Ecology of the Pygmy Goanna (Varanus Brevicauda) in Spinifex Grasslands of Central Australia

Abstract

The reproductive biology, growth, movements, density and habitat use of Varanus brevicauda are presented. V. brevicauda is the smallest extant species of goanna. It is an inhabitant of the spinifex grasslands of central and western deserts and is rarely seen, so little is known of its ecology. Reproductive biology was determined from dissection of preserved museum specimens. Other ecological data were collected over three years from 111 V. brevicauda captured in pit-traps on a spinifex-dominated sand-dune environment in central Australia. V. brevicauda breed in spring when males have enlarged testes (July-November) and females are developing eggs (October-December). Clutch sizes of 2-3 eggs were found, but clutch sizes of 4-5 eggs have been reported. Eggs hatch from late January to February and neonates have a SVL of 42 mm. Sexual maturity, determined from preserved museum specimens, occurs at about 70 mm SVL for males, and 83 mm SVL for females, but small sample sizes for females make this estimate unreliable. The von Bertalanffy equation modelled growth in V. brevicauda better than logistic-by-length or logistic-by-weight equations. Parameter estimates for the von Bertalanffy equation are asymptotic body size (a) = 101.6 +/- 1.4 and characteristic growth rate (k) = 0.0029 +/- 0.0003. Males may grow to sexual maturity by their first spring at an age of 10 months, and females are unlikely to be sexually mature until their second spring at 22 months of age. V. brevicauda appear to be relatively sedentary with average displacements of 14-25 m over time intervals of up to 751 days. V. brevicauda were most abundant on the crests of sand dunes where densities were about 20 adults per ha. This abundance is surprising given the rarity of casual sightings. V. brevicauda is unusual compared with other sympatric species of Varanus because it is secretive, relatively sedentary and apparently abundant.