During females ' menstrual cycle there is usually a visible change in the genital area, a red coloration. Males' testes become enlarged and the naked skin of the posterior takes on a redder color also. Mothers nurse their young for 7-14 months. Like human babies, Rhesus babies seek physical contact with their mothers. This is needed for normal emotional development of infant monkeys.
Males leave their group and migrate to a new one at a young age for mating purposes.
Rhesus macaques were used as early space travelers to test the physiological effects of space. The RH blood factor, present in man but first identified in the rhesus monkey, is named for it. Psychological testing shows their ability to use symbols. Grzimek's Encyclopedia, Mammals Vol.