Australian Reptiles - Goannas

Tuesday, Dec 20, 1988 at 07:18

Member - John and Val

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One of the most widespread and commonly encountered reptiles on our travels are the goannas. While many campgrounds have their own resident population that prowl around looking for food scraps, the chance encounter with a big goanna out in the bush is a memorable occasion.

Goannas or monitor lizards belong to a group of lizards found in Africa, Asia and Australia. The group includes the Komodo Dragon, the worlds largest lizard, and the Australian Perentie, which can grow over 2m in length.

Monitor lizards belong in the genus Varanus (Family Varanidae) and in Australia are usually called goannas. There are around 20 to 30 species of monitor, about 15 of which are endemic to Australia.

They are a varied group of carnivorous reptiles that range greatly in size. Most are large reptiles although some can be as small as 20 centimetres (7.9 in) in length.

Goannas are predators and are often quite large and bulky, with sharp teeth and claws. They have long necks, powerful tails and claws, and well-developed limbs. The tongue is deeply forked like that of a snake and is constantly flicked in and out when the animal is alert. Recent studies suggest that monitor lizards (including goannas) are venomous and have oral toxin-producing glands.

Most species are terrestrial, but arboreal and semiaquatic monitors are also known.

Almost all monitor lizards are carnivorous, although some are also known to eat fruit. Goannas feed on small animals including insects, other lizards, snakes, mammals, birds and eggs. All species are also scavengers and will readily feed from the carcasses of large animals like cattle and camels, being attracted to rotting meat.

Most goannas are dark coloured, in tones of greys, blacks and greens. Desert dwelling species also feature yellow-red tones. Camouflage patterns include bands and stripes to splotches and circles.

Goannas are oviparous, laying from 5 to 35 eggs, which they often cover with soil or protect in a hollow tree stump. Most lay eggs in a nest or burrow, but some species lay their eggs inside termite mounds. This offers protection and incubation, additionally the termites may provide a meal for the young as they hatch. Unlike other species of lizards, goannas do not have the ability to regrow limbs or tails.

Goannas are found throughout Australia, except for Tasmania. Most species are ground dwelling. The Sand goanna (Varanus gouldii – also known as Gould's goanna), is the most common of all goannas. They are often found close to a burrow or den, which may be a hollow log, or if in the plains a dug burrow which can be up to a metre deep. They may even take over rabbit warrens.

Some goannas live in rocky outcrops and cliffs, often having special adaptations that aid their survival. Some terrestrial goannas may occasionally climb trees or outcrops, but there are plenty of primarily arboreal species. The lace monitor (Varanus varius) is probably the best-known amongst these. The lace monitor is the second largest of all goannas, reaching lengths of up to 2 metres.

Mertens' water monitor (Water goanna – Varanus mertensi), found in lagoons and rivers across northern Australia, is streamlined for swimming, using its tail as a paddle. Most other goannas are good swimmers, but tend not to voluntarily venture into the water.

The Goanna features prominently in Aboriginal mythology and Australian folklore. Traditionally, it formed an important part the diet of many Aboriginal peoples. Aborigines who hunt goannas for food consider the Perentie to be a high-risk but tasty prey.

Goannas are usually wary of humans and will run away, up a tree, or into water if alarmed. However some overcome that fear and if there is a possibility of getting food goannas will happily live around humans. For this reason campers should take care not to leave food out at campsites, and should secure rubbish out of goanna reach.

Goannas run swiftly and when pressed will sprint short distances on their hind legs. They may also rear up when threatened, chased or cornered. They also inflate flaps of skin around their throats and emit a harsh hissing noise. An alarmed goanna can mistake a standing human for a tree and attempt to climb off the ground to safety, creating a painful, and distressing situation for both lizard and human.

Goannas are a protected species throughout Australia.
J and V
"Not everything that can be counted counts, and not everything that counts can be counted."
- Albert Einstein
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