Provin, A. | Search bioRxiv

bioRxiv2026

Risk management strategies in social grooming among Tonkean and rhesus macaques

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.

animal behavior and cognition↗

bioRxiv2026

A Social Affordance Framework for Understanding Approach Decisions in Wild Crested Macaques (Macaca nigra)

Approaching conspecifics is a fundamental component of social interactions. Such decisions are typically investigated through the study of social relationships (e.g., kinship, dominance, affiliation) and their impact. In the framework, the role of social affordances, i.e., interaction opportunities arising from the immediate social environment, remains poorly understood. We investigated how context-dependent factors shape approach decisions in wild crested macaques (Macaca nigra) in North Sulawesi, Indonesia. From September 2024 to May 2025, we collected data on 27 adults (20 females, 7 males) using focal observations and an approach-specific protocol recording neighbours identities and behaviours at the initiation of close-proximity approaches (<1 body length). We first compared data collected during approaches with focal data, then conducted within-approach analyses contrasting approached partners and bystanders. We further tested the effects of behavioural state, subgroup size and composition, including infant presence. Bayesian models revealed that affiliative, neutral, and grooming behaviours were more frequent in approach contexts than in general observations. Within approaches, individuals avoided congeners already engaged in grooming and approached individuals in neutral or affiliative states (e.g., lip-smacking, embracing). Macaques globally approached more isolated individuals or dyads. When multiple subgroups were present (i.e., multiple choices), the likelihood of being approached increased with subgroup size and was higher in subgroups containing infants. These findings indicate that macaques use behavioural cues and local social density as affordance signals, adjusting approach decisions to maximize interaction opportunities and navigate complex social environments.

animal behavior and cognition↗