Social stability via management of natal males in captive rhesus macaques (Macaca mulatta)

Keystone individuals are expected to disproportionately contribute to group stability. For instance, rhesus macaques (Macaca mulatta) who police conflict contribute towards stability. Not all individuals' motivations align with mechanisms of group stability. In wild systems, males typically disperse at maturity and attempt to ascend via contest competition. In a captive system, dispersal is not naturally enabled - individuals attempt to ascend in their natal groups, which can be enabled by matrilineal kin potentially destabilizing group dynamics. We relocated select high-ranking natal males from five groups and assessed group stability before and after. We quantified hierarchical metrics at the individual and group level. After removal, we found significantly higher aggression against the established hierarchy (reversals), indicative of opportunistic attempts to change the hierarchy. Mixed-sex social signaling became more hierarchical, but the strength of this effect varied. Stable structure was not uniformly reached across the groups and alpha males did not all benefit. Indiscriminate natal male removal is an unreliable solution to group instability. Careful assessment of how natal males are embedded within their group is necessary to balance individual and group welfare.