Many facets of self-directed behaviours in macaques

Emotional states like anxiety are adaptive, assisting individuals during social uncertainty and threats. While humans can self-report anxiety, assessing comparable states in animals requires objective measures. Self-directed behaviours (SDBs), including self-scratch, autogroom, and yawn, are indicators of anxiety, particularly in nonhuman primates. Yet it is unclear whether they reflect a common underlying process or distinct responses shaped by demography, social interactions and status, and the broader social dynamics. We studied 13 macaque groups across six species along a despotic-egalitarian social style gradient to investigate the factors associated with variation in SDBs. Our findings revealed partial correlational consistency among the SDBs, where only self-scratch and autogroom positively correlated. Further, we found that males yawned more than females, and individuals receiving less aggression exhibited longer autogroom bouts. Dominance rank showed behaviour-specific effects, with weak evidence for an association with self-scratch, longer autogrooming in subordinates, and a non-linear pattern in yawning, which was lowest at intermediate ranks. Alpha status was linked to more frequent yawning than others. And finally, social style showed no consistent effects on SDBs. Our research demonstrates that SDBs in macaques reflect differential responses related to social uncertainty rather than one anxiety dimension, providing insights into primate emotion regulation.