Singing in the city: high song frequencies are no guarantee for urban success in birds

Urbanization involves dramatic environmental alterations, which can limit survival and reproduction of organisms and contribute to loss of biodiversity. One such alteration is anthropogenic noise, which biases natural ambient noise spectra toward low frequencies where it may interfere with acoustic communication among birds. Because vocalizing at higher frequencies could prevent masking by noise, it has been hypothesized that species with higher song frequencies should be less affected by urbanization. Indeed, evidence is accumulating that urban birds often vocalize at higher frequency than nonurban birds. However, the extent to which singing frequency affects their success in cities is less clear. We tested this hypothesis with a comprehensive phylogenetic Bayesian analysis comparing song frequency of songbirds from 5 continents with 4 measures of success in urbanized environments. Tolerance to urbanization was not associated with dominant or minimum song frequencies, regardless of the metric used to quantify urban success and the intensity of the urban alterations. Although song frequency was related to habitat preferences and body size of the species, none of these factors explained the lack of association with urban success. Singing high may be beneficial for signal perception under noisy conditions, but these high frequencies are apparently no guarantee for the success of bird species in urbanized environments.