Population dynamics of the common wallaroo (Macropus robustus erubescens) in arid New South Wales

Abstract

The population dynamics of the common wallaroo or euro (Macropus robustus erubescens) were investigated in two adjacent sites in far western New South Wales. Wallaroo densities were generally higher in a site of high relief (South Ridge) than in one of low relief (South Sandstone); however, both sites exhibited large fluctuations in numbers (ranges of 2.23-18.31 per km*2 and 3.48-19.99 per km*2, respectively). The proportion of adult males relative to adult females was significantly higher in South Sandstone (c. 1.1 : 1) than in South Ridge (c. 0.4: 1), indicating a difference in habitat usage by the sexes. At both sites, fluctuations in overall density were best explained by changes in the density of adult females; however, the relative importance of changes in the numbers of other size-sex classes in determining density fluctuations differed between the two sites. Total density was significantly related to the previous rainfall regime in South Ridge but not in South Sandstone. Reproductive condition of females and survivorship of young were related to environmental conditions. Adult mortality ranged from 4.55 to 25.81% per year and adult survivorship was positively correlated with the abundance of grass. Evidence is presented to support the hypothesis that dispersal of subadults is predominantly a male phenomenon.