That Reptile Blog – Reptile, Amphibian and Exotic Pet Care and Information

I remain awed by the learning abilities and complex behaviors evidenced by the Water and Lace Monitors I cared for at various zoos…spend time with any species and you’ll quickly see why.  Despite being popular study subjects, monitors are constantly surprising us.  For example, the current issue of The Journal of Herpetology (V44, N3, Sept 2010) documents an entirely new behavior for any monitor species – cooperative nest building and nest guarding in Rosenberg’s Monitor (Varanus rosenbergi).

Nest Defense by both Sexes

A 16-year-long study of this species on Australia’s Kangaroo Island has revealed that females guard their nest sites for up to 3 weeks after egg deposition, a behavior that has not been documented for any other monitor (3 species, including the Komodo Dragon, may return to the nest site on occasion, but seem not to remain nearby).  Amazingly, in 8 instances a male joined the female in protecting the eggs. Read More »

Herpetologists still reeling from the recent (April, 2010) discovery of the 6-foot-long Northern Sierra Madre Forest Monitor (Varanus bitatawa) in the Philippines have had yet another shock this week – a large, Red-Headed Monitor Lizard, previously unknown to science, has surfaced in Indonesia!  A glossy black body and brilliant red head led to its being christened the Torch Monitor.  Also known as the Sago Monitor (Varanus obor), it is the only Varanid that sports red coloration. Read More »

It’s well-known that the world still hides countless “undiscovered” animals and plants – even Central Park in NYC recently yielded a previously unknown centipede.  However, it is still something of a surprise when large, colorful creatures remain unseen into modern times.  Such is the case for the Northern Sierra Madre Forest Monitor (Varanus bitatawa), a spectacularly colored, 6-foot-long lizard that has been designated as a new species in the current (April, 2010) issue of the journal Biology Letters. Read More »

Despite – or perhaps because of – its immense size, impressive armament of teeth and scarcity, the spectacular Crocodile Monitor Lizard (Varanus salvadorii) is often considered the crown jewel of private and public monitor collections.

I became acquainted with these formidable giants when they were first imported into the USA, and have cared for several at the Bronx and Staten Island Zoos.  Their husbandry is straightforward, but little is known about their lives in the wild.  Today I would like to summarize what we do know; please see the article referenced below for notes on captive care.

Description

Crocodile Monitors approach 9 feet in length – nearly as long as the famed Komodo Dragon, but less stoutly built.  There are recurring but unverified reports of much longer individuals.

The Crocodile Monitor’s prehensile tail often exceeds 5 feet in length.  The body is dark gray to black in color and marked with yellow spots, making for quite a spectacular appearance.  The snout area, especially in mature males, is large and bulbous.

Crocodile Monitors are unusually large for canopy dwelling lizards…the 3 foot long black tree monitor is far more typical.  However, aided by slender bodies, long claws and prehensile tails, they are very agile climbers.

Their teeth are unique among monitors, being serrated and over-lapping – possibly an adaptation for carrying large prey high above the forest floor.

Range and Habitat

Crocodile Monitors are found only in southern New Guinea.  Highly arboreal, they seem restricted to the canopies of mangrove swamps and lowland forests along rivers.

Status

Little studied due to the inaccessibility of their habitat, the Crocodile Monitor’s limited range renders it a conservation concern.  Listed on CITES Appendix II.

Reproduction

Females lay 6-12 eggs at a time, and up to 3 clutches per year in captivity (multiple clutches may be a function of food availability), with arboreal nest sites being favored.  In common with other tree-dwelling monitors, they likely deposit eggs in tree hollows and similar sites above ground in the wild.

Diet

Their natural diet has been little studied, but probably includes nearly any animal that can be overpowered.  Likely candidates would be cuscus, tree kangaroos, naked-tailed rats, bandicoots, possums, bats, birds, frogs, snakes, lizards, invertebrates and carrion.

An Undiscovered Giant in New Guinea?

Long a creature of legend, the Crocodile Monitor is the source of rumors alleging “Papuan Dragons” of 20 feet in length.  This specie’s habitat is inaccessible and barely explored….I like to believe that it or an as yet un-described monitor may indeed reach such lengths.

A Calculating Reptile

Like all Varanids, Crocodile Monitors are highly intelligent.  One huge adult that escaped its enclosure at the Bronx Zoo wedged himself behind a cage while attempting to hide from myself and a co-worker.  As we moved into position to flush him, he very deliberately peered around first one and then the other side of his hideout, trying to keep us both in sight.  When we backed off, he followed our progress, again changing position periodically to ascertain where we were.

The lizard remained stationary while we were near, and only ran when we gave him some space.  When he did move, the old fellow made unerringly for a more secure retreat that he had obviously “decided upon” while in hiding.

Further Reading

Please see my article Monitor Lizards: an Overview for information about the captive care of this and related species.

A comprehensive field report on the crocodile monitor’s habitat is posted here.

 

Crocodile Monitor image referenced from wikipedia and originally posted by Ltshears

 

Browsing the pages of Herpetologica and other journals over the years, I several times came across field studies indicating that certain populations of savannah monitors consumed diets composed entirely of invertebrates.  In certain seasons, the lizards gorged on either locusts or land snails exclusively for months on end.  When some captives fed largely upon rodents showed evidence of kidney and liver damage and intestinal impactions, articles in popular magazines began calling for insect-based diets.

Canned Diets

Savannah monitors may approach 5 feet in length, and thus an insect-based diet is difficult to arrange…thousands would be needed weekly in some cases.  Zoo Med’s Canned Tegu and Monitor Diet provides a handy solution.  Formulated with these lizards in mind, it is readily accepted by most individuals.

After reading the aforementioned articles, I took a moderate position as regarded the savannah monitors under my care in public collections, using canned food as 60-75% of the diet.  I supplemented the food of adults

once weekly with vitamin/mineral powder  and that of juveniles 3-4 times weekly.

Invertebrate and Vertebrate Food Items

The easiest way to supplement canned food without using mice is to establish a breeding colony of Madagascar hissing roaches (even the well-armored adults are readily accepted) and nightcrawlers.  Crayfish, if available to you, are a great monitor food.  Other useful food items are land snails (available in seafood markets), tomato hornworms, hard boiled eggs (in moderation, i.e. once monthly) and canned grasshoppers , silkworms  and snails.  Pink and fuzzy mice (these are preferable to adult mice and rats) may be offered every 10-14 days.

My Observations of Wild Black and White Tegus

My observations of black and white tegus in Venezuela leads me to believe that, at least in llanos habitat, these lizards consume far more large insects, turtle eggs and frogs than rodents.  Mammals are taken when available, mainly as carrion or unearthed rodent nests.

I have kept tegus for lengthy periods on rodent-based diets but now counsel more variety…I suggest feeding as described above, but with canned food comprising a smaller portion (i.e. 25-50%) of the diet, and rodents, preferably pink and fuzzy mice, being offered once weekly.  If your tegu will accept whole fish (i.e. large shiners), use these in place of mice.

An interesting article on savannah monitor natural history and diet in the wild is posted at http://www.mampam.com/index.php?option=com_content&task=view&id=36&Itemid=76