BEHAVIORAL INDICATORS OF ANXIETY - AN EMPIRICAL-TEST IN CHIMPANZEES

Behavioural, pharmacological, and physiological evidence supports an a ssociation between displacement activities and anxiety in macaques. In formation is scarce in other primate and non-primate species. This stu dy contributes to the understanding of the relation between displaceme nt activities and emotional states by investigating the correspondence between self-directed behaviour and an inherently stressful situation in chimpanzees (Pan troglodytes). Data were collected on 81 captive c himpanzees housed in conditions varying from indoor single caging to i ndoor/outdoor enclosures containing up to 14 individuals. Observation of gentle and rough scratching, self-grooming, and yawning were used t o test predictions concerning the response of individuals to neighbour vocalisation (i.e. the calls and noisy displays produced by neighbour ing groups of chimpanzees), which has been previously demonstrated to increase the likelihood of intragroup-agonistic behaviour. In socially -housed chimpanzees rough and gentle scratching and yawning were signi ficantly more common after neighbouring individuals vocalised or displ ayed than before, but the effect lasted longer for rough-scratching. I n addition, during periods characterised by higher levels of neighbour vocalisation, socially-housed chimpanzees performed rough scratching at higher rates. Self-grooming was not affected by the level of neighb our vocalisation. Single-caged chimpanzees, for whom neighbour vocalis ation carries no risk of aggression by group members, showed no increa se in self-directed behaviour when neighbour vocalisation level was hi gh, suggesting that the risk of intra-group aggression, rather than ne ighbour vocalisation itself, elicits anxiety. While our study suggests that rough scratching is the most reliable indicator of anxiety in ch impanzees in the context of neighbour vocalisation, it also provides e vidence that gentle scratching and yawning can be considered displacem ent activities in this species.