Who, me? Can baboons infer the target of vocalizations?

Abstract

We describe a playback experiment designed to test whether free-ranging baboons, Papio hamadryas ursinus, recognize when a call is directed at themselves rather than at other individuals. Female subjects were played the threat-grunt of a more dominant female under one of two conditions: after they had been threatened by that female and after they had groomed with that female. Subjects showed a shorter latency both to look towards the speaker and to move away from the area after aggression than after grooming. In the 15 min following playback, subjects who had recently been threatened were less likely to approach their former opponents and less likely to tolerate those females' approaches than during matched control periods. In contrast, subjects were equally likely to tolerate approaches by the dominant signaller following postgroom trials and during matched control periods. Combined with results from previous experiments testing baboons' responses to ‘reconciliatory’ grunts, these results suggest that baboons make inferences about the directedness of vocalizations even in the absence of visual cues, and that the nature of prior interactions affects subsequent behaviour. When attending to vocal signals, baboons appear to take into account not only the signaller's identity and her probable subsequent behaviour, but also the target of her attention. The ability to integrate these cues may represent a first crucial step towards the recognition of other individuals' intentions and motives.