Social Hair Plucking's Associations with Other Behaviors and Its Health Considerations, in Captive Rhesus Macaques (Macaca mulatta).

Primate social hair plucking (SHP) has been posited to be prosocial or agonistic, though the health-associated concerns of SHP are less frequently explored. We studied SHP in seven mixed-sex groups of captive rhesus macaques (Macaca mulatta), at the National Biomedical Research Institute. We examined whether individual rates of SHP were associated with grooming, aggression, and socio-demographic characteristics. We also examined whether SHP rates were associated with alopecia, body condition, and hair cortisol concentrations. Rates of SHP production and reception were similar to grooming and aggression, yet exhibited directional rank flow similar to aggression with kin biases similar to those for grooming. SHP given was associated with shared kinship with a social hair plucker; putative evidence of social transmission. SHP received was associated with alopecia. SHP given was associated with hair cortisol concentrations in females, albeit with high uncertainty. SHP fits the description of an abnormal behavior, is defined by a function, shows characteristics upheld by prosocial and aggressive behaviors, and has health associations. Future research should develop a comparative framework of SHP across species to examine mechanisms and motivations.