Résultat de la recherche
The Function of Chimpanzee 'Waa' Barking in Agonistic Contexts
Chimpanzees communicate to two different audiences during aggressive interactions
Conflict and aggressive interactions are common phenomena in group-living animals and vocal behaviour often plays an important role in determining their outcomes. In some species, vocal signals seem to provide bystanders with information about the nature of an ongoing aggressive interaction, which can be beneficial for the victims. For example, in chimpanzees and some other primates, victims adjust their screams depending on the composition of the by-standing audience, probably to solicit their support. Considerably less is known, however, about the role of other call types produced by victims of aggression. In this study, we focused on the fact that, immediately after screams, chimpanzee, Pan troglodytes schweinfurthii, victims often produce 'waa' barks, but little is known about their function. Our results showed that for screams, but not 'waa' barks, production was dependent on the audience composition with victims being more likely to scream when adult or late-adolescent males were in close proximity. We also found that after 'waa' barking, but not screaming, victims were more likely to retaliate against and less likely to reconcile with their aggressors, and that 'waa' barking was more common after victims had received support from other party members. These results suggest that, in chimpanzees, victims of aggression vocalize with a dual social strategy of attempting to recruit support from bystanders and to repel their attackers by signalling readiness to retaliate. We conclude that victim scream and 'waa' bark calls, although often produced during the same agonistic event, are directed at different audiences and fulfil different social functions, and that these calls can mediate both aggressive interactions and aggressor-victim relationships following aggression. (C) 2015 The Association for the Study of Animal Behaviour. Published by Elsevier Ltd. All rights reserved.
Chimpanzee lip-smacking facilitates cooperative behaviour
Signalling plays an important role in facilitating and maintaining affiliative or cooperative interactions in social animals. Social grooming in primates is an example of an interaction that requires coordination between partners but little is known about communicative behaviours facilitating this activity. In this study, we analysed the communication of wild chimpanzees of Budongo Forest, Uganda, as they entered and maintained a naturally occurring cooperative interaction: social grooming. We found that lip-smacking, a distinct multimodal oral gesture produced during grooming, coordinated this activity. Lip-smacking at the beginning of grooming bouts was significantly more often followed by longer and reciprocated bouts than silent grooming initiations. Lip-smacks were more likely to be produced when the risk of termination of the interaction by the recipient was high, for instance when grooming vulnerable body parts. Groomers were also more likely to produce lip-smacks during face-to-face grooming where the visual aspect of the signal could be perceived. Data are consistent with the hypothesis that chimpanzee lip-smacks function to coordinate and prolong social grooming, suggesting that this oral signal is an example of a communicative behaviour facilitating cooperative behaviour in chimpanzees.