Urbanization-related vocal variation in passerines: a comparative study

Urbanization is one of the main concerns for biodiversity without fully explored consequences. Avian vocalization was repeatedly found to be altered by urbanization intensity, but the species and song characteristics involved and the mechanisms are unclear. We investigated among- and within-species vocal differences associated with urbanization in 65 European passerines using a phylogenetic comparative approach, considering the sociality, migration status and vocalization complexity of the species, as well as their frequency of occurrence in cities. Dominant frequency range was wider in more urbanized localities across species, but dominant frequency showed urbanization-related differences only in some species. The investigated species-specific traits were not related to the urbanization-related differences in the song traits, and occurrence in cities was not associated with these differences or with the average song characteristics of the species. Therefore, our results suggest that urbanization does not have a general effect on song frequency and that vocalization did not hamper the urban occurrence of birds. However, the consequences of change (or the lack of change) in song in noisy urban environments for individual fitness and on the population level should be explored further, and appropriate measures should preserve suitable habitats for birds in urbanized areas to support diverse bird communities.