The question whether signals provide honest information about an individual lies at the core of many studies addressing the evolution of communicative processes. Copulation calls, for instance, appear to be sexually selected traits, but their regulation and adaptive significance remain poorly understood. The present aim is to identify the information content of copulation calls of female Barbary macaques (Macaca sylvanus), and to examine whether they reliably indicate the timing of ovulation and can be viewed as part of a reproductive strategy influence mating outcome. The study will be performed on free-ranging animals living in Gibraltar and will combine detailed acoustic analysis of the structural and temporal features of the calls with a documentation of the hormonal profile during the ovarian cycle. Hormonal status is determined non-invasively from oestrogen and progestin metabolite measurement in faeces. Once the crucial acoustic features that vary with the hormonal profile have been identified, a series of playback experiments will test whether the information encoded in the calls is salient to listeners. Simultaneously, we will examine whether female reproductive state (and associated variables such as sexual swelling and behaviour) influence males’ responses to the playbacks of different call variants. The results of this study will contribute to a better understanding of the selective pressures and constraints operating on the evolution of sexually selected signals.
