Grouping patterns show subtle social structure in a species with strong fission-fusion dynamics (#383)
Eastern grey kangaroos Macropus giganteus are gregarious, with females mostly philopatric and most males dispersing. Females are thus assumed to form kin clusters but details of associations among different sex-age classes in this species are largely unknown. We observed 153 marked kangaroos at Wilsons Promontory National Park, Australia. We examined relationships within and between six different sex-age classes using half-weight indices and lagged association rates. We found subtle social structure. Mean half-weight indices were similar within compared to between different sex-age combinations. For adult females, there was a weakly positive relationship between pairwise relatedness and dyadic half-weight indices but this effect disappeared after controlling for geographic distance or spatial overlap. Lagged association rates decreased exponentially only for adult males with adult females accompanied by young-at-foot in the breeding season. Most other lagged association rates decreased slightly in a linear fashion and few were constant. Although females without young-at-foot appeared to be more social than females with young-at foot, all associations among individuals were weak. Contrary to expectations, the social structure of kangaroos was not based on female relatedness at high density under strong fission-fusion dynamics.