Resumption of seasonal breeding patterns in male and female rhesus monkeys transferred from an indoor to an outdoor environment.

Seasonal aspects of social behavior and sex steroid levels were observed in two groups of rhesus monkeys from March through December. One group (3 males, 7 females) had lived outdoors for several years. The other group (6 males, 5 females), transferred outdoors in late February, had lived indoors for several years. In March-April, the long-term outdoor residents displayed the expected seasonal pattern of sexual behavior, characterized by absence of complete sequences of copulatory behavior. At this time the indoor-adapted group displayed high levels of copulatory behavior. Thereafter, frequencies of sexual behavior of the two groups were similar. Testosterone in the males was positively correlated with frequency of sexual behavior in each group. Females in the indoor-adapted group displaced menstrual cycles in March and April and 3 of 5 became pregnant at this time. The two remaining indoor-adapted females continued to display ovulatory cycles, but little sexual behavior, throughout the summer. Interestingly, two females in the outdoor-adapted group also displayed summer ovulatory cycles; without concomitant sexual activity. These data show that the disruption of seasonal breeding patterns produced by lengthy indoor housing remains briefly apparent following transfer outdoors, but is substantially overcome within a few months.