Abstract

Population density and habitat structure have been identified as influencing grouping patterns in kangaroos, but the separate contributions of each factor have rarely been distinguished. Grouping was examined in the western grey kangaroo, Macropus fuliginosus, at Hattah-Kulkyne National Park, north-western Victoria, where the population exhibits marked changes in density throughout habitats that provide a range of cover. Group size and population density in each habitat were surveyed at two times of day and at roughly 2-monthly intervals from March 1983 until December 1985. Of the four major habitats, mallee and woodland offered moderate cover, whereas grassland and lake bed gave sparse cover. Visibility of kangaroo groups was highest in the sparse habitats, and was positively related to the size of the group, at least in the lower range of group sizes. At densities up to 40km-2, groups that formed in the sparse habitats were larger than the groups in the two habitats that offered moderate cover. Three habitats (lake bed, grassland and woodland) had more smaller and more larger groups than expected if group formation was a random process. Large males were seen alone more often than expected by chance in lake bed, and less often in moderate cover; females with young-atfoot were over-represented as singletons in all four habitats. The size and composition of groups recorded in this study suggest that the basic components of the social organisation of kangaroos are best discerned in habitats that carry a low population density, but that also provide the most cover.