Variations in Group Size and Composition in Red and Western Grey Kangaroos, Macropus rufus (Desmarest ) and M. fulignosus (Desmarest)

Data on group size and composition in red and western grey kangaroos are analysed with respect to population density and season. In red kangaroos, typical group sizes were correlated with density at all times of the year. Analyses of density-group size relationships in each sex showed female typical group size to be correlated with female density but male densities and group sizes to be uncorrelated. Small adult males were the least likely to be with near-oestrous females, and apparently tend to disperse into suboptimal habitats. In the seasonally breeding western grey kangaroos, densities and typical group sizes were correlated during spring and summer, but not during autumn and winter, when groups tended to be larger. This seasonal shift is mainly due to changes in the grouping behaviour of males. These patterns are interpreted as being due to dominance relationships and seasonal reproductive strategies of males.