The effects of fur rubbing on the social behavior of tufted capuchin monkeys

Fur rubbing has often been attributed as a social as well as a medicinal function in capuchin monkeys, yet to date there have been no studies investigating the effects of fur rubbing on subsequent group dynamics. Here, we report for the first time how social group cohesion is affected by fur rubbing in tufted capuchin monkeys. Fifteen captive capuchins were each observed six times for 45 min, three times following the provision of materials typically used for fur rubbing (onion) and three times following control food items (apple). When compared with the apple condition, monkeys significantly increased proximity to one another in the first 15 min of the onion condition, which is when most fur rubbing took place. Moreover, monkeys were more likely to spend time in groups when fur rubbing but less likely to spend time in groups when manipulating the onion in other ways. In subsequent periods monkeys were less likely to be in proximity to one another in the onion condition compared with the apple condition. Aggression between group members was elevated whereas affiliation was decreased throughout the onion condition. In short, capuchins spent more time further apart and engaged in more aggressive acts and shorter affiliative acts following fur-rubbing bouts. It is possible that these differences in behavior could be owing to differences in how the monkeys competed for and interacted with the items presented in each condition rather than due to fur rubbing as such. Alternatively, fur rubbing with pungent materials might interfere with olfactory cues used to regulate social interactions within a group and thereby cause increased levels of aggression.