The acoustic structure of chimpanzee pant-hooting facilitates chorusing
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Duetting or chorusing behaviour occurs in a wide variety of animals and is posited to fulfil various important functions including territory defence and social bonding. The structure of calls produced in choruses might be shaped in a way that facilitates such joint vocal displays. In this study, we test the hypothesis that flexibility to modify the temporal structure of chimpanzee pant-hoots, vocalisations often given jointly with other individuals, facilitates chorusing. The results of this study, which was conducted on two communities of wild chimpanzees in Uganda, support this hypothesis. First, the duration of the build-up phase of the pant-hoot correlated with the latency with which the partner joined in the call, suggesting that males prolong the duration of the build-up to allow others to join in the call and to increase the likelihood of a chorus occurring. Second, the loud climax phases were significantly longer when produced in choruses than alone, which suggests that males prolong this part of the call when calling in choruses. Within chorus pant-hoots, there was a positive relationship between the number of climax elements given by two calling partners, suggesting that males adjust the temporal structure of their call to mirror their partner's call. We conclude that the basic acoustic structure of chimpanzee pant-hoots and the flexibility with which males adjust the duration of the constituent phases promote chorusing, and that the temporal structure of this rather stereotyped vocalisation is sensitive to fine details of the vocal responses of the audience.
KeywordsChimpanzees Pant-hoot chorusing Acoustic structure Vocal plasticity
We would like to thank the directors of the Kibale Chimpanzee Project, Richard Wrangham and Martin Muller, for allowing us to conduct this research on the Kanyawara chimpanzees. Thank you to the KCP field manager, Emily Otali, and KCP field assistants, Francis Mugurusi, Solomon Musana, James Kyomuhendo, Wilberforce Tweheyo, Sunday John and Christopher Irumba, who were extremely helpful during the fieldwork. We thank Klaus Zuberbühler for permission to work with the Budongo chimpanzees and the Royal Zoological Society of Scotland for providing core funding for the Budongo Conservation Field Station. We are grateful to Budongo field assistants, Monday Gideon, Jacob Alio, Sam Adue, Jackson Okuti and Robert Eguma, for invaluable assistance with data collection. We also thank Ed Donnellan for assisting with the analysis for this paper. We are grateful to Klaus Zuberbühler, Richard Wrangham, Martin Muller, Geoffrey Hall and Stuart Semple for useful comments on a draft of this manuscript and to the editor David Watts, Robert Seyfarth, and an anonymous reviewer for helpful comments on the manuscript. PF was funded by a BBSRC studentship, a Leakey Foundation General Grant and an American Society of Primatologists General Small Grant. AS and KS were funded by a BBSRC project grant to KS.
Ethical approval for this study was obtained from the Department of Psychology Ethics panel at the University of York and permission to conduct the study was granted by the Ugandan Wildlife Authority and the Ugandan National Council for Science and Technology. The study complied with the current laws of Uganda.
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