Comparative ecology of western grey kangaroos (Macropus fulginosus) and euros (M. robustus erubescens) in Durokoppin Nature Reserve, isolated in the central wheatbelt of Western Australia

Abstract

The populations of western grey kangaroos (Macropus fuliginosus) and euros (M. robustus erubescens) in a 1196-ha area of native vegetation in the central wheatbelt of Western Australia were studied over six years (1985-91). The area was isolated from other remnants of native vegetation by at least 1.4 km. Captures were made periodically throughout each year and the animals weighed and measured. In all, 152 animals were captured (83 euros and 69 western grey kangaroos). The data for each sex and species were assigned to 'seasons' (February-July or August-January) and assessments made of body condition. The weights and tail circumstances, adjusted for individual size by regression on leg length, were higher for western grey kangaroos but not for euros in August-January. Euro males varied significantly in weight from year to year; euro females and grey males and females did not. Too few grey females were captured to analyse seasonality of reproduction. The estimated birth dates of 68 euro pouch young were distributed equally throughout the study period. There were approximately equal numbers of each species in an estimate made in 1988 from a helicopter survey, with a total (± s.e.) of 191±29 kangaroos. The mean faecal pellet counts on 42 Tied transects of 100 m2 did not differ significantly over the period 1985-88. These counts showed that the overall use of the different vegetation types varied by a factor of two. Heaths had the highest pellet counts and open mallee or woodland the least, with Allocasuarina-dominated shrublands being intermediate. Spotlight surveys around the reserve boundary showed a highly significant difference in distribution of the two species. This was confirmed by analysis of the home ranges of 13 radio-collared individuals. Euros showed a strong preference for areas of York gum-wandoo-jam woodland with a herbaceous ground layer and areas with tall Allocasuarina or dense heath. In contrast, the western grey kangaroos preferred the heathlands and open woodlands without a herbaceous ground cover. The sex ratios of the whole populations seen in spotlight searches was 0.72 : 1.00 (males: females) for western grey kangaroos and 0.81 : 1.00 for euros. Both differ significantly from parity. There was a higher proportion of female euros amongst the animals seen in the western part of the reserve than in the eastern part. These populations relied mainly on the resources of the reserve. The average number of kangaroos seen on adjacent farmland on any one night varied from 3.6 in 1986 to 13.5 in 1991. A significantly higher proportion of males of both species were seen on farmland.