Female genital swellings have no effect on chimpanzee agonism in well-established group

Reducing the incidence of aggression and wounding is a major concern for those managing socially housed chimpanzees (Pan troglodytes ). Competition among adult males for access to sexually receptive females is believed to be one factor contributing to undesirably high levels of agonism. An observational analysis of two chimpanzee groups (n = 9, n = 8) was initiated to study this phenomenon. All-events sampling was used to record agonistic and sexual behavior on days when one female in the group showed a maximal genital swelling and on other days when no female in the group had a tumescent swelling. The results of the multivariate analysis of variance indicated that the presence of a female with a tumescent swelling had no effect on bluff displays or aggressive, submissive, or reconciliatory behavior but that sexual behavior was significantly increased. These results may be explained by the fact that long-term stability in group membership may reduce male-male competition for sexual access to females and the sometimes associated aggression and wounding.