on the mammals, 22 Firs Close
Hazelmere
reptiles an batrachians, chiefly from the Mergui High Wycmnhe
Archipelago, collected for the trustees of the Indian Bucks HP I ~ 7TF
Museum. J.LiM.Soc.ZooJ. 21 :331-350. Greal Briwin
ANDERSON,J. 1898. Zoology of Egypt I. Reptiles and Batrachia.Bemard Quariu:h, London. ANDERSON.C. 1931. Reconstruction of the head of Mflagallia prism. Aus.Mus.Mag. 4: 147-148.
170
Funhcr Infonnalion ANDERSON,S.C. 1963. Amphibians and repliles Terrilory Field Trip Repon: ViclOria River and
from Imn. Proc. Cali. Acad. Sci.3I(16):417-498. Malardllka an:as 17-19 Oclober 1980.
ANDERSON,S.C. & LEVlTON,A.E. 1969 Repliles ARNOLD,B.N. 1984. Joumal of Zoology (London).
and Amphibians of AfghaniSlan, Proc Calif.Acad.Sci. 204: 329-354. Ecology of lowland lizards in !he
37(2):25-56. easlern United Arab Emirales.
ANDRES,A . 1904. Inlelligenz eine wUSlellwarens ARNOLD 1986. Fauna Saudi Arabia 8: 385-435. A
(Vurunus griseus). BI. Aqua. Terrar. KWlde, 15:269. key and annolllled checklisllO!he lizards and
ANDREWS,H .V. 1995. Sexual maruration in Varanus amphisbaenians of Arabia.
su/Yuwr (LAURENTI1768) wi!h notes on grow!h and ATAEV.C,A. 1987. Comparative aspeclS of !he river
reproductive effon. HerpelOlogical JoumalS (1): 189- valleys of die Swnbar and die Chandyr. Izv.
194. ' Akad.NIwk. 1'urkmcn SSR Set. BioI. Nauk. 6: 49-54.
ANDREWS,H. & GAVLKE.M. 1990. Observations 0 (in Russian).
ATIWELL,R.I,o. 1966. Possible bird-erocodile
!he reproduclive biology and grow!h of !he wa!er monilor (Vurullus sa/YalOr) aI!he Madras Crocodile CO/lIJIIeIIIIIi in Zambia. OsIrich 37:54-55.
Bank. Hamadryad 15(1):1-5. AUERBACH,R.D. 1985. The reptiles of Gaborone.
AN NANDALE.N . 1921. The repliles and balrachia of BoIswana Book Cenlre. Gaborone,
AUERBACH,R.D. 1995. Segwagwanyana. Ein
Barkuda Island. Rec.lnd.Mus. 22(4). ANON. 1909. A bird enemy -!he goanna. Emu beilrage zur afrikanischer ElhnoiIerpelOlogie. Edilion
1:1 :157-158. Chimera bei Bucher Krelh, Frankfurt Main.
ANON? 1937. A Guide 10 lhe Verlebrale Fauna of !he AUFFENBERG.W. 1970. A day wi!h nwnber 19 - A
Easlem Capt: Province Sou!h Africa. PI. 2 Reptiles. repon on a Sludy of die Kornodo monilOr. Animal mnphibians and freshwaler fIShes. AJbany Musewn, Kingdom. 73: 18-23 GmhamslOwn.
AVFFENBERG.W. 1972. Komododragons. NaI.HisL ANON. 1963. Aus befreundeten Zoos: (Varanus
81 (4): 52-59. xixun/eus in SlUugart Wilhelma Zoo). Freunde
AUFFENBERG.W. 1976. Firsl descriplion of an adull Kolner Zoo 6 (7):122.
Varanus grayi. Copeia(3):586-588). ANON. 1'165. Neues ausder Wilhelma: Gebun von AUFFENBERG.W. 1978a Grays monilor IizardVurunus mertellsi. Aquar.Tmar. 16 (9):306-307.
SlaIUS survey. World Wildlife Yearbook 1977 ANON .1961:1 New ScientiSi 40:352. Komodo dragons 1978: 129-131. AVFFENBERG,W. 1978b. In GREENBERG & breed in captivilY.
ANON . 1'178. Inuoducing !he lrulas. Hamadryad
MACLEAN (&Is.) Behaviour and Neurology of 3(1):1:1-'1.
