The Behavioral Ecology of Chimpanzees.

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This study is based on the field work conducted mainly in Mahale, Tanzania in 1987. Sex and age differences in the behaviors of wild chimpanzees were our major concerns. (1) Female infants tended to be weaned earlier than male infants. Male infants protested against the copulations of their mothers more frequently and more strongly than did their female counterparts. Birth interval tended to be shorter when the previous offspring was female. These differences can be explained by sexual selection hypothesis. (2) Feeding behavior differed across ages: Older adult males picked fallen fruits more often than young adult or adolescent males. Full adult males rarely fed on ants. In contrast younger males often did so. The alpha male of the group showed remarkably high feeding rate. Metabolic efficiency and nutritional needs may mostly explain the age differences. (3) Old aged chimpanzees tended to be groomed far more frequently than to groom others. This shows the unique status of aged chimpanzees in the chimpanzee society.