Function and repeatability of conspicuous and rare vocal signals

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Communication plays a vital role in mediating the social and mating behaviour of animals. Most of our understanding of the ecology and evolution of vocal communication in birds comes from studies of daytime singing behaviour of male songbirds. However, species that are diurnally active often sing intensely just before the sun rises each day in an impressive display known as the dawn chorus. A number of daytime singing species also sing at night. Additionally, females of many songbird species sing, though this behaviour has not been well studied in most species. The social (e.g. territory boundaries, relative quality of neighbours) and environmental (e.g. weather, ambient light, noise) factors that result in the dawn chorus, nocturnal singing, and female song are not well understood. However, these displays likely play at least equally important roles as daytime signalling does in determining fitness (through their contributions to determining reproductive success). The studies that my students and I have designed test hypotheses for why birds sing in these contexts. We use a combined observational and experimental approaches to assess the factors influencing vocal displays in two songbird species: white-throated sparrows and ovenbirds. We focus on singing in the context of communication networks (where many individuals are communicating simultaneously). To do so, we use powerful new recording and song playback techniques to record entire neighbourhoods of territorial birds. This allows us to examine how the social environment and abiotic factors influence displays simultaneously. Using this approach, we can also assess how repeatable these vocal displays are, which is important for understanding how birds might use them to assess mates and rivals. The more consistently produced a vocal display is, the better it can convey information about individual quality. By analyzing vocal behaviours in this way, we can provide new insights into animal communication. It is essential to understand how animals communicate and how different displays influence fitness in natural systems, particularly with accelerating environmental change (e.g. climate, increases in noise and light pollution from human development) that can influence social behaviours of animals, including vocal displays.