Short-tailed pygmy monitor
| Short-tailed pygmy monitor | |
|---|---|
Scientific classification 
| |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Order: | Squamata |
| Family: | Varanidae |
| Genus: | Varanus |
| Subgenus: | Odatria |
| Species: | V. brevicauda
|
| Binomial name | |
| Varanus brevicauda Boulenger, 1898
| |
The short-tailed pygmy monitor (Varanus brevicauda)[1] is the second smallest living monitor lizard in the world with a maximum length of 25 cm.[2]
Geographic Range
The short-tailed monitor occupies arid regions of western Australia
Habitat
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.
Physical Description
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.
Reproduction
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.
Behavior
Like most monitors, the short-tailed monitor is solitary in nature and avoids contact with other monitors, especially those that are bigger and could be a predator. However, due to the fact that short-tailed monitors are so small and mainly live in burrows it is not uncommon to find a very large population in a very small area (Pianka 1969). These monitors are very active diurnal foragers. The short-tailed monitor has a very keen sense of sight and hearing but attains the bulk of its sensory information through chemical signals picked up by the Jacobson's organ. These signals include mate recognition and competitor recognition. During the breeding season males will engage in combat for the right to mate with a female. The males will raise up on their hind limbs supported by their tails and wrestle until one is thrown to the ground.
Food Habits
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.
Geographic Range
The short-tailed monitor occupies arid regions of western Australia.
Distribution
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.[4] This monitor burrows in compacted sandy loam and gravel, in areas dominated by spinifex (Triodia spp.). This terrestrial species is secretive[5] and rarely seen active above ground; it is mainly encountered by digging up its burrow.[4]
Diet
Short-tailed pygmy monitors are highly active foragers in the wild.[6] They eat insects such as grasshoppers, beetles, roaches, caterpillars, as well as reptile eggs, isopods, spiders, scorpions, small lizards and occasionally frogs and even small snakes.[7][4] These small monitors are bold and fierce predators, despite their size.[6]
Reproduction
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."[5]
Conservation
The main threat to short-tailed pygmy monitors is predation by larger animals.
References
- ^ a b "Varanus brevicauda". IUCN Red List of Threatened Species. 2018. 2018. Retrieved 2021-02-14.
{{cite journal}}: Unknown parameter|authors=ignored (help) - ^ Cogger, Harold; Zweifel, Richard (1992). Reptiles & Amphibians. Sydney: Weldon Owen. ISBN 0-8317-2786-1.
- ^ Herman, John. "Varanus brevicauda (Short-tailed Pygmy Monitor)". Animal Diversity Web. Retrieved 2021-07-15.
- ^ a b c Pianka, Eric R.; Vitt, Laurie J. (2003). Lizards: Windows to the Evolution of Diversity (Organisms and Environments, 5). Vol. 5 (1 ed.). California: University of California Press. ISBN 978-0-520-23401-7.
- ^ a b Varanus brevicauda mampam.com
- ^ a b Short Tailed Pygmy Monitor - Varanus brevicauda pilbarapythons.com
- ^ Losos, Jonathan B.; Greene, Harry W. (1988-12-01). "Ecological and evolutionary implications of diet in monitor lizards". Biological Journal of the Linnean Society. 35 (4): 379–407. doi:10.1111/j.1095-8312.1988.tb00477.x. ISSN 0024-4066.
- 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