Seasonal variability in spatial defence by free-ranging rhesus monkeys (Macaca mulatta)

Data on the rhesus monkeys (Macaca mulatta) of Cayo Santiago demonstrate both intergroup and seasonal variability in spatial defence. Of the five groups only one defends an area, and only during the birth season. The four non-defensive groups share two feeding stations and live in such close proximity that spatial defence would require high outputs of energy. In contrast, the group that maintains an exclusive area has its own feeding station and lives in semi-isolation on an easily defensible end of the island. Its defence of this end of the island during the birth season provides a protected area for infants and assures the group exclusive access to flowering and fruiting plants. Relaxation of this defensive behaviour during the mating season maximizes opportunities for intergroup matings.