Lizards: 301-331. GovL Printing Office. Washinglon ANON. 1'1110. Im.Zoo News. 27(5/6):51-52. Timor DC. U.S.A. Social and feeding behaviour in Varanus komoaoensis. . monilor Iitard birlh may be !he flrSl for lhe U.S.A.
ANON. 1981. Caplive breeding of !he Malayan wa!er AUFFENBERG,W. 1979a. A monilOr lizard in !he monilor (Vurunus sa/YUlOr) al San AnlOnio Zoo.
Philippines. Ornyx 15 (1):39-46. AVFFENBERG.W. 1979b. InlaSexuai differences in AAZPA BEAN Award applicalion.
ANON . 1'I1:I3a..A record size wa!er monilOr lizard behaviour of captive Varanus benga/ensis. J.Herpel. (7.5 f""llong) in Sabah, Easl Malaysia. Hamadryad 8 13(3):313-315. AUFFENBERG,W. 1979<:.. DecleCtive Auffenrerg (3) :Cover ANON . 1'I1:I3b. Tr.utic Bulletin 4 (6):71-79. gelS his beaSI. InI.WIdf. 9(2): 13-15 ImemalionaJ lr"de in skins of monilOr and legu AUFFENBERG,W. 1979d. Research on monilOr lizards 1975-1'1110 lizards. Tiger Paper 6(4):20-21. AUFFENBERG.W. 1980. The herpelOfaW\a of ANON. 1'11:14 Tempo 8(1:1): Food Trip: Dressed Komodo wi!h noleS on adjacenl areas. bayawak. (Reprinll!d in GAULKE 1984). ANON . 1'11:17. V.exulllhemmieus microS/ie/us in BuU .fla.SIale.Mus.BioI.Sci 25(2):39-156 Replilcnzoo Iguana. Repon from Replilienzoo Iguana, AVFFENBERG,W. 1981. BehaviouraJ Ecology of !he Vlissingen . Ne!herlands.#
Komodo MonilOr. Universily of florida, Gainesville. ANON . 191:11:1. AAZPA BEAN Award applicalion.
AVFFENBERG,W. 1981b Combal behaviour in Philadelphia Zoo. Breeding !he mangrove monilor Varanus bengu/ensis. J.Bombay N.H.S. 78(1):54-72. AUFFENBERG,W . 1982.Calch a lizard, use a lizard. VWUIIUS illdicus . ARCHER ,M. & WADE.M. 1976. RcsullS oflhe Ray InI.Wldf.12(6):16-19. M. Lenley Expedilion PI. I. The Allingham
AVFFENBERG.W. 1983a. The burrows of Vuranus benga/ensis. Rec.ZooI.Surv.lndia 80:375-385. Fonnation ;Uld a new Pliocene vertebrdle from
nurthern Queenland. Melll . Queensland Mus. 17 (3): AUFFENBERG,W. 1983b. Counship behaviour in '\71)-1'J7.
VaranlU bellga/ensis. In Advances in HerpelOlogy and ARMSTRONG.G. 1'11:1 I. Sou!h Auslr.dian Hcrp.
Evolutionary Biology: Essays in Honor of Ernesl E. Gruup Newslener 1'11:1 I (March):3-4. Nonhern
Williams (Rhodin & Myala eds.): 535-551. 171
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BARKER.D.G. 19M. Maintenance and repn>dllcli"n
AUFFENBERG .W . I'JK1c. Notes on feeding
hchaviour of Vumllu" hellxu/ell"i.\. J. Bombay N.H.S. of Varunus prasilllls kn,densis .11 the Dalla.< Zoo.
Proc. Replile Brecuing Symposium. Columhus:91·92 .
KII (2): 2K6·1112 .
AUFFENBERG.W. 19R(,. The Indian monilor 1i7Nd. BARNElT.B. 1979. Incuhation of Varalllls Rou/dii
eggs. Herpelofauna 11(1):21·22.
S:Ulcluary Asia. (, (4):127·111 .
AUFFENBERG.W. I'IKK. Gmy's Monilor Lizard .
BARNElT.B. 19R I. Ohservations on fish feeding
University of Florida. Gainesville.
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AUFFENBERG.W. 1989. Exploilation of monitor
BARRElI.C.I928. Li7.ards in Australian wilds.
li/ClTUS in Pakislan. Unpuhlished consultancy report 10 Bull .New York ZooI.Soc. 11(4):
BARRElT.C. 1950. Repliles of Australia. CoL<SCI.
CITES .
Melbourne.
