Do beak volume and bite force influence the song structure of sympatric species of seedeaters (Thraupidae: Sporophila)?

ABSTRACTSong structure can be constrained by morphological characters such as beak size. Studies have shown that songbirds with larger beaks produce songs with a lower frequency, narrower frequency range and lower note rates than birds with smaller beaks. We tested whether beak volume and bite force constrain song parameters in three Neotropical seedeaters that show a gradient of beak size and force (Sporophila beltoni, S. caerulescens and S. hypoxantha). We also determined the relationship between body size and song structure. We evaluated the song structure of these species, measuring differences that may help them to segregate the acoustic space, since they occur in sympatry. These birds can be predicted to segregate the acoustic space to reduce overlapping of their songs, which is a possible result of the force of sexual selection. Individuals of each species had their beaks and bite forces measured and their own territorial songs recorded in the field. Only S. caerulescens showed a positive relations...