Seasonal influences of births and male sex skin coloration in rhesus monkeys (macaca mulatta) in the southern hemisphere.

The annual distribution of births of rhesus monkey in zoos in the southern hemisphere and changes in sex skin coloration in one colony were examined. Most (79%) of the births occurred between October and January and the sex skin reached its greatest development during spring and early summer (i.e. at the time of mating). These results demonstrate a 6-month reversal from the breeding activity of rhesus monkeys in the northern hemisphere.