Boundary patrols and intergroup encounters in wild chimpanzees

Dp. Watts et Jc. Mitani, Boundary patrols and intergroup encounters in wild chimpanzees, BEHAVIOUR, 138, 2001, pp. 299-327
Citations number
Categorie Soggetti
Animal Sciences","Neurosciences & Behavoir
Journal title
ISSN journal
0005-7959 → ACNP
Year of publication
299 - 327
SICI code
Chimpanzees are among the few mammals that engage in lethal coalitionary ag gression between groups. Most attacks on neighbors occur when parties made up mostly of adult males patrol boundaries of their community's range. Patr ols have time, energy, and opportunity costs, and entail some risks despite the tendency of males to attack only when they greatly outnumber their tar gets. These factors may lead to a collective action problem. Potential bene fits include protection of community members, particularly infants; range e xpansion and increases in the amount and quality of food available; and inc orporation of more females into the community. Males may not share these eq ually; for example, those able to obtain large shares of matings may stand to gain most by participating in patrols and to lose most by refraining. De spite the attention that boundary patrolling has attracted, few relevant qu antitative data are available. Here, we present detailed data on boundary p atrolling and intergroup aggression in a chimpanzee community at Ngogo, Kib ale National Park, Uganda, that is unusually large and has more males than any other known community. Males there patrolled much more often, and patro l parties were much larger on average, than at two other sites for which co mparative data exist. Our findings support the argument that male participa tion varies along with variation in potential gains, in willingness to take risks, and in skill at handling these risks. Both the overall frequency wi th which individual males patrolled and their willingness to join patrols a s others set off on them were positively associated with variation in matin g success, in participation in hunts of red colobus monkeys, and in hunting success. Males patrolled relatively often with others with whom they assoc iated often in general, with whom they often groomed, and with whom they fo rmed coalitions in within community agonism. This indicates that they were most willing to take risks associated with patrolling when with others they trusted to take the same risks.