Wild chimpanzees (Pan troglodytes schweinfurthii) distinguish between different scream types: evidence from a playback study
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When experiencing aggression from group members, chimpanzees commonly produce screams. These agonistic screams are graded signals and vary acoustically as a function of the severity of aggression the caller is facing. We conducted a series of field playback experiments with a community of wild chimpanzees in the Budongo Forest, Uganda, to determine whether individuals could meaningfully distinguish between screams given in different agonistic contexts. We compared six subjects’ responses to screams given in response to severe and mild aggression. Subjects consistently discriminated between the two scream types. To address the possibility that the response differences were driven directly by the screams’ peripheral acoustic features, rather than any attached social meaning, we also tested the subjects’ responses to tantrum screams. These screams are given by individuals that experienced social frustration, but no physical threat, yet acoustically they are very similar to screams of victims of severe aggression. We found chimpanzees looked longer at severe victim screams than either mild victim screams or tantrum screams. Our results indicate that chimpanzees attend to the informational content of screams and are able to distinguish between different scream variants, which form part of a graded continuum.
KeywordsVocalisations Playback experiment Chimpanzees Screams Social cognition
We thank the staff of the Budongo Conservation Field Station (BCFS), particularly field assistants Monday Gideon, Afeku Alfred, Jackson Okuti, Steven Amati, Sam Adieu, Geresomu Muhamuza and James Kakura for invaluable contributions to running these experiments. We thank Zanna Clay, Tanja Kaller, Anne Marijke Schel and Marion Laporte for assistance with conducting these experiments. We thank Robert Seyfarth, Richard Byrne, Lucy Bates, Drew Rendall and Sarah Papworth for comments on the manuscript. We are grateful to UWA, UNSCT and the Presidents Office for permission to live and work in Uganda. This work complies with the research regulations, ethical guidelines, and laws of Uganda and the guidelines of the University of St Andrews. We thank the Royal Zoological Society of Scotland for providing core funding to BCFS. This research was funded by the BBSRC.
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