Determinants of sexual behavior of Macaca arctoides in a laboratory colony

Copulatory behavior of wild-born individually caged laboratory stumptail monkeys (Macaca arctoides) was investigated. The monkeys were paired daily for 20 min, and altogether 536 pairings were observed. The influence of the female's menstrual cycle and social factors of male sexual activity was determined. The reactions of the other monkeys during a pairing, and masturbation behavior of the males were observed and described. It was found that when a male and female were paired daily their sexual activity remained on a rather constant and high level for months provided the pair could not see, touch, or smell each other between pairings. In these conditions the most common copulatory behavior consisted of 3-4 ejaculations. When the couple lived continuously in adjacent cages, which allowed them visual, tactual, and olfactory communication between pairings, the male ejaculated, on the average, only once during five successive pairings. Thus separation and reunion was potent in triggering sexual activity. When the couple was visually separated between sessions the male's sexual activity did not depend on the menstrual cycle of the female. The males initiated copulation and the females were always willing, except in later stages of pregnancy, to cooperate. All males masturbated to ejaculation and it was often triggered by copulation, masturbation, or any happening causing arousal in the colony. The females were never seen to masturbate outside of the heterosexual context.