AUFFENBERG.W . 1989h. Utili7.aJion of monilor
li/~lTds in Pakistan. Tmffic Bull. 11(1):R·12.
BARmOLOMEW.G.A. & TUCKER.V .A. 1%4.
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Size. body lemperalure.thermal conducuUlcc. oxygen
consumplion and hearlrale in Auslrali:Ul V:lTanid
UniversilY Of Florida Press.
AUFFENBERG.W. ARAIN.Q.N. & KURSHID,N . 1i7.11Tds. Physiol.ZooI. 37 (4): 341·154.
1'1'1 I. Mertcnsiella 2: 7 ·2R. Preferred habital. home BARTLElT.R.D. 19KI. NOles on caPlive
r.lII~e and movemenl pallerns of Varanus bengalensis reproduction of Varanus storri. Bull. Chicago Herp. Soc. 16 (3):65-66.
in SlIulhern Pakisl:Ul. AUFFENBERG.W. & AUFFENBERG.T. 1990. The BARTLElI.R.D. I 982.lnilial observations on Ihe
captive reproduction of Varanus storri. HerpelOfauna
replile lick AponomnuJ gervaisi as a parasile of 13(2):6-7
nlllllilOr lizards in Pakislan and India. Bull. Florida BATES,M.F. 1990. Varanus albigulariS. Rock
Mus. Nat. Hisi. BioI. Sci. 35(1)1-34. AUFFENBERG.W . & IPE.l.M . 1983. The food and Monilor. Hibernation . J.Herpel. Ass. Africa37:50
BAUER.P. 1972. Check 10 check . IntWldf. 2(1):54.
feeding of juvenile Bengal monitors (Varanus BAVERSTOCK.P.R .. KING,D., KING.M ..
h'·IIRO/,"si,,). J.Bomh.N.H.S. 80:119-124. BIRRELU .• KRIEG,M. 1993. The evolulion of the
AUFFENBERG.W .. REHMAN.H.• IFFAT of. & PERVEEN .Z. IlJR9. A sludy of Vuranusflavcscens. species oflhe Varanidae: microcmnplemenl fixalion
analysis of serum alhumens. Aus.J. Zoology
J.Bomhay. Nal.Hisl.Soc. 86 (3): 286-307. 41(6):621-638.
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des Sleppenwaraans (Varunus examhc11Ultiru.r)
Kris"I1.1 k,,"ict'wvi. lBmnhay. NaI .HisI.Soc. 87 (I); 2h·1h. Salamandra 30 (2): 109-118.
BAHL.K.N . 1917. Rec. Indian Mus. 39: 133-174. BAYLESS,M.K. & HUFFAKER.R. 1992.
Skull of Vu,.unus monitor. Observalions of egg deposilion and hatching oflhe
BAHNOTAR.R.K. & SRIVASTAVA.Y.N. 1985. svannah monilor (Vurunus exanthematirus) in
hnpaci ofrepliles on food rroduclion and c.~ptivily. Varanews 3(1):5·6.
environment All India Sd. Wrilers. Soc. Res. PubL BAYLESS.M.K. & REYNOLDS.T. 1992. Breeding
nIl 2: 116·220.265-266 . of the savarmab monilor lizard in captivilY (Varanus
BAILON,S. 1992. Esc:unosos fosiles de facimiento de exanthematicus). SouthWest. Herp.Soc. 22(1): 12-14.
