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.

Keywords: acoustic structure; chimpanzee; pant hooting; testosterone; vocal behaviour.

Fig. 1

A spectrogram showing the four phases of a pant hoot. a = introduction, b = build-up, c = climax, d = let-down (from Fedurek et al. 2013b)

Fig. 2

Mean monthly pant hoot rates and testosterone levels

Fig. 3

Mean monthly pant hoot rates and fission-fusion rates with males

Fig. 4

Mean hourly levels of pant hoot rates and testosterone levels

Fig. 5

The relationship between mean annual levels of testosterone and mean peak frequencies at the start of the climax