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Watts / Poster

Demographic influences on the behavior of male chimpanzees

David P. Watts, Dept. of Anthropology , Yale University, New Haven, CT, USA 06511-8277

     The extent of cooperation and affiliation among male chimpanzees is unusual for mammals, as is the fact that males stay in their natal communities. Communities are based on cores of males who are hostile to males and anestrous females in neighboring communities. Resident males compete for fertilizations and dominance ranks, use alliances in this competition, and engage in complex alliance formation and maintenance strategies in which grooming is important. These characterizations seem typical across populations, but we have limited data on variation in the details of male competition, cooperation, and social relationships. Variation in demography, particularly in the number of males per community, ought to affect variation in male behavior strongly.
     I present data on an unusually large chimpanzee community at Ngogo, Kibale National Park, Uganda, that has far more adult males (24) than any other known community. I examine some effects of male number on behavior, and compare these data with some from other chimpanzee communities and with data on male mountain gorilla life history variation. These comparisons support the idea that demographic variation is an important influence on great ape behavior. Many males at Ngogo have dominance relationships with each other, and the community has had a clear alpha male during most observation time, but not a clear dominance hierarchy. Males form alliances and show reciprocity in agonistic support, grooming, and meat sharing; they appear to trade grooming for support. Like in smaller communities, most coalitions occur among a small subset of high-ranking males, but these males get at least occasional support from many partners. Individuals groom mostly with a limited set of potential partners, as if time limits constrain their ability to maintain grooming networks. The large number of males promoted cooperative mate guarding by several high-ranking males (an unusual mating tactic), but this cooperation proved unstable as alliances shifted. The large number of males also leads to extraordinarily high success in hunts of red colobus monkeys, the chimpanzees' main prey, and presumably explains the high frequency of boundary patrols.