Chimpanzee quiet hoo variants differ according to context
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In comparative studies of evolution of communication, the function and use of animal quiet calls have typically been understudied, despite that these signals are presumably under selection like other vocalisations, such as alarm calls. Here, we examine vocal diversification of chimpanzee quiet ‘hoos’ produced in three contexts - travel, rest and alert - and potential pressures promoting diversification. Previous playback and observational studies have suggested that the overarching function of chimpanzee hoos is to stay in contact with others, particularly bond partners. We conducted an acoustic analysis of hoos using audio-recordings from wild chimpanzees (Pan troglodytes schweinfurthii) of Budongo Forest, Uganda. We identified three acoustically distinguishable, context-specific hoo variants. Each call variant requires specific responses from receivers to avoid breaking up the social unit. We propose that callers may achieve coordination by using acoustically distinguishable calls, advertising their own behavioural intentions. We conclude that natural selection has acted towards acoustically diversifying an inconspicuous, quiet vocalisation, the chimpanzee hoo. This evolutionary process may have been favoured by the fact that signallers and recipients share the same goal, to maintain social cohesion, particularly amongst those who regularly cooperate, suggesting that vocal diversification has been favoured by the demands of cooperative activities.
Crockford , C , Gruber , T & Zuberbuhler , K 2018 , ' Chimpanzee quiet hoo variants differ according to context ' , Royal Society Open Science , vol. 5 , 172066 . https://doi.org/10.1098/rsos.172066
Royal Society Open Science
© 2018 The Authors. Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited.
DescriptionThe study was funded by the Leverhulme Trust, the British Academy, the Leakey Foundation, the European Union’s Horizon 2020 research and innovation programme under grant agreement No. 679787, the Max Planck Society and the Swiss National Science Foundation (grants P300PA_164678, CR13I1_162720 and 31003A_166458). We thank the Royal Zoological Society of Scotland for providing core support for the Budongo Conservation Field Station.
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