Sexual behavior of captive chimpanzees (Pan troglodytes): Pregnant versus cycling females.

Sexual behavior was observed in fifteen female and seven male captive adult chimpanzees over a period of three months. Relative frequencies of successful and unsuccessful copulatory attempts were compared to levels of anogenital swelling and reproductive status. In addition, the data were analyzed in relation to three indicators of female primate sexuality: (1) proceptivity, indicated by female attempts at sexual interaction; (2) attractivity, indicated by male-initiated attempts; and (3) receptivity, evident when a female responds positively to male initiation. The data suggest that increased level of anogenital swelling enhanced female proceptivity and attractivity, but not receptivity. Comparison of cycling vs pregnant females revealed that attractivity and receptivity increased during pregnancy, while proceptivity was relatively unchanged. The total success rate (copulations/attempts) was 63.3% (42% for female-initiated attempts and 77% for male-initiated attempts). Pregnant females copulated at a high rate, almost double that of cycling females. Sexual activity during pregnancy and the occurrence of anogenital swelling during pregnancy are discussed in terms of female reproductive strategies.