Friday, October 10, 2014

Desert monitor (Varanus griseus) -- Under Threat




Uzbekistan (Stamp 1993) Varanus griseus - Desert monitor - Uzbekistan This beautiful large lizard Desert Monitor (Varanus griseus) can reach lengths of
1.6 m .

KingdomAnimalia
PhylumChordata
ClassReptilia
OrderSquamata
FamilyVaranidae
GenusVaranus



Description

The desert monitor is the most northerly distributed monitor species and one of the largest reptiles in its expansive range Its body is long and robust, with sturdy limbs, and a long, powerful tail which can be used liked a whip in defence. The nostrils of this species are particularly distinctive, comprising diagonal slits much closer to the eye than the tip of the snout.

Colouration is highly variable, but is always far more vivid in juveniles, which are generally yellow or orange with bold black bands running across the body and tail. As the desert monitor ages its colour and markings fade, becoming light brown, yellow or dark grey, with faint or non-existent banding. In some adults the upperside may be marked with creamy spots and mottling  or with small, dark spots extending to the tail and throat. This species is divided into three subspecies which occupy distinct geographical regions and can be identified by size, tail shape, and the number of bands on the body and tail.


Biology

Active during the day, the desert monitor emerges from its burrow in the early morning, and basks in the sun at the entrance in order to raise its body temperature. When sufficiently warmed, it begins to forage, using its long forked tongue to detect chemical cues in the air that help it to track down prey. Once its quarry has been sighted, the desert monitor either rushes at it directly, or stalks it to within a few metres, before sprinting forwards. Prey is dispatched by biting the neck, which disrupts breathing, and also by violently shaking the animal in its jaws, after which it is swallowed whole. Desert monitors are opportunistic predators, and employ an impressive range of skills in the pursuit of food, including tree-climbing, swimming and digging. Their diet includes small mammals, birds, eggs and insects, and they will even tackle challenging prey such as hedgehogs, tortoises and venomous snakes.

During a single day, desert monitors range over large distances, usually between five and six kilometres, returning to their burrow before sunset. Although the desert monitor is a solitary species, individuals may occur in relatively high densities over a small area, which is described as a “settlement”. Within settlements, the individuals tolerate each other’s presence, although ritualised combat may occur to assert dominance. Desert monitor mating occurs over a 15 to 20 day period during the first two-thirds of June. Males typically locate a mate by following tracks in the sand, but while tracking may occur over days, and can range over many kilometres, it is frequently unsuccessful. If the male does catch up with the female, he may follow her closely for some time before copulation occurs.

Egg-laying generally occurs from late June to early July, and is preceded by the female digging a burrow with two shafts, one leading to a chamber which the female inhabits, and the other to a chamber in which a clutch of between 10 and 20 eggs is laid. After depositing the clutch, the female tightly packs the shaft leading to the eggs with sand, and then remains in the vicinity of the burrow to defend it from other desert monitors. In early October, after an incubation period of around 110 days, the eggs hatch, but the young do not yet attempt to dig to the surface. Like adult desert monitors, they hibernate through the winter, emerging from the subterranean chamber in the following spring.

Threats

The species is listed in the Red Book of the IUCN and the CIS, and also in Appendix I of the CITES Convention on International Trade in endangered species of flora and fauna. The main causes of reduction in the species has been the loss and fragmentation of its habitat as a result of the widespread conversion of steppe to agriculture, which in some areas has caused the desert monitor to become rare or even extinct. Other threats are hunting for its skin and its use in the traditional medicinal trade.
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