title: The relationship between testosterone and long-distance calling in wild male chimpanzees.
abstract: Long-distance calling is a common behaviour in animals that has various important social functions. At a physiological level, calling is often mediated by gonadal hormones such as testosterone (T), particularly when its function is linked to intra-sexual competition for mates or territory. T also plays an important role in the development of vocal characteristics associated with dominance in humans. However, the few available studies of T and vocal behaviour in non-human primates suggest that in primates T has less influence on call production than in other animals. We tested this hypothesis by studying the relationship between T concentrations and pant hooting in wild male chimpanzees (Pan troglodytes schweinfurthii) of the Kanyawara community in the Kibale National Park, Uganda. We found three kinds of correlation. Hourly T averages were positively associated with hourly rates of pant-hooting. Monthly T levels were likewise correlated with monthly rates of pant hooting after controlling for other influences such as fission-fusion rates. Finally, males with high T levels had higher peak frequency at the start of the call climax. These results suggest that T affects the production of pant-hoots in chimpanzees. This implies that the pant-hoot call plays a role in male-male competition. We propose that even in cognitively sophisticated species, endocrine mechanisms can contribute to regulating vocal production.
authors.affiliation: Institute of Biology, University of Neuchâtel, Switzerland.
authors.forename: Pawel
authors.initials: P
authors.lastname: Fedurek
authors.affiliation: Department of Psychology, University of York, UK.
authors.forename: Katie E
authors.initials: KE
authors.lastname: Slocombe
authors.affiliation: Department of Anthropology, University of New Mexico.
authors.forename: Drew K
authors.initials: DK
authors.lastname: Enigk
authors.affiliation: Department of Anthropology, University of New Mexico.
authors.forename: Melissa
authors.initials: M
authors.lastname: Emery Thompson
authors.affiliation: Department of Human Evolutionary Biology, Harvard University.
authors.forename: Richard W
authors.initials: RW
authors.lastname: Wrangham
authors.affiliation: Department of Anthropology, University of New Mexico.
authors.forename: Martin N
authors.initials: MN
authors.lastname: Muller
keywords: acoustic structure; chimpanzee; pant hooting; testosterone; vocal behaviour