Risk management strategies in social grooming among Tonkean and rhesus macaques

Abstract

Group-living individuals interact constantly, maintaining cohesion, stability, and security within their social groups. However, these interactions can entail risks that individuals must manage to optimize their social navigation through complex social groups, such as those of non-human primates. Here, we investigated how macaques manage risk during social grooming by analysing its somatic modalities, including body orientation and body site being groomed. We compared two macaque species with contrasting social styles: the more despotic rhesus macaque and the more tolerant Tonkean macaque. Using dyadic analyses including species, kinship, age difference, rank difference, and male presence as predictors, we found marked species differences in grooming patterns. Tonkean macaques engaged more frequently in face-to-face grooming and less in face-to-back grooming compared to rhesus macaques. They also groomed body sites associated with high eye-contact probability, such as the head, neck, and chest, more often than rhesus macaques. Kin dyads groomed these body sites more often, particularly in rhesus macaques. These findings suggest that avoiding body sites associated with potential eye-contact may constitute a risk management strategy during grooming. Overall, our results reveal a previously overlooked dimension of primate social cognition that may shape dyadic relationships and social network structure.