International Journal of Comparative Psychology

This study was conducted as a portion of a project investigating relationships among reproductive cycling, aggression, and wounding in captive chimpanzees. Changes in behavior associated with the genital swelling of 11 adult female chimpanzees socially housed in four different groups were measured using 282 hours of data gathered within a 20-month period. The females' perineal swellings were rated daily using a five-point scale indicating level of tumescence. Behaviors recorded when the animals were detumescent were compared with behaviors when their sexual swellings were maximal. In addition to the subject's genital swelling rating, two factors, the male-to-female ratio in the groups and the presence or absence of a tumescent female other than the focal animal, were also included in the analysis. Multiple regression analysis revealed significant effects of each of the three factors. Significantly higher levels of sexual behavior and lower levels of submission were associated with the tumescent stage of cycling. Scores for affiliation, aggression, abnormal behavior, inactivity, locomoting, and being followed did not vary significantly with swelling phase. Group structure (male-to-female ratios) affected affiliation, locomoting, being followed, and aggression levels. Affiliation, submission, and locomoting were influenced by the presence of a tumescent female in the group. Proximity to other adult females increased during the tumescent stage of swelling, but proximity to adult males did not change. The group structure and whether or not a tumescent female was present affected various aspects of proximity to all age/sex classes of group members. Some findings from this study may be explained by the long-term stability of group membership in the colony studied, and implications for colony management are discussed.