Can simple rules account for the pattern of triadic interactions in juvenile and adult female sooty mangabeys?

Several experimental and observational studies have investigated the pattern of triadic relationships in primates to demonstrate knowledge of third-party relationships (i.e. an individual recognizes the relationship that exists between two others). To date, all studies have investigated the recognition of third-party relationships in adult animals. Thus, we do not know whether juveniles have knowledge of third-party rank relationships or whether they use a set of simple rules until they learn the rank relationships of all animals within a group. Here, we present the first data on triadic interactions involving juveniles in a rainforest primate, the sooty mangabey, Cercocebus torquatus atys. In a group of 120 individuals, we found that (1) if two groomers were approached by an individual ranking higher than both, the higher-ranking member of the grooming dyad was significantly more likely to stay than the lower-ranking one; (2) when an animal intervened in a conflict, juveniles and adult females were significantly more likely to support the higher-ranking contestant; and (3) juveniles and females solicited help in conflicts significantly more often from potential allies that outranked them and their target than from allies that ranked below them and/or the opponent. Our results suggest that the triadic interactions of juvenile sooty mangabeys resemble triadic interactions reported for adult members of other species of Old World monkeys, but that most of the observed behaviour patterns could be explained by a set of simple rules instead of invoking higher cognitive abilities.