Dave Taylor's African Safari: Trophic Level III: Omnivores and Small Carnivores - Monitor Lizards

Trophic Level III: Omnivores and Small Carnivores
Monitor Lizards
Page 4

There are 30 species of monitor lizards found in the world. Only three of these are found in Africa. The other species are found in southern Asia and Australia.

There is a tremendous variation in the size of monitor lizards. The world’s largest lizard, the Komodo dragon, is a member of this family. It reaches lengths of 3 meters (10 feet) and can weigh 135 kilograms (300 pounds). It is big enough to prey on deer and has been reported to eat people. Komodo dragons are only found in a few islands in southeast Asia. The smallest monitor lizard reaches a length of only 20 centimeters (8 inches) and weighs 20 grams (.7 ounces).

Two species, the Nile and the savanna monitor lizards are found in the Serengeti-Mara.

Nile Monitor Lizard
Varanus niloticus

Length: Usually 1 to 1.4 m (3 feet 4 inches to 4 feet 8 inches) but some reach 2 m (6 feet 8 inches)

Status: Common, although they are looked upon as a delicacy by some human residents.

Habitat: Nile monitors are found near rivers, lakes, marshes, streams and surrounding woodlands.

Food: All monitor lizards feed on other animals. The Nile monitor feeds on wildlife found along rivers, lakes and marshes. Food includes crocodile and turtle eggs, crabs, mussels, frogs, fish and birds. Young monitors eat smaller prey such as insects and frogs.

It takes two days to digest eggs.

Nile monitors have been seen to use their bodies to corral small fish trapped in ponds as the Grumeti River dries up. The lizard gradually forces the tiny fish into a small pocket of water where it catches them at its leisure. When loaches (a small species of fish) migrate up stream, monitors will wait for them by shallow water or small waterfalls and catch the fish while they are exposed.

Nile monitors are a major predator of crocodile nest sites if they can break into them when the female crocodile is not alert. Sometimes, they are not fast enough and wind up feeding the crocodile!

When it feeds on larger prey, it tears out morsels by using its jaws and foreclaws. It will sometimes use its forefeet to push food down its throat.

Prey is usually seen and then pursued. Once caught, the monitor grabs the prey with its jaws and shakes it in the manner in which a dog shakes its small prey. It will then beat it against a rock or other solid object. Monitors have vice-like jaws and seldom let go of their prey.

A monitor will locate dead animals by using its tongue to scent the air in the same way a snake does. Like snakes, monitors have a special organ in the roof of the mouth known as the Jacobson’s organ that detects scents and odors.

Also, like snakes, a monitor can dislocate its lower jaw by making it become unhinged. This allows it to swallow much larger prey than its mouth would seem to allow. They are the only lizards that can do this. Monitor lizards usually swallow their prey whole.

Social System/ Behavior: Nile monitor lizards are Africa’s largest lizards. Males will wrestle with other males to assert their dominance and claim a territory.

In the rainy season, females dig a hole in a living termite mound and lay 20 to 60 eggs. The termites quickly repair the damage and the eggs are left to incubate in their sealed nest. The temperature and humidity is constant inside the termite mound.

The young hatch one year later and dig themselves out. The female has nothing further to do with them and the hatchlings must find food on their own. They make their way to water and feed on insects and frogs in the weed beds.

There is little sexual dimorphism. Females are as big as males. Unless they are breeding, monitor lizards are solitary. They will come together to share a favorite basking area or to feed on especially abundant food.

During the daytime, they will lie on dense vegetation or among dry leaves along rivers and lakes. They escape into the water if danger threatens.

Predators: Crocodiles sometimes manage to capture adults. Many young also fall victim to crocodiles. Wading birds such as goliath herons and marabou storks will catch the smaller, younger lizards. Fish will also eat any young that venture too far from shore. Most young do not survive to reach adulthood. Leopards and foraging monkeys may also take the occasional lizard. Rock pythons are another predator to be avoided.

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