The Behavioral Ecology of Chimpanzees

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At the Mahale Mountains, Tanzania, social behaviors of habituated chimpanzees were studied. Major discoveries are as follows : (1) Intense mother-offspring conflicts occurred when mothers resumed their postpartum estrus. Weaning infants were upset by mothers' weaning behaviors and protested with whimper-screams and/or violent temper tantrums when their mothers declined their requests of suckling or transport, supplanted their feeding sites, made off leaving them behind, or mated with males. Mothers reassured their infants by embracing, grooming and/or permission of incestuous mating if the infant is male. Mothers usually permitted to suckle or ride on their backs after prolonged requests by infants. Mothers frequently shared food when infants begged for it. Weaning infants interrupted mothers' mating by pushing themselves between mothers and their mates. The rate of sexual harassment by infants was the increasing function of the ages of mating partners of mothers. (2) Grooming among adult males tended to be reciprocal or mutual when they are of similar age. Young adult males tended to groom older males without being reciprocated even when the latters were lower-ranking. (3) The alpha male of the study group shared meat with particular past-prime males, but not with the second-ranking and other young higher-ranking males. He groomed with, and supported in conflicts, those males that he often gave meat. Thus, meat-sharing by the alpha male could be regarded as a coalition strategy. He also frequently shared meat with his mother and past and current mating partners. (4) Bones, hair and teeth of chimpanzees were found in the faeces of lions six times. This was the first record of predation on wild chimpanzees by non-human animals. (5) Within-group infanticide and cannibalism by adult males was observed in detail. (6) The number of intestinal parasites and the use of medicinal plants increased in the rainy season.