Food Transfer in Sichuan Snub-nosed Monkeys (Rhinopithecus roxellana)

Food transfer behavior provides a way to distribute food resources among individuals. It is not confined to kin, but also occurs among genetically unrelated individuals. Food transfer among nonkin may result from byproduct mutualism, reciprocal altruism (RA), or tolerated scrounging (TS). Sichuan snub-nosed monkeys (Rhinopithecus roxellana) exhibit a high level of social tolerance, and researchers have observed food transfer behavior in the wild. However, little is known about how tolerant social relations influence food transfer in this species. We recorded food-related interactions and social behavior in a group of captive Sichuan snub-nosed monkeys. Our findings suggest that the monkeys develop partner preference in food transfer behaviors. Moreover, individuals rely primarily on nonharassed approaches to claim food, suggesting that the TS model alone cannot explain their food transfer. Food transfer in this species may be a form of mutualism, in which an individual benefits on an immediate basis by fostering a preferred and tolerant relationship. However, we cannot rule out the possibility of reciprocal altruism. Future studies should record the temporal delay of social exchange to distinguish between mutualism and reciprocal altruism.