Mnreda (Plio,;en medin/superior. Gr.tnada. Espana. BECKER,H.O.. BOHME.W. PERRY,S .F. 1989. Die
Revisla. espanola de Palconlologia. Numero Lungen morphologic del' Warane und ihre syslCtnatis eXlraordimlTio 1992: 11-15. che slammersgeschichichlliche. Bonn. ZooL Beitr. 40
BALSAI.M. 1992. The general care and maintenance (1):27-56. of s;,vannah monilors and olher popular monilor BECKER.H.O. 1991. The lung morphology of sl'cdc.~ . Advanced Vivarium Systems, Lakeside. Varunus yemenensis BOHME el aI 1989, and il~ C'alii',>rnia. be:uing on the Syslemalics of Afro-Asian monitor BANERJEE.V. & BANERJEE.M. 1969. Seasonal Radialion. Mertensiella 2:29-37. BEEHLER,B.M. CRILL,W. JEFFERIES.B. & v'lTialion of erthrocyle number and haemoglobin con lent in a common Indian lizard Varanus mollitor lEFFEREIES,M. New Guinc.~ h;trpy eagle all em pIS 10 Ihcngalensisl. Z"ol .Anz. IR2: 203-207. caplure a monilOr lizard. Emu 92(4):24(,·247. BARBOUR .T. 1921. Aquatic skinks and aroore<,1 BEHRMANN,H.J. 1981.Hallung und Nachzuchl von mnnilors. Copeia 1921 (I): 42·44. Varanus I. limorensis . Sal:unandra 17(3-4): 198·201. BARBOUR.T. 1943 Defence posture of Vumnus BELCHER,D. 1980. Breeding of Varanus timnrensis X"uldii. Copeia 1941( I ):56. limorensis al the Rio Gmnde Zoo. Unpuhlished Zoo BARBOUR.T. & LOVERIDGE.A. Report 1'12K.HerpclOfauna of Ulugoru and Osarnhara BELLAIRS .A. 1949. Observalions on Ihe snOUI of Mounlains. Tanganyika. Bull.Mus.Comp.Zool. Vol L. Varanus and a comp:uison wilh Ihal of olher liz'lTd, and snakes. J.AnaI.K3: 116-146. no.2: K7-265.
172
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BELLAIRS.A. & MILES,A .E.W. 1970. Apparent failure of tooth replacement in monitor lizards. BriL 1. Herp. I: IIl9·194. BELS, V.L., GASC,J.P., GOOSSE, V. RENOUS,S. &. VERNET.R. 1995. Functional analysis of the throal display in the sand goanna Varanus griseus. 1. Zool. Lond. 235:95-1 16. BENNE'IT,A.F. 1972. The effect of activity on oxygen consumption, oxygen debt and heart nue in the liUU'ds Varanus gouldii and Sauromalus llispidus. J. Comp. Physiol. 79:259-280. BENNETT,A.F. 1973a. Blood physiology and oxygen lr.ll\Spon during activity in two lizards. Compo Biochem. Physiol. 46A:673-690. BENNETT,A.F. 1973b. Ventilation in two species of lizards during rest and activity . Comp. Biochem. Physiol. 46A:653-671. BENNE'IT,D. 1992a Reptiles of the Kara Kum . Pan 2: The Caspian Monitor. Aquarist and Pondk.ecper 56 (II ):90-92 . BENNETT.D. I992b. A note 011 the burrows of
Varanus griseus caspius arowtd Repetek ,
Turlunenistan. Journal of the Southwestern
Herpetological Society (UK) 2 (1 ): 18-21.
BENNETT.D. 1992c. A noll: 011 Varanuspanoples
rubidJJs (STORR 1980) in Wanjarri. Western
AuslrJiia. Bull . Brit. Herp. Soc. 39:28-30.
BENNETT,o. I 992d. Bose's monitor lizard.
Reptilian I. (2):25-27.
BENNETT.D. 1993a. A noll: on a newly hatched
Varanus Irislis IriSlis in the Great Vic toria Desen,
Western Ausualia. BuU. Brit. Herp. Soc. 44:35-37.
BENNETT.D. 1993b. A review of some literature
concerning the rough-necked monitor lizard Varanus
rudicollis. Reptilian I (9):7-10.
BENNETT,D. 1994a. Observations on the sociaJ intemctions of Varanus (Oda/ria) slOrr; in captivily. Suuthwcsll:rn Herpetological Society Journal (UK) 2(3):2-5. BENNETT.D. I 994b. Some remarks on longevity in monitor lizards. Southwestern Herpetological Society Joumal (UK) 2(3):27-29. BENNETT.D. 1995a. Dumeril's monitor lizard (Varallus dumeri/ii). Replilian 3 (3):35-37. BENNETT.D. 1995b. The water monitor. Varanus salvalOr. Reptilian 3 (8): 15-21. BENNETT.D. In Press. Some reptiles of the Great Vktoria Descn Pan lll; The Goannas. Aquarist &. Pllndkceper 1995/6. BENNETT,D. In press b. Notes on fordging behaviour uf the water monitor Varanus sa/valOr at Kuala Sclangllr Nature Park. Selangor. Malaysia. Southwcstern Herpetological Society Jouma/ (UK). BENNETT.D. & AKONNOR.W.O . 1995. A preliminary investigruion inlo the ecology of the monitor lizard Varanus exanthemalicus in the coastal s;lvannah of Ghana. Unpubli:>hed repon to the
Deparunent of Game and Wildlife, Accra, Ghana. March 1995. 17pp. BENNETT,D. &. AKONNOR,W.O. ms. The ecology and exploitation of monitor lizards in the coasIal savannah of Ghana. BENNETT,o. &. LIM,B,L. In press. A I'\OIe on the distribution of Varanus rudicollis and Varanus dumerUjj in Peninsular Malaysia. Malay.NatJ. BENNETI',o. &. SHIMANSKA Y A,M. 1991. A revicw of IiOIIIC Sovielliteralure concerning the grey monitor VarQIIIU "ileus caspius (ElCHW ALD).
