The short-tailed monitor occupies arid regions of western Australia (Pianka 1969).
Biogeographic Regions: australian (Native )
Distribution: Australia (North Territory, Queensland, South Australia, West Australia)
Type locality: Sherlock River, Nickol (as Nicol) Bay, W. A.
The short-tailed monitor is the smallest of the Varanid lizards, attaining a maximum adult length of only 8 inches. Newly hatched short-tailed monitors look just like the adults, but weigh about 1 to 2 grams and are only 1 to 2 inches in total length (Pianka 1969). Like all monitors the short-tailed monitor has a long neck, well developed limbs with five toes on both fore and hind limbs, strong claws, and a powerful tail that cannot undergo autotomy (Cogger and Zweifel 1998). The body color is usually a drab olive to brown color with lighter ocelli on the trunk. It is nearly impossible to determine the sex of most monitors by their outward appearance and the short-tailed monitor is no exception, as it is monomorphic (Bartlett and Bartlett 1996).
Range mass: 8 to 10 g.
The preferred habitat of the short-tailed monitor is arid regions dominated by spinifex. Spinifex are perennial grasses that form dense clumps, up to several feet in diameter, consisting of a central dense complex lattice-work and numerous outwardly directed needle-like spines (Pianka 1969).
Terrestrial Biomes: desert or dune
The short-tailed monitor is strictly carnivorous. Unlike most lizards, monitors are active foragers with a very high metabolic rate. Monitors use their long forked tongue much like a snake to pick up chemical cues in the air. The tongue, when flicked out, draws in these chemical cues and transfers them to the Jacobson's organ where the cues are analyzed (Pough et al. 1998). The diet of the short-tailed monitor is composed primarily of insects, other arthropods, smaller lizards (especially of the family -Ctenotus-, Australian skinks), and like most other monitors, they will not turn down carrion (Bartlett and Bartlett 1996). However, any prey item that has a chance of fitting in the monitor's throat will be actively pursued and consumed. One short-tailed monitor was reportedly found with a -Ctenotus calurus- in its stomach that made up 16.5% of the monitor's total weight. The monitor is able to eat such large prey because it utilizes a technique for feeding called mesokinesis. Mesokinesis is the dislocation of the jaw to swallow prey larger than the head (Pianka 1969).
Life History and Behavior
The short-tailed monitor is oviparous. Short-tailed monitors exhibit internal fertilization. The male has paired intromittent organs known as hemipenes. Although the hemipenes are paired they are only used one at a time, depending on which is more convenient. The clutch size will vary from 1 to 4 eggs, with a clutch size of 2 being the most frequent (Pianka 1969). The female will dig a burrow in which to deposit her eggs. The eggs will hatch between 70 and 100 days depending upon incubation temperature. The hatchlings are precocial and grow quickly attaining maturity and adult length within the first year to year and a half (Bartlett and Bartlett 1996).
Although there is no special concern about the short-tailed monitor all monitors from Australia are protected under CITES. There has been no extensive pressure from the pet trade on the short-tailed monitor (Pough et al. 1998).
US Federal List: no special status
CITES: no special status
Relevance to Humans and Ecosystems
Economic Importance for Humans: Positive
While the short-tailed monitor does not have a positive economic value there is a slight scientific interest in how it deals with the arid conditions in which it lives (Pianka 1969).
The short-tailed monitor, or the pygmy goanna, (Varanus brevicauda) is the smallest living monitor lizard, and may be the smallest species of monitor that has ever existed with a maximum length of 25 cm. They live in desert regions of Australia.
The generic name Varanus is derived from the Arabic word waral ورل, which is translated to English as "monitor". The specific name is a combination of two Latin words: brevis meaning "short" and cauda meaning "tail".
The short-tailed monitor ranges throughout central Australia from the coast of Western Australia through the interior of Northern Territory and northwestern South Australia to western Queensland. This monitor burrows in compacted sandy loam and gravel, in areas dominated by spinifex (Triodia spp.). This terrestrial species is secretive and rarely seen active above ground; it is mainly encountered by digging up its burrow.
Pygmy goannas are highly active foragers in the wild. They eat insects and reptile eggs, spiders, scorpions, small lizards and occasionally frogs and even small snakes. These small monitors are bold and fierce predators, despite their size.
Mating occurs for this monitor lizard in September and October after hibernation, and by February, the eggs hatch. The clutch size usually is two or three, but in some coastal areas, up to five eggs are produced. "In dry years when food is scarce no reproduction occurs at all."
The main threat to short-tailed monitors is predation by larger animals.
- "Varanus brevicauda". Integrated Taxonomic Information System. http://www.itis.gov/servlet/SingleRpt/SingleRpt?search_topic=TSN&search_value=716504. Retrieved 26 August 2008.
- Cogger, Harold; Zweifel, Richard (1992). Reptiles & Amphibians. Sydney: Weldon Owen. ISBN 0-8317-2786-1.
- King, Ruth Allen; Pianka, Eric R.; King, Dennis (2004). Varanoid Lizards of the World. Bloomington: Indiana University Press. pp. 225–229. ISBN 0-253-34366-6.
- Pianka, Eric R.; Vitt, Laurie J. (2003). Lizards: Windows to the Evolution of Diversity (Organisms and Environments, 5). 5 (1 ed.). California: University of California Press. ISBN 978-0-520-23401-7
- Varanus brevicauda mampam.com
- Short Tailed Pygmy Monitor - Varanus brevicauda pilbarapythons.com
- Photo of Short-tailed monitor
- Cogger, H. (1967). Australian Reptiles in Colour. Sydney: A. H. & A. W. Reed, ISBN 0-589-07012-6
- King, Dennis & Green, Brian. 1999. Goannas: The Biology of Varanid Lizards. University of New South Wales Press. ISBN 0-86840-456-X