Are bird species that vocalize at higher frequencies preadapted to inhabit noisy urban areas?

Urban environments have become an increasingly important part of the world's ecosystems, and the characteristics that enable animals to live there are not fully understood. A typical urban characteristic is the high level of ambient noise, which presents difficulties for animals that use vocal communication. Urban noise is most intense at lower frequencies, and, therefore, species vocalizing at higher frequencies may be less affected and thus better able to inhabit urban environments. We tested this hypothesis with within-genera comparisons of the vocalization frequency of 529 bird species from 103 genera. We found that species occurring in urban environments generally vocalize at higher dominant frequency than strictly nonurban congeneric species, without differing in body size or in the vegetation density of their natural habitats. In most passerine genera with low-frequency songs, which are more subject to masking by noise, minimum song frequency was also higher for urban species. These results suggest that species using high frequencies are preadapted to inhabit urban environments and that reducing noise pollution in urban areas may contribute to restore more diverse avian communities.