Varancws 1(8):5-&.
BERANBK,S. HIli!!. VarQllus ~ngalensis (in
CzeckoslovakWt). Art.Ter. 28(4):28.
BERG.A. 19\3. Utilila' Buunwaran (Varanus varius).
Blat. Aquar.Tcrrar. Kunde 24:717-719.
BERNEY.PL. 1936. Gould', monitor. Queensland
Nat. 10(1)
BHANOTAR,R.K. &. SRJVASTAVA,Y.N. 1985. Impact of reptiles 011 food production and
environmenL AU lnd_Sci.WriterS. Soc. (AJSWS)
Res.Publ. 1985 (2): 116-120.
BHARAT AN,E. 197I.Monitor preying on a cobra.
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Lillk Book of MOllilOr Lil.,uds
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197
APPENDIX IV:
Climatic Data
These charts show the average temperatures and levels of rainfall recorded at meteorologi ca l stati ons in areas inhabited by monitor lizards. They do not show the temperatures experienced by the li7.ards, who carefully select cooler or wanner minoclimates according to their inclinati on. Climate at Cebu, Phlllpptnes 2 50
R
30
I ,I I I I III 11I 1I' I,1~t f 25
200
20
I
150
m
15
m
] 1 III
~
M
IIIl!II!
A
M
A
I1iilI
AeOlian
... Temperature
S
a
N
0
• •
•
Climate at Muda, Solomon Islands 450[ 400 R
III • • • • =
1
.-1---.
350 300
~
p
r
25
20
250
III
IS
200 150
m J
10
( C
100
I
50
M
A
M
fl!I RaJ....n
A
5
.... Temperature
2
IYR
0
N
0
I'N
Little Book of Monitor Li7.ards
Cllmllte lit OUllrgta, Algeria 35 R
n I
6' 1
~
~
~
8[ =
2, _
=
~
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rw ,f' ~p,t
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~ l30
--
15
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0
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Wff~ O
N
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TemperahJre
(,
Climate at Durban, South Africa 140 R
25
T e
120 20
m
p
100 80
15
r a
10
u
I
60 40 m m
5
20 F
M
A
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M
~ Ralnls.
5
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... TempemlUl8
7 Climate at Edea, Cameroon 450 R
a
400
I
3 50
30 25
300
a
250
I I
200 150
m m
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I""""
~ F
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, ~
~
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... Tempera1Ure
K
200
fiJf@l 0
~ N
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m P
15
a
10
t u
~Io 0
T e
Climatic Data
Climate at Mombassa. Kenya 300
30
25 0
25
T e m
200
20
p
150
15
R
a
e a
a
I I
10
t
u 0
I!?fii
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Rain lei
Tempera1Ure
<J
Climate a\ Rlyan, Yemen R a
II : ~ ; '=bl~
12 10
a
F
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M
Rainfall
J
J
A
---
S
0
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e m p
e
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Te"l>erature
10
~o
R
Climate at Juba, southern Sudan 30 T
140 120 100 80 60 40 20 0
L
25
e m p
15 10
e a t
u
o I!?fii
Rainfall
___
II
201
Temperature
Little Book of Monitor Lizards
Climate at Cha,dzDO , Tu,km..,lstan
R
30
30
25
25
20
20
IS
15
10
I
c I
&0,,_ M
M
A
1m!!
A
Rainfall
.....
S
N
0
0
Temperatu ...
12
Climate at Karachi, Pakistan
fOOl: ; 11 : - : : : : F
J
Ii; ===~: ~
["
M ~
AM
J
AS
J
0
N
D
-e- Temperature
Rainfall
1:\
Olrmte at SrIIlBlQBI, BEIlgIadesh
~ q!:=:;,ili,j;,;:: I~ : J
F M
~
A
M
J
Rcinfall
A
J
SON
0
--- Tefll)9fature
14
Climate at Hambantota, Sri Lanka
200[ .
