Résultat de la recherche
The ontogeny of pant hoot vocalisations and social awareness in wild chimpanzees
While some scholars have regarded primate vocal communication as innate, inflexible, and insensitive to the context, recent advances suggest instead that vocal behaviours can be flexible, insofar as they are affected by individual and situational factors, notably the social context. However, whether the same is true for the acquisition of communicative capacities remains largely unknown, particularly in great apes. In my thesis, I address this by examining the ontogeny of vocal behaviours in the pant hoots of immature chimpanzees (Pan troglodytes schweinfurthii) of the Budongo Forest, Uganda. Furthermore, I investigate audience effects on pant hoot sequences used during displays to determine the extent to which these vocal structures are flexibly modulated depending on the social environment. Pant hoots are a multi-phase vocal sequence typically used to maintain contact and coordinate movements between individuals and groups over long distances. The question of how this complex and flexible vocal signal develops is key for a better understanding of how chimpanzees navigate dynamic social interactions in fission-fusion societies from both an ontogenetic and a comparative perspective. Results from my thesis show that chimpanzees produced rudimentary pant hoot sequences since birth, suggesting that vocal repertoires are largely innate. However, these sequences presented some structural and acoustic differences when compared to those of older individuals, suggesting they also undergo ontogenetic changes. In addition, the vocal usage and responses to pant hoots in immature chimpanzees was enhanced by greater vocal and social exposure to key group members, such as the mother and adult males, when compared to the development of less gregarious immature individuals. Finally, social context modulated the use of pant hoot phases during vocal displays, likely enhancing the communicative capacities of a species with limited vocal production learning and relatively small vocal repertoire. Taken together, findings from my thesis suggest that the ontogeny of complex chimpanzee vocalisations is socially mediated and that chimpanzee vocal communication is flexibly adjusted depending on the social environment.
Vocal greeting behaviour in wild chimpanzee females
Chimpanzees, Pan troglodytes, are unusual among primates in that they express their social position with a unique vocal signal, the pant-grunt. The call is only produced when encountering a higher-ranking group member and has thus been interpreted as a ‘greeting’ signal. We monitored the calling behaviour of nine adult females in a group of free-ranging chimpanzees, the Sonso community of Budongo Forest, Uganda, when encountering higher-ranking adult males. We found that call production was by no means rigid, but that calls were given only if certain social conditions were met. Although all adult males received pant-grunts from females, the alpha male received a significantly larger proportion of calls. The number of pant-grunts given to males was not correlated with their hierarchical position or with the level of anticipated aggression. Instead, females were significantly more likely to vocalize to other males if the alpha male was absent, suggesting that their calling behaviour was moderated by social inhibition. The presence of the alpha female had a similar yet weaker inhibitory effect. Social inhibition was further increased with increasing numbers of bystanders, especially males. Our results thus demonstrate that chimpanzees use their ‘greeting’ signals flexibly by taking into account the social fabric of their community.
Male blue monkeys alarm call in response to danger experienced by others
Male blue monkeys (Cercopithecus mitis stuhlmanni) of Budongo Forest, Uganda, produce two acoustically distinct alarm calls: hacks to crowned eagles (Stephanoaetus coronatus) and pyows to leopards (Panthera pardus) and a range of other disturbances. In playback experiments, males responded to leopard growls exclusively with a series of pyows and to eagle shrieks predominantly with hacks. Responses to playbacks of these alarm call series matched the responses to the corresponding predators, suggesting that the calls conveyed something about the nature of the threat. When responding to a series of hacks, indicating an eagle, males responded predominately with hacks, but produced significantly more calls if their group members were close to the playback stimulus than far away, regardless of their own position. When responding to a series of pyows, indicating a range of disturbances, males responded with pyows, but call rates were independent of the distance of other group members. The results suggest that males took into account the degree of danger experienced by other group members.
Chimpanzees modify recruitment screams as a function of audience composition
Wild chimpanzees produce acoustically distinct scream vocalizations depending on their social role during agonistic interactions with other group members. Here, we show that victims during such agonistic interactions alter the acoustic structure of their screams depending on the severity of aggression experienced, providing nearby listeners with important cues about the nature of the attack. However, we also found that victims of severe attacks produced screams that significantly exaggerated the true level of aggression experienced, but they did so only if there was at least one listener in the audience who matched or surpassed the aggressor in rank. Our results are consistent with the more general hypothesis that chimpanzees possess sophisticated understanding of third-party relationships, so-called triadic awareness, and that this knowledge influences their vocal production.