Song type affects hearing sensitivity in sparrows
The evolution of vocal signals can be constrained by a well-known host of factors including habitat effects on sound propagation, morphology of sound-producing structures and phylogenetic relationships among species. However, we know less about the influence of these constraints on the evolution of hearing. In this paper, we evaluated differences in the sensitivity of the auditory system in 9 species of sparrows to tones of different frequencies. Our experimental design included species from a range of habitats (grassland, shrub and closed canopy), and with a range of song types (relatively pure tone, primarily trilled and complex with multiple syllable types). Surprisingly we found that birds with high frequency sounds in their songs did not have particularly good high frequency hearing, and similarly birds in open habitats (where songs tend to be produced with high frequencies) did not have particularly good high frequency hearing. Neither of these results was predicted nor were they consistent with the literature. Instead, birds with complex songs (i.e. songs with many different elements that span a range of frequencies) have substantially better high-frequency hearing than birds with simpler song types. This is one of the first papers to show that the complexity of the vocal repertoire, and not just the range of frequencies used in that repertoire, has a significant effect on the evolution of hearing. The paper also helps us think about components of a song that might be important in sexual selection.
Alejandro Vélez, Megan D Gall, Jianing Fu, and Jeffrey R Lucas. 2014. Song structure, not high-frequency song content, determines high-frequency auditory sensitivity in nine species of New World sparrows (Passeriformes: Emberizidae). Functional Ecology doi: 10.1111/1365-2435.12352