Social organization of savanna-dwelling chimpanzees,Pan troglodytes verus, at Mt. Assirik, Senegal

Abstract

A community of chimpanzees at Mt. Assirik in south-eastern Senegal subsists in a hot, dry and open environment. This wide-ranging, savanna-living group provides an opportunity for comparisons of social organization with other population elsewhere in Africa living in forest and woodland. The group numbered about 28 over the four-year study, and its composition by age and sex was typical. The average size of parties (i.e., temporary sub-groups) did not differ from other populations. However, a high proportion of the group tended to remain together in such parties. The composition of parties resembled that found elsewhere, but some differences emerged between the wet and dry seasons. Larger, mixed parties containing adult males were much more common in open, non-forested habitats than were solitary individuals or parties without adult males. Large parties tended to form for travelling, especially for rapid movement over long distances. Such aspects of social organization seem unlikely to be related to the availability of food in any simple way. Instead, they seem to be adaptations to threat from predators and patchily distributed food, water and nesting sites. This results in occasional bivouacs and mass-migrations from one part of the home-range to another, especially in the dry season.