Self-protective function of post-conflict bystander affiliation in mandrills.

Background: Affiliative interactions exchanged between victims of aggression and individuals not involved in the original aggression (bystanders) have been observed in various species. Three hypothetical functions have been proposed for these interactions: consolation, self-protection and substitute reconciliation, but data to test them are scanty.

Methodology/principal Findings: We conducted post-conflict and matched control observations on a captive group of mandrills (Mandrillus sphinx). We found that victims often redirected aggression to bystanders, that they received most affiliation from those bystanders that were frequently the target of redirection, and that bystander affiliation reduced the likelihood of redirection. Bystander affiliation did not reduce the victim's distress (as measured by its scratching rates) and was not received primarily from kin/friends. Finally, bystander affiliation did not reduce the likelihood of renewed aggression from the original aggressor.

Conclusions/significance: These results provide support for the self-protection hypothesis but not for the consolation and substitute reconciliation hypotheses.