Age differences in the duration of mating period of female rhesus monkeys

Examination of the patterns of mating behavior exhibited by 27 sexually-mature female rhesus monkeys housed in a social group in an outdoor compound revealed that younger animals (3.5-4.5 years) exhibited significantly longer periods of sexual activity than did older animals (5.5 years and older). Observed sexual activity in all age groups was largely confined to discrete periods associated with an ovulatory cycle and typically resulted in pregnancy. Related findings suggest that differences in patterns of sexual behavior may be related to variations in estrogen secretion or sensitivity to estrogen, both of which show age-related changes. Additionally, these findings underscore the importance of documenting behavioral and endocrine changes in reproductive function across the full life span of the mature subject.