The Unitgroup of Wild Bonobos: By Instances of Inter-Unitgroup Encounters

Abstract

The social structure of unitgroup in wild bonobos (Pan paniscus) at Wamba, D.R. Congo is described. Fifty-nine instances of the inter-unitgroup encounter that were recorded from 1978 to 1991 were analyzed. Of these, the spatial fusion between two groups was observed in over 60%. During such encounters various affinitive behaviors, such as copulation, genito-genital rubbing and grooming e.g. were observed between members of different groups. In the inter-group encounters, females actively formed peaceful relations. Males interacted with members of the other group much less frequently than females. However, appeasement or assurance behaviors such as mounting and rump-rump contact merely occurred between males of different groups. Bonobos of two unitgroups coexisted peacefully in a mixed grouping, which eventually split into the original groups. The inter-group encounters may be an opportunity when young nulliparous females transfer to the other group. It is considered that the unitgroup of bonobos forms a stable structure of 30-50 members, and the fissions and fusions are repeated frequently among neighboring groups. These analyses suggest that bonobos have a regional society above the unitgroup level.