Cotinga communication constrained: body size and lekking behaviour influence cotinga song (Aves: Cotingidae)

Bird vocalizations can be influenced by different ecological and evolutionary factors. For example, the 'morphological constraint' hypothesis predicts a negative correlation between body size and song frequency, while the 'acoustic adaptation' hypothesis predicts that organisms in dense habitats sing lower-frequency songs compared with organisms inhabiting more open areas. However, little is known about how song structure is influenced under different lek mating systems. Here, we used 61 cotinga (Aves: Cotingidae) species to investigate fundamental relationships between morphology, ecology and mating system by compiling a dataset on song, morphological and environmental traits as well as different lek mating systems. We found that both peak frequency and frequency range correlate negatively with body size. Moreover, our results suggest a positive (albeit marginally significant) correlation between lek presence and frequency range. Our results thus support the 'morphological constraint' hypothesis, while environmental factors barely influence cotinga songs. These findings suggest that cotinga species are vocally constrained by body size, probably because of the limitation on the sound-producing organs, while evolution might have favoured a broad frequency song in avian lek mating systems.