Abstract
Some of the behaviour of rhesus monkeys, including mating, associating with males, and fighting, is related to seasonal variation, long-term reproductive cycles, and to the menstrual cycle of the females. There was a recognizable breeding season in the colony studied. No behavioural modifications were associated with ovulation, and maximum mating frequency occurred at an infertile stage of the cycle. There were striking behavioural changes associated with menstruation. It is suggested that the term oestrus is not very useful when applied to this species or others with comparable patterns of behaviour.