Loud calls in male crested macaques, Macaca nigra: a signal of dominance in a tolerant species

Compared to other mammals, sexual signals occur particularly often within the primate order. Nevertheless, little is known so far about the pressures under which these signals evolved. We studied loud calls in wild crested macaques to examine whether these are used as a sexual signal, particularly as a signal of dominance, in this species. Since the structure of loud calls may be influenced by the context in which they are uttered, we tested for contextual differences in call structure. Only males uttered loud calls and analysis of 194 loud calls given by 15 males showed that call structure encoded the caller's identity as well as his social status. Dominance rank was also reflected in the frequency with which males called with alpha males calling most often. The structure of loud calls, however, was not influenced by context. Our findings consolidate the assumption that, in crested macaques, loud calls serve as a signal of dominance, most probably used to prevent contests between males for mates. We herewith provide the first direct evidence for a signal of dominance in a tolerant primate species and discuss why this signal occurs in only one sex.