Almost all monitor lizards are active predatory species that raid vertebrate nests and eat large vertebrate prey (some
smaller species also feed extensively on invertebrates, including centipedes, large insects, earthworms, crustaceans, and snails). Many monitor lizards are top predators in the communities in which they live. Varanids are very active lizards that forage widely, using their forked tongues extensively to locate and discriminate among their prey by scent (vision and sound are also used).
When foraging, V. gouldii hunt by smell, swinging their long necks and heads from side-to-side, constantly flicking out their long forked, very snake-like, tongues, searching for scent trails and sweeping over as big an arc as possible so that they cover as much ground as possible. Upon detecting a scent signal, these monitors follow the trail to the source, usually a burrow, and dig up the intended prey. Digging is methodical, using the forearms and sharp claws of the forefeet with the pointed snout, mouth, and sharp teeth right in between ever ready to snatch up prey as they dash to escape. Sand monitors consume many geckos captured in their diurnal retreats, dead-end burrows. Many diurnal species of lizards are also eaten (Ctenophorus, Ctenotus, Lerista, Lialis, Menetia, Moloch, Pogona, as well as other Varanus, including V. brevi-cauda, V. caudolineatus, V. gilleni, and V. gouldii). They also eat reptile eggs, baby mammals, and baby birds. These lizards very probably eat any other lizard that they can catch. Among specimens examined, the largest relative prey mass was a Pog-ona minor estimated to weigh about 0.88 oz (25 g) eaten by a V. gouldii that weighed 6.3 oz (180 g), or about 13.9% of its weight.
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