Sexual initiation in wild mountain gorillas

Abstract

A field study of wild mountain gorillas was conducted to elucidate details of sexual initiation required for an interpretation of the increased frequency of copulation during the menstrual cycle, in comparison to the wild, that occurs when this species is tested in traditional laboratory pair tests. Although females in the wild played a clear role in establishing and maintaining proximity to the male and assertively presenting for copulation, all female presenting was preceded by some form of behavior by the male. Of particular relevance were several components of the male’s chest-beat display that had been observed at much higher frequencies in the laboratory tests. Although originally described as male aggression in the laboratory tests, such behavior now appears to be male sexual initiative, elicited by female proximity. The exaggerated form and frequency of the display in the laboratory, and the increased copulation during the cycle that ensued, are likely due to (1) placing females in proximity to a male daily, rather than on 2–3 days of estrus as occurs in the wild, and (2) the inability of the female in the laboratory to withdraw from male proximity during pair tests in a single cage. In addition to clarifying the data on laboratory pair tests, the data on wild gorillas have relevance to the captive breeding of gorillas.