Many facets of self-directed behaviours in macaques

Abstract

Emotional states like anxiety are adaptive, assisting individuals during social uncertainty and threats. Humans can self-report anxiety, whereas in nonhuman animals, particularly in primates, it is commonly inferred from self-directed behaviours (SDBs) such as self-scratch, autogroom and yawn. These behaviours are often treated as interchangeable indicators of a single underlying dimension of anxiety, yet support for this assumption remains limited. Moreover, how variations in SDBs are shaped by demography, social interactions and status, and the broader social dynamics, are poorly understood. To address these knowledge gaps, we studied 13 macaque groups across six species spanning a despotic–egalitarian social style. Our findings revealed partial correlational consistency among the SDBs, where only self-scratch and autogroom positively correlated. SDBs differed in their associations with demographic and social variables: males yawned more than females, individuals receiving less aggression engaged in longer autogroom, dominance rank showed behaviour-specific patterns and alpha individuals yawned more frequently than others. Social style showed no consistent effects across behaviours. These results show heterogeneity in the expression of SDBs that cautions against treating them as equivalent measures of anxiety. While not demonstrating functional dissociation, we highlight the need for greater conceptual precision in using SDBs to infer emotions in primates.