Hierarchy and social status in Budongo chimpanzees.

The status hierarchy is fundamental in the lives of male chimpanzees. This study describes the dominance interactions and social status among adult male chimpanzees of the Sonso community in the Budongo Forest Reserve, Uganda, during the period that they were first studied (1994 and 1995). Social dominance is typically measured using the behaviour of either the subordinate or the dominant individual, but a relationship is dependent on the behaviour of both parties and this study explicitly used both subordinate and dominant behaviours to investigate the status hierarchy. Among adult males of the Sonso community, agonistic interactions occurred at a low rate and pant-grunts were rare, but males could be ranked into separate hierarchies of agonistic dominance and pant-grunting (labelled 'respect') using ratios of behaviour performed/behaviour received. These hierarchies were combined to form a single hierarchy of social status that divided the males among five distinct status levels. The highest status level was held by an alliance between two males who replaced the previous alpha male during the first part of the study. Neither male in this alliance partnership pant-grunted to the other, although the reason for cooperative behaviour was unclear. Although the nominally beta male was treated as such by other adult males, he achieved surprisingly little mating success. Budongo Forest chimpanzees do not warrant the sometimes-expressed view that they are non-aggressive and peaceable and the broad pattern of their status interactions matches with that seen in other chimpanzee populations.