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.