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Varanus brevicauda Print E-mail

Short-tailed goanna

Extract from A Little Book of Monitor Lizards © D. Bennett 1995. Viper Press, UK

Varanus brevicauda Boulenger 1898

The short-tailed goanna is the smallest living monitor lizard, and quite possibly the smallest species that has ever existed. They live in desert regions of Western Australia, Northern Territory and Queensland, most often in areas of spinifex. Maximum size is 23cm (12cm SVL) and gravid females may weigh as much as 20g. A specimen 9.9cm SVL caught in January weighed 9.5g. (Gow 1981; Storr & Hanlon 1980; Storr & Hanlon 1985; Pianka 1972, pers.comm.). Females tend to be smaller than males.

Very little was known about this delightful little lizard until recently (James 1996). Although they are found over a wide area comparatively few specimens are known from museum collections and the animals are very rarely seen. In the Great Victoria Desert they may be most active between November and January. Short-tailed goannas live in burrows or shelter under stones. In captivity they dig extensively. Like other dwarf monitors they feed on lizards and invertebrates (orthopterans, beetles, caterpillars and termites). However their diminutive size restricts them from feeding on many lizards and invertebrates form the bulk of their prey. They also feed on lizards' eggs, suggesting that they hunt for prey below ground. In captivity the short-tailed monitor is known to habitually grasp the tails of geckoes it is unable to overpower and swallow them when they are cast off. An active body temperature of 35.4oC has been reported (Slater 1964; Pianka 1970, 1994; Schmida 1974).

The short-tailed goanna is very common on dune crests in the spinifex grasslands of central Australia, but its wariness means that it is only rarely seen. James (1996) caught 111 specimens in pit traps and was able to make estimates of population size, growth rates and movement patterns for this extremely secretive lizard. In spring densities of up to 19 lizard per hectare were recorded, in Autumn no more than 6 per ha. were found. Most lizards that were recaught lizards were found within 20m of their last location the previous year, but one individual moved 400m. This suggests that at least some specimens are sedentary and spend most of their life in the same place. Mating occurs in September and October after hibernation and eggs hatch by February. Usual clutch size is 2 or 3 but in some coastal areas up to 5 eggs are produced. In dry years when food is scarce no reproduction occurs at all. In their natural environment hatchlings of 4cm SVL reach 7-8cm within a year. In captivity growth rates may be much faster. Whiles males become mature at around 7cm SVL females may mature at a larger size (8cm). Therefore it is possible that males reach maturity in their first year of life whilst females do not start to reproduce until their second year.

This species has been bred in captivity (Schmida 1974, 1985). An enclosure of .7m2 with a deep sand substrate is suitable. Light cycles and temperatures should fluctuate seasonally. Breeding coincides with the return of warm weather. Incredibly, females are capable of producing up to eight eggs (in three clutches) over six months. Eggs hatch after 42-85 days at temperatures of 18-25oC. Hatchlings measure less than 8cm TL and weight less than 3g. Sexually maturity is attained around 8-9cm SVL. In captivity they can grow to adult size within two years. Short-tailed monitors are reported to be somewhat fussy in captivity; they will not take dead prey nor will they eat even the smallest mammals (Greer 1989).

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