Social dynamics among females and their influence on social structure in an East African chimpanzee community

Social structure in group-living animals is defined by the nature and patterning of social interactions among members of the society. Social structure is shaped in large part by kinship and competition among group members, but can also be influenced by affiliative interactions among both kin and nonkin and can vary based on sex differences in dispersal patterns and social dynamics. Chimpanzees, Pan troglodytes, live in fission–fusion societies in which males form strong dyadic bonds and have social networks that can influence the social structure of the community. Females are generally less gregarious than males and bonding among females is considered rare or absent in East African populations. Although females in some populations are known to form ‘neighbourhoods’, these are assumed to reflect passive spatial arrangements. In this study I used data on female chimpanzee association and social interactions to examine how social dynamics among the dispersing sex influence social structure at Ngogo, Kibale National Park. Females at Ngogo were relatively gregarious and exhibited association preferences that extended beyond the dyadic level. Females formed distinct association clusters termed ‘cliques’ within which affiliative interactions occurred more than expected by chance. In addition, association patterns were found to be active social units and not a by-product of space use overlap. These findings demonstrate that intrasexual bonding is not limited to males in this population and that female social relationships, not just those of males, can influence chimpanzee grouping patterns and the corresponding social structure of the community. This study contributes to our growing understanding chimpanzee behavioural diversity.