Behavior

Monitor lizards adopt characteristic defensive postures, flattening themselves from side to side and extending their gular pouches to make themselves appear as large as possible. Often they hiss loudly and flick their tongues. Big species lash their tails like whips with considerable accuracy. Some species stand up erect on their hind legs during such displays.

Varanids appear to be much more intelligent than most lizards. At the National Zoo in Washington, D.C., individual

Komodo dragons have their own "personalities" and recognize each keeper. Recent experiments on captive V. albigularis by John Phillips at the San Diego Zoo suggest that some varanids can actually count. Lizards were conditioned by feeding them groups of four snails in separate compartments with movable partitions, opened one at a time allowing monitors to eat each of the four snails. Upon finishing the fourth snail, lizards were allowed into another chamber containing four more snails. After such conditioning, one snail was removed from some snail groups; lizards searched extensively for the missing fourth snail, even when they could see the next group. Such experiments showed that these varanids can count up to six, but with groups of snails larger than six, the monitors seemed to stop counting and merely classified them as "lots," eating them all before moving on to the next chamber. Such an ability to count probably evolved as a consequence of raiding the nests of reptiles, birds, and mammals, since average clutch or litter size of prey would usually be less than six. A pair of V. niloticus were observed to cooperate when raiding a crocodile nest in Africa. After one monitor lured a female crocodile guarding her nest away into the water, another monitor dug into the nest and began eating eggs and hatchlings. Soon it was joined by its accomplice. Similar observations have been made of monitors raiding bird nests.

Some varanids, such as Varanus niloticus and V. mertensi, are highly aquatic, leaving water only to bask nearby or to dig nest burrows and lay their eggs. Others, such as V. indicus, V. mitchelli, and the so-called water monitor, V. salvator, are more terrestrial but are strong swimmers, very much at home in the

Bengal monitor lizards (Varanus bengalensis) engaged in a ritual trial of strength. These fights take place during the mating season; the stronger lizards winning the females. Neither contestant is harmed during the struggle—as soon as one is wrestled to the ground, the battle is over. (Photo by Zingel/Eichhorn, F. L. Bruce Coleman, Inc. Reproduced by permission.)

Bengal monitor lizards (Varanus bengalensis) engaged in a ritual trial of strength. These fights take place during the mating season; the stronger lizards winning the females. Neither contestant is harmed during the struggle—as soon as one is wrestled to the ground, the battle is over. (Photo by Zingel/Eichhorn, F. L. Bruce Coleman, Inc. Reproduced by permission.)

Dragon Animal Medicine

water. Komodo dragons also swim well, which may facilitate colonization of islands. Even desert monitors swim with ease.

Using high-tech radiotelemetry, Auffenberg followed movements and body temperatures of Varanus olivaceus in the Philippines. Surprisingly, he found that this large, rare, previously unstudied, arboreal monitor feeds primarily on fruit. His similar extensive study of Varanus bengalensis, primarily in India and Pakistan, showed that this wide-ranging terrestrial monitor feeds primarily on a wide variety of arthropods (earthworms, crustaceans, snails, many other vertebrates, as well as their eggs and young, are also eaten when available).

One of the most arboreal of all monitor lizards is the beautiful green V. prasinus from New Guinea and Cape York, Australia. These small climbing monitors have strongly prehensile tails and spend most of their lives above ground in trees. Several new species have recently been described that belong in the prasinus group.

In the Australian desert, as many as six or seven species of Varanus occur together in sympatry. All are exceedingly wary, essentially unapproachable, and unobservable lizards. Fortunately, however, they leave fairly conspicuous tracks, and one may deduce quite a lot about their biology from careful study of this spoor. Each species leaves its own distinct track. The largest species, the perentie, V. giganteus, reaches 6.6 ft (2 m) or more in total length, whereas some smaller "pygmy goannas," such as the ubiquitous and very important lizard predator V. eremius, achieve total lengths of only about 15.8 in (40 cm). Two other species, V. gouldii and V. tristis, are intermediate in size. Individuals of all four of these species range over extensive areas and consume very large prey items, particularly other vertebrates (especially lizards). Daily forays typically cover distances of a kilometer or more. V. tristis and two other little-known small species, V. caudolineatus and V. gilleni, which have strongly curved very sharp claws, are semiarboreal. Four other species (V. bre-vicauda, V. eremius, V. gouldii, and V. giganteus) are terrestrial.

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