White-Throated Monitor

ORDER: Squamata

FAMILY: Varanidae

GENUS: Varanus

SPECIES: albigularis

DESCRIPTION:

All monitors have long, forked tongues, sharp teeth, relatively long necks, pointed snouts, sharp claws, and non-autonomous tails. The eyes have eyelids and round pupils. Body is usually fairly massive, with four powerful legs, each bearing five clawed toes. The tail is thick and long and functions as a rudder, as a prehensile organ and as a weapon. It is twice as long as the body. The body is covered with various small, non-overlapping scales that form a granular pattern. Typically gray-brown with conspicuous white or yellowish markings. Can grow to six feet, but average length is four feet.

GEOGRAPHICAL RANGE AND HABITAT:

South Africa north to Zimbabwe, south into Namibia, and northeast into Mozambique. It lives in dry steppe or savannah regions, seeking shelter under tree roots or in burrows during hottest part of day.

DIET:

Diurnal. Carnivorous. Generalized food preferences, ranging from reptiles, to birds, to eggs, but consisting mostly of a variety of invertebrates such as snails and insects. Carrion is also eaten. Fed twice a week in captivity.

LIFE CYCLE/SOCIAL STRUCTURE:

Hunt over a large home range of around 2.3 square miles for females and 7 square miles for males (keeping to a much smaller part of their home range during the dry season-when food and thus energy is in shorter supply). Mating and egg incubation occurs during the drier months with hatching coinciding with the onset of the rainy season. Seven or more soft smooth leathery-shelled eggs are buried in the ground. Sexual maturity is reached at three to five years. Life expectancy is about 15 years.

SPECIAL ADAPTATIONS:

Monitors swallow small prey or pieces of large prey whole rather than chew it as do iguanas and other lizards. Like snakes, they have a strong bony roof to the mouth which protects the brain from being damaged by the passage of large mouthfuls. They can also greatly increase the size of their mouth cavity by spreading the hyoid apparatus and dropping the lower jaw. Their long, deeply-slit tongue is also snakelike and is often protruded to follow olfactory “tracks". Other similarities with snakes are the shape of the vertebrae, the chamber structure of the heart, and the absence of a urinary bladder.

Powerful legs allow them to run swiftly. Long, sharp claws make them good climbers; claws also are used as tools to dig out dens or enlarge rodent dens for their own use.

When lizards walk and run, they amble from side to side, flexing their bodies laterally. The muscles that are responsible for this flexing work in a different direction to expand the chest for breathing. Thus at higher speeds flexing predominates and breathing suffers. Monitors, however. have shown no constraint on oxygen consumption because they have a throat pump. As the monitor breathes, air is drawn both into the lungs and into an expanding cavity in the throat area. The cavity contracts, pumping the air into the lungs.

INTERPRETIVE INFORMATION::

Also known as the Cape Monitor. The family of monitor lizards (31 species with 58 subspecies) includes the largest lizards now in existence; several species reach 5 feet or more. The largest is the Komodo Dragon at ten feet long, and the smallest is the eight inch short-tailed monitor of Australia. Monitors can get quite agitated if brought to bay. At first they inflate their bodies and hiss. Then they attempt to deter any attack by violently lashing the tail like a whip. Finally they may attack by grabbing their adversary with powerful jaws and clawing with their feet.

OUR ANIMALS:

1 Female.

STATUS IN THE WILD:

Varanids are especially vulnerable because of their requirements for large areas of suitable habitat. This trait, coupled with the use of their skins for the leather trade and local peoples hunting them for meat has led to the CITES classification of all monitors as threatened. These monitors are often killed out of fear by native peoples, and also parts are used in traditional medicine.

BIBLIOGRAPHY:

1. Alberts, Allison. "Lessons from the Wild", The Vivarium. Vol.5, Issue 5, pp 26-28.
2. Burton, Maurice. 1975. Encyclopedia of Reptiles. pp.188-190.
3. Fountain, Henry. “Turbocharged Lizards”. New York Times. June 8, 1999.
4. Grzimek, Bernhard, ed. 1984. Grizmek's Animal Life Encyclopedia, Vol.6.
5. Visser, Gerard. "Monitors and the Rotterdam Zoo", The Vivarium, pp.19-22.