The communicative function of stress behaviours in macaques

In humans and non-human animals, stress is often linked to observable behaviours (e.g scratching, self-grooming and other self-directed behaviour). Although the link between stress and these behaviours is a widely accepted phenomenon, their adaptive value remains understudied and consequently, the reasons for their production are unclear. Stress behaviours are often derived from behaviours that are highly visual (e.g. scratching, yawning, selfgrooming), and it has been hypothesised that these behaviours may provide information to others via a signal. In this thesis I aim to test this hypothesis, that a stress-behaviour (scratching) has a communicative function, in a nonhuman primate model genus, the macaques (Macaca). Firstly, I consider how observers perceive the scratching of others, and more specifically, how they are perceived in comparison to neutral, noncommunicative behaviour. The findings of this first study demonstrate that macaques attend to the scratching of others more so than neutral behaviours, with this shift in attention being modulated by the degree to which the subject is bonded with the actor. Secondly, I consider how the macaques respond to the stress of others, comparing social interactions with and without a preceding scratch. The findings of this study demonstrate that producing stress behaviour had significant impact of the likelihood of aggressive from others, and led to more harmonious interactions. Finally, we consider the function of scratching during two other contexts, preceding behavioural change, and as a signal during grooming interactions, however, we find no evidence for a communicative function of scratching in either of these contexts. Overall, this thesis supports the idea that stress-behaviour is perceived and responded to by others, providing some of the first evidence to suggest that these behaviours may function communicatively. Ultimately, these data adds some further clarity as to why stress behaviours have evolved, and why they exist in the behaviour repertoire of many social animals (including ourselves).