Who's there? Third parties affect social interactions between spider monkey males

Spider monkeys provide an intriguing opportunity to examine behavioural flexibility in relation to their social environment given their high degree of fission fusion dynamics and the nature of male male relationships. These characteristics allow us to examine how flexibility in social interactions is modulated by the perception of risk and uncertainty related to other group members. We investigated whether male male interactions vary according to partner identity and presence of third parties in wild Geoffroy's spider monkey (Ateles geoffroyi). We used proportion of approaches followed by an embrace, an indicator of risk and uncertainty, or by grooming, an affiliative behaviour To confirm the monkeys' perception of risk or uncertainty we used aggression rates and time spent We collected data on eight adult spider monkey males: three of them belonged to one clique and the other live to another clique based on distinct patterns of residence. We found higher proportions of approaches followed by embraces and lower proportions of approaches followed by grooming between males of different cliques than between males of the same clique. In addition, we found higher aggression rates between males from different cliques. The proportions of approaches followed by embraces in the five-male clique were higher when the three-male clique was no longer in the group. The live males were more vigilant when the other three males were present in the group, indicating the monkeys perceived higher risk or uncertainty under these circumstances. We found lower proportions of approaches followed by grooming between two males when there was at least one other male in the subgroup than when there were only the two males. Our results provide evidence for behavioural flexibility in the interactions between spider monkey males as an example of how animals can cope with social challenges by adjusting then behaviour.