Social and spatial aspects of male subgrouping in a community of wild chimpanzees

Strong social bonds typically develop between dyadic pairs of male chimpanzees. These bonds are manifest in several contexts, including association, grooming, and proximity. Here we demonstrate that social bonds exist at a higher level of organization among males living in an extremely large community at Ngogo, Kibale National Park, Uganda. An analysis of over 2,500 hours of observation of 35 individuals revealed two distinct subgroups of male chimpanzees. Males that composed each subgroup can be identified on the basis of their tendency to associate in temporary parties. Matrix permutation tests indicated that subgroup members tended to maintain spatial proximity to each other and participate together in territorial boundary patrols. Subgroups formed along the lines of age and rank; members of a small subgroup were younger and lower ranking than individuals in a larger subgroup. Despite this social clustering of males, community integrity remained intact with low levels of aggression between individuals of different subgroups. After controlling for the effect of association, significantly more aggression occurred within compared to between subgroups. In addition, males of the different subgroups displayed significant overlap in their use of the community territory and thus showed no tendency to divide spatially. We compare our findings with those from other animal species and chimpanzee populations and discuss them in the context of the unusual demography of the Ngogo community.