Desert monitor (Varanus griseus)

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Desert monitor in habitat
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Desert monitor fact file

Desert monitor description

KingdomAnimalia
PhylumChordata
ClassReptilia
OrderSquamata
FamilyVaranidae
GenusVaranus (1)

The desert monitor is the most northerly distributed monitor species and one of the largest reptiles in its expansive range (2) (3). The 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 (2). In some adults the upperside may be marked with creamy spots and mottling (3) or with small, dark spots extending to the tail and throat (2). 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. Varanus griseus griseus has a rounded tail and highest number of bands, Varanus griseus caspius reaches the largest size and has a laterally compressed tail, while Varanus griseus koniecznyi is the smallest subspecies and has the fewest bands (2).

Also known as
Agra lizard, Agra monitor, Baghdad small-grain lizard, grey monitor.
Synonyms
Psammosaurus arabicus.
Size
Length: up to 1.3 metres (2)
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Desert monitor 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 (2). 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 (2) (4). 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 (2). Desert monitors are opportunistic predators, and employ an impressive range of skills in the pursuit of food, including tree-climbing, swimming and digging (2) (3). 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 (2).

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 (2).

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 (2).

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Desert monitor range

Subspecies Varanus griseus griseus is found from the Rio de Oro in the Western Sahara, east to Egypt and northern Sudan, its range also extends throughout the Arabian Peninsula, and from there, north to south-eastern Turkey. Subspecies Varanus griseus caspius occurs from Iran to western Pakistan, and north through Central Asia as far as southern Kazakhstan, while Varanus griseus koniecznyi has the smallest and most easterly range, occupying eastern Pakistan and north-west India (2).

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Desert monitor habitat

Although predominantly desert-dwelling, the desert monitor occupies a variety of arid and semi-arid habitats including clay steppe, savanna and riverbeds up to elevations of 1,300 metres. A specific habitat requirement for this species is the presence of sand or soft soil in which tracks can be made for communication and orientation (2).

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Desert monitor status

Listed on Appendix I of CITES (1).

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Desert monitor threats

During the 1970s large numbers of desert monitors were hunted for sale within the international skin trade. This is believed to have caused significant declines in the population, leading to the listing of this species as Vulnerable on the 1994 IUCN Red List. Fortunately, following the introduction of trading legislation in 1975, hunting pressure has become far less intense, although local hunting and deliberate persecution of this species persists in some areas (2).

Today, the main threat to this species is habitat loss as a result of urban development and expansion of agriculture, which in some areas has caused the desert monitor to become rare or even extinct. Although a degree of habitat modification may be tolerated, major changes, such as the widespread conversion of steppe to cotton fields in Central Asia have proven to be catastrophic for this species’ survival (2).

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Desert monitor conservation

Since 1975, the desert monitor has been listed on Appendix I of the Convention on International Trade in Endangered Species (CITES), making all international trade in this species illegal (1). As a result, hunting pressure on this species has dramatically declined (1) (2). The desert monitor is widespread and considered to be abundant in some parts of its range, such as India and Pakistan, where its remote, arid habitat means that it is not greatly affected by urban development (2). In addition, the desert monitor’s global range encompasses several existing protected areas (5), as well as the proposed Umm Al Zummoul National Park in the emirate of Abu Dhabi (6).

Environment Agency - Abu Dhabi is a principal sponsor of ARKive. EAD is working to protect and conserve the environment as well as promoting sustainable development in the Emirate of Abu Dhabi.
View information on this species at the UNEP World Conservation Monitoring Centre.
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Find out more

To learn more about reptile conservation visit:

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Authentication

Authenticated (11/08/2009) by Yehudah L. Werner, Professor Emeritus of Zoology, Department of Evolution, Systematics and Ecology, The Hebrew University of Jerusalem.

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Glossary

Steppe
A biome (or subdivision of the Earth’s surface) that is composed of a swathe of temperate grassland stretching from Romania to China.
Subspecies
A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
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References

  1. CITES (March, 2009)
    http://www.cites.org
  2. Stanner, M. (2004) Varanus griseus. In: Pianka, E.R. and King, D.R. (Eds) Varanoid lizards of the world. Indiana University Press, Bloomington, Indiana.
  3. Hellyer, P. and Aspinall, S. (2005) The Emirates: A Natural History. Trident Press Limited, United Arab Emirates.
  4. Halliday, T. and Adler, K. (2002) The New Encyclopedia of Reptiles and Amphibians. Oxford University Press, Oxford.
  5. World Database on Protected Areas (March, 2009)
    http://www.wdpa.org
  6. Drew, C., Barcelo, I., Al Dhaheri, S., Al Hemeri, A. and Tourenq, C. (2005) A Proposal to Establish Umm Al Zummoul National Park. Environmental Research and Wildlife Development Agency, Abu Dhabi.
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Desert monitor in habitat  
Desert monitor in habitat

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