A Three‐Year Study of Mating Behavior in a Freeranging Band of Rhesus Monkeys

The mating behavior of a freeranging band of rhesus monkeys in an island colony near Puerto Rico was studied for three consecutive years. From approximately July through December females had repeated cycles of estrous behavior in which they associated closely with males, groomed with them, and engaged in copulation. About one—half of the females which conceived had postconception estrous periods, including copulation. The average number of estrous periods per female was two, each period lasted an average of 11 days, and most estrous cycles lasted about 28 days. An average of three males associated with a female during one period. Most females began breeding when they were three years old and there was no significant difference between the mating activity of females three, four, and five years old. Six—year—old females showed a definite increase in mating activity, and females seven years old showed a still greater increase. No significant increase was apparent after the females reached seven. The females' rank in the dominance hierarchy apparently had no effect on their mating activity. The quantity of the males' sexual activity was generally correlated with their dominance rank. The highest male was the most active by far, the first to become active, and the only male to form many exclusive consort relationships with individual females. Progressively lower ranking males were usually less active, but low—ranking males were active early and late in the mating season. The findings concerning average period and cycle length, number of males associating with females, and the relation between the males' rank and mating activity agree closely with those of C. R. Carpenter (1942) on Cayo Santiago in 1940. Though several promising lines of inquiry have been opened, much work remains to be done before we can explain the relation between rhesus mating behavior and its physiologic basis, or explain variations in reproductive periodicity.