~ 100li
°
J
: ; i L; : :,; F
M
A
~
Rainfall
M
J
J
-e-
15
202
A
II
SON
Temperature
~ [40 BJ20 D
0
!
Climatic Data
Climate 8t Mergul, Myanmar 900
30
800
25
T
20
P
R 700
600 500
15 I 4 00
300
10 (
200
C )
100
I
M
I I I I I I I A
WI
M
A
Raln1al1
...... Temperah.re
S
0
III N
=a D
I:
1o
1
Climate at Chang Mal, Thailand 250
30
200
25
n
I IS O
20
R I
r
a
10
1 u r
50 0
e
15 100
m
m
T e m p
e F
M
A
A
M
l!J6j Rantal
S
0
N
D
0
-.- TOO'4lerature
17
I
Climate at Padang, Sumatra 30
600
R a 500 1 e n I
a I I
m m
r--- b
T e
m p
400
20
300
15
a
200
10
u
r t
100
o
~ tm'.0J
F
M
WffV;1
A
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WffM
WHMt
fW"4I!
V4?ZI
MAS Rainlall
-.
IX
203
Temperature
WffAf
0
107/41
N
D
o
Litlle Book of Monitor Lizards
-l ---------- l
Climate at BanJermasln, south Borneo 400
R a i
30
~-
350 300
• •
25 0 a I I
25 20
200 15
150
'O
100
5
50 F
A
M
s
M
mll!
Rain tal
....
o
'
J ~I
~I r
=-~iW N DA-I °.
Tempora1ure
1<)
Climate at UJUmg Padang, Sulawesi
~ ~::fi i i.:: ~ ~ ~ ~ ~.~j} ~
J
F
M
A
~
M
J
J
-e--
Rainfall
A
SON
D
Temperature
21 1
Climate at Dill, Timor
R
::~m i i ; : :.: :JJ:: ~
J
FMAMJ ~
JASON ....
Rainfall
0
Temperature
21 Climate at Darwin, NT
l;~l[ i i i :=" "=::~[l~ l
J
F
M
A
~
M
Rainfall
J
J
---
204
A
SO
Temperature
N
0
Climatil: Data
Climate at Coen, Mctlwrath Range
-------------
300
R a 200
a I I
100
0
M
L
A ~
M
s
A
o
o
N
30
[25 T• m 20
16
p e
10
a
5
u
r t
0
-*- Temporalur.
Ranlal
23
I
Cllmata at Townsvllla, Queensland
R
300
30
250
25
200
20
150
15
100
,0
m
(
c
50
)
0
o
ril'flI
Rain"!
..... Temperature
24
" ;:!II I I.
Climate at Rawlinson Range
R
40
J
F
M
~
A
r I I ;: ~ T
I II M
Rainfall
BUI II .. J ___
25
205
A
SON
Temperature
0
20(i
APPENDIX IV: METRIC CONVERSION TABLES
CM/M - INCHES/FEET
(;RAMMES/KILOS OUNCESIPOUNIJS
1em 0.39" Scm 1.96" 3 .93" 10em 1Sem S.91" 20em 7 .B7" 9 .B4" 2Sem 11 .B" 30em SOem l' 7 .7" 1'11 .3" 60em 2' 7.S " BOem 100em=1m 3' 3 .4" 4' 3 .2" 1.3m 1.Sm 4' 11 .1" 2m 6' 6 .7" B' 2.4" 2.5m 3m 9' 10.1" 4m 13' 1.S" 14' 9 .2" 4 .Sm
0.1Boz 0.3Soz 0.S30z O.BBoz 1.760z 2.650z 3.S30z 100~ S.290z 1S0~ 7.0Soz 200g 400g 14 .120z SOOg 11b,1 .60z 11b, 10.Soz 7S0g 1kg=1000g 21b , 3 .40z 1.5kg 31b,4.90z 41b , 6 .60z 2kg 4kg Blb,13 .10z Skg 11lb,O.4oz 221b O.Boz 10kg 1Skg 33.lb,1.10z 30kg 6Blbs, 2 .20 5S11b. 250kg 7000kg 15,4321b
I KM = 0,625 MILES 11»2 = 10 square feet
SQ 10Q 1Sg 2Sg SOQ 7SQ
IKM2 = 1,000,OOOM 2 = O,39MIU:S 2
207
0C _ of 100C 1SoC 200C 250C 260C 270C 2BoC 290C 300C 310C 320C 330C 340C 3SoC 360C 370C 3BoC 390C 400C 420C 440C 460C 4BoC 500C
500F 590F 680F 770F 7B.BoF BO.60F B2.40F B4.20F B60F 87 .BoF B9.60F 91,4oF 93.20F 9SoF 96.BoF 9B.60F 100.4oF 102.20F 1040F 107.60F 111 .20F 114.BoF 11B.4oF 1220F
APPENIHX V: Constructiun of a Simple Chipboard Enclosure. Chipboard (particleboard) vivariums can be made with either a sliding glass front or a hinged lid. Generally a sliding front is preferred because it allows easier access to the enclosure, and facilitates c1e;ming. 11le tools and materials needed for an enclosure giving about 3m 2 of floor area (i.e.2.5x 1.2x 1.2m (X x 4 x 4 feet) are as follows . Three sheets uf 2.5cm (I" )thick laminated chipboard 250 X 120cm (96 x 48"). Two sheets of 2.5cm (I") thick laminated chipboard 250 x 125cm (48 x 24" J. One sheet of 2.5cm (I") thick laminated chipboard 250 x 30cm (94 x 12"). Three 8 X 8cm (:Ix3") thick planks, each 500cm (192"). Two pieces of strung winduw glass at least 12mm thick 90 x 135cm (36 x 52"). 