CAPTIVE CHIMPANZEE--NEIGHBOR & GROUPS INFLUENCE AGONISTIC BEHAVIOR & ANXIETY

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SPID#: 63 The influence of calls and displays produced by neighboring groups ('external noise') on the behavior of 81 adult and juvenile chimpanzees (Pan troglodytes) was assessed from 219 hours of behavioral data. Higher rates of hooting, bluff displays, and agonistic behavior were found when levels of external noise were high. Incidents of external noise were directly responsible for such an increase intragroup agonism was significantly more common after neighboring individuals vocalized or displayed than before. This effect is congruous with behavioral patterns observed in the wild, and is therefore considered an expression of species-typical behavior as opposed to an artifact of captivity. External noise is likely to produce uncertainty among members of social groups because of the increased risk of being the target of agonistic behavior. It is therefore a useful tool for examining the relationship between anxiety and behaviors that have been previously reported as displacement activities in other primates (scratching, self-grooming, and yawning). Single-caged chimpanzees, for whom external noise carries no risk of aggression by group members, showed no increase in self-directed behavior when external noise level was high. Socially-housed chimpanzees, however, showed a correspondence between levels of rough scratching and external noise. Incidents of external noise produced an immediate effect on levels of rough scratching, as well as gentle scratching and yawning. However, the effect on rough scratching persisted longer after neighboring individuals vocalized or displayed. No association was found between self-grooming and the stressful situation investigated here. This study suggests that rough scratching is the most reliable and sensitive indicator of anxiety in chimpanzees, and that gentle scratching and yawning can be considered displacement activities in this species.