Abstract
In March of 1991, the first-ranking male chimpanzee (Pan troglodytes schweinfurthii) was eliminated by other males from the M group in the Mahale Mountains National Park, Tanzania. Relationships among adult males were in disorder from February until June, when the former second-ranking male became dominant. This unstable situation enabled many adult males to approach estrous females without interruption by dominant males. Among thirteen females observed to be in estrous from February to June, males showed more eagerness to mate with three particular females. The three females were all middle-aged, multiparous, and had resumed sexual activity after weaning their latest offspring successfully. Judging from reproductive records for 25 years in Mahale, the age and reproductive careers of the three females signify higher potential for reproduction. When possible, male chimpanzees prefer to mate with highly reproductive females.
