Sneaky hair-pulling to reinforce dominance in long-tailed macaques

Abstract Tactical deception is flexibly employed behaviour that is likely to be misinterpreted by a receiver. We initially observed one case where a long-tailed macaque seemed to show sneaky hair-pulling. To explore whether this behaviour may concern tactical deception, we gathered other instances of this behaviour and explored whether hair-pulling was also done in a sneaky way and should be classified as aggression, reinforcement of dominance, teasing or abnormal behaviour. We videotaped social behaviour in two multi-generational groups of long-tailed macaques and occasionally observed hair-pulling ( ) or attempts at hair-pulling ( ). Hair-pulling was not accompanied by signals of aggression. The actor of hair-pulling was dominant to the receiver in 16 of 17 cases. The hair-pulling was unexpected for the receiver and was executed differently in the two groups. In the Roza group, in nine cases a dominant individual sneaked up behind a subordinate and (aimed to) pull(ed) hair from its back, consistent with ‘hiding from view’ tactical deception. In the Haas group, in five cases the actor and receiver were in friendly contact, consistent with ‘presenting an affiliative image’ tactical deception. Altogether, long-tailed macaques seem to use group-specific sneakily performed hair-pulling to reinforce dominance.