Rock Monitor

The rock monitor (Varanus albigularis), also known as the white-throated monitor, is a large and heavily built monitor lizard of eastern and southern Africa. Most adults are roughly 1.2–1.5 m long, although exceptional individuals can approach 2 m. Adult males commonly weigh around 6–8 kg, while females are usually lighter at about 3.2–5 kg.

The body is powerful, with a broad head, strong limbs and claws and a thick tail. Colour varies from grey and brown to olive, usually with paler spots or bands. The throat is often cream or whitish, while the deeply forked tongue is used to collect chemical information from the surroundings.

Three subspecies are currently recognised. The nominate Varanus albigularis albigularis occurs across much of southern Africa, V. a. angolensis occurs mainly in Angola and neighbouring south-central Africa, and V. a. microstictus ranges through East Africa and is widely known as the black-throated monitor.

The animals photographed on this page in South Africa belong to the nominate southern form, V. a. albigularis.

Rock monitors inhabit savanna, bushveld, open woodland, grassland and rocky country. They also occur around farms and settlements where suitable cover remains.

The species is mainly terrestrial but climbs well and uses burrows, rock crevices, hollow trees and abandoned termite mounds as refuges. Access to sheltered retreats is important for avoiding both predators and temperature extremes.

Despite their size, rock monitors do not depend mainly on large vertebrate prey. They are opportunistic generalists and often concentrate on abundant, relatively slow-moving food. South African diet studies found millipedes and tortoises to be particularly important, together with insects, snails, eggs and a variety of small vertebrates.

Much of the active day is spent walking through the landscape, investigating potential feeding sites and moving between areas where prey is abundant. The forked tongue samples chemical traces that can reveal food hidden from sight, while vision becomes important once prey is encountered.

Rock monitors can be selective in what they tackle and may favour prey that provides plenty of food for the effort needed to catch and handle it. Feeding changes with season and local prey availability and can increase strongly during the warm wet season when invertebrates are abundant.

Rock monitors are diurnal and usually solitary. Activity is strongly seasonal in many parts of southern Africa: lizards are far more active during the warm wet season, while movement can fall sharply during cooler dry months.

When threatened they may flee into a burrow or crevice, but a cornered animal can defend itself with powerful claws, jaws and sweeping blows from the tail.

An experiment published in 2008 showed that juvenile rock monitors could solve a new feeding problem on their first attempt. When tested again, they reached the food faster and spent less time on ineffective actions, showing that they could quickly adjust their behaviour through experience.

Breeding takes place during the warmer part of the year. Males may wrestle for access to females, using their powerful bodies and forelimbs in prolonged contests.

Rock monitors can produce very large clutches. Published records range from about 6 to 51 eggs, with the largest clutches produced by large females. Eggs are deposited in protected sites such as burrows and termite mounds, where relatively stable temperature and humidity provide suitable incubation conditions. Development lasts several months and the hatchlings are independent after emerging.

The rock monitor is classified as least concern on the IUCN Red List.

Local populations can nevertheless be affected by habitat loss, road mortality, persecution and collection for meat, skins or the pet trade. The species is listed in CITES Appendix II, so international commercial trade is regulated.