The annual reproductive cycle of the Barbary Ape (Macaca sylvana) in Gibraltar

Data collected in Gibraltar demonstrate that Macaca sylvana has both a sharply demarcated mating and a sharply demarcated birth season. The mating season begins in November and may last until March. Births occur between May and September, gestation being of five or six months' duration. The annual reproductive cycle of the Japanese macaque is strikingly similar to that of the Barbary Ape. Matings occur in both areas in the fall, a period of decreased daily temperature and day length. The mating season begins with an increase in rainfall in Gibraltar and with a decrease in rainfall in Japan. From the data presented it seems probable that decreasing day length is the most important ecological factor in the timing of the onset of mating in Barbary Apes and in Japanese macaques.