Old age and its behavioral manifestations: a study on two species of macaque.

Observations from two studies on the behavior of stumptail and Japanese macaques revealed that old females were generally less active and involved in fewer social interactions than young adult females. Old females typically avoided or maintained sufficient distance from others to decrease the possibility of interaction, but were neither excluded from social interactions nor out-competed in rank-related situations. The data strongly suggest that the old females selectively withdrew from social interactions and maintained their rank over younger members of the group. Three possible explanations are discussed for the differences in behavior between old and young adult macaque females. (1) Old females with older offspring are less likely to interact with others than old females with younger offspring; (2) old females obtain fewer benefits from social interaction than young adult females, and (3) older females have less energy to disburse for social interaction due to physiological deterioration. The age of the youngest offspring did not account for the decline in social interactions among old females. It was concluded that active withdrawal from social interactions on the part of old females is likely to be the result of both a decrease in the benefits obtained from sociality and an overall physiological deterioration.