Why do chimpanzees hunt and share meat?

Wild chimpanzees, Pan troglodytes, frequently hunt and share meat. Despite widespread interest and considerable study, continued controversy exists regarding the factors that influence chimpanzee hunting decisions and meat sharing. Three hypotheses invoke the importance of ecological, reproductive and social factors. A nutritional shortfall hypothesis suggests that chimpanzees hunt to compensate for seasonal shortages in food availability. A second hypothesis argues that male chimpanzees hunt to obtain meat that they swap for matings. A third hypothesis proposes that males use meat as a social-tool to develop and maintain alliances with other males. We tested these hypotheses using observations of an unusually large community of chimpanzees at Ngogo in Kibale National Park, Uganda. Results did not support the nutritional shortfall or meat-for-sex hypotheses. The Ngogo chimpanzees hunted primarily during times of food abundance rather than scarcity. The presence of oestrous females did not predict the tendency of chimpanzees to hunt. Furthermore, meat-for-sex exchanges occurred infrequently, and males did not gain a mating advantage through sharing meat. Additional observations were consistent with the male social bonding hypothesis. At Ngogo, male chimpanzees were likely to hunt when accompanied by other males. Males shared meat nonrandomly and reciprocally among themselves, and males exchanged meat for agonistic support. Although several factors are likely to affect chimpanzee hunting decisions and meat sharing, these results indicate that primary causes will not be found through invoking simple energetic or reproductive considerations. (C) 2001 The Association for the Study of Animal Behaviour.