The Sexual Behavior of a Confined Troop of Japanese Macaques

The sexual behavior of a confined troop of 69 Japanese macaques was observed throughout its 5 months breeding season. Males 2½ years of age and older mounted adult females but only males 4½ years and older ejaculated. All females 3½ years of age and older were sexually receptive and all but two of the adult females conceived. The frequency and intensity of mating was somewhat related to dominance in males, to age in both sexes and to the recency of an offspring in females. All males mated, some of the most active being low in rank; however, the most dominant males ejaculated more frequently. Middle-aged females were very active throughout the season; females with recent infants were least active. The frequency, the intensity, and the types of behaviors exhibited by females during the season showed no consistent cyclic fluctuations. The continued sexual activity of pregnant females, the higher numbers of ejaculations and the displays of high-ranking males, and the repeated mounting of mature females by nonejaculating males demonstrate the social nature and essentially nonprocreative functions of much breeding season activity. The interaction between hormonal and social factors must be considered in the approach to an eventual understanding of sexual behavior in primate species.