750cm (24 feet) ur double glass runners.2 air vents.Clear silicone rubber (without fungicide).Chipboard screws.Jigsaw.Saw.Screwdriver.Tape measure. The first job is to make three frames to fit inside the finished box, in order to prevent the enclosure from sagging in the middle and make it strong enough to support additional weight on top. These frames must fit exactly. so care must be taken in their preparation. For the size of enclosure outlined they will be 4R inches high and 47 inches wide, so the planks should be trimmed to make six pieces 45" long, and six more 47 inches long. They are best screwed together with simple joints (fig I) and supports added for maximum strength. If in doubt get a carpenter. The completed frames should be treated with a non toxic polyurethane varnish. Now the difficult job is done, holes must be cut into the side pieces and the ventilators fixed to the insides. This is best done with a jigsaw. Then take one of the 8 x 4 sheets, drill holes .5" from the edge at each corner and every 12" along the sides and screw the wooden frames to it as illustrated (fig 2), making sure that there is exactly I" of space left for the other pieces which will form the walls. of the vivarium. Take another R x 4 sheet and drill it in the same way as the base but leaving one long edge intact and screw it to the base. Then drill both 4 x 4 sheets 1" , 6" and II" from the bottom and screw them to the base and back . Fix the 94" x 12" sheet inside the bottom edge of the base through the holes drilled in the sides and screw the chipboard to the frames at 12" intervals. Place the remaining sheet on top of the box (don 't fix it yet). glue the glass runners all round the front edge of the box and leave them to cure for 24 hours. Then simply slot in the gla~s and get someone to hold it in place while you screw the top to the back and sides. Screw the frame to the top and "job's a good 'un! " Enclosures to house water monitors and those requiring high humidity and/or rainfall must be made waterproof. The easiest way of doing this is to coat the entire inside surface with a plastic solution made for treating concrete pools (these can normally be used on chipboard without special preparation, but check with the manufacturer if in doubt). Once dry, this provides a tough yet flexible protection against water damage which should last for many years.
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VgiLIeni (B. Eiden muller)
V.eremius, S.Edagee (Gasca -yne) WA (R.Browne-Cooper)
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Vstorri
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Vacanthurus (B.EidenmulJer)
Vbaritji (J.Wombey)
V.timorensis hatchling (B.Eidenmuller)
V. timorensis
V.simi/is hatchling (B.Eidenmuller)
V.storri (B.Eidenmuller)
Varanus bengalensis nebulosus, Thailand (A.Mahommet)
ERRATA Please note
following amendments:
COVER PICTURE: V.olivaceus by S.DILKS PAGE 1 PICTITRE: V.salvadorii by T.GARNER PAGE 122: Picture by PAGE 139: "Opposite" read "Overleaf' PAGE 169: should read: • wet IN COLOUR VERSION ONLY: COLOUR PLATE 4: by C.TRAEHOLT Bottom picture by S.GROVES COLOUR 15: Bottom right picture by E.R. PIANKA
