Urbanization alters the song propagation of two human-commensal songbird species.

Urban expansion has increased pollution, including both physical (e.g., exhaust, litter) and sensory (e.g., anthropogenic noise) components. Urban avian species tend to increase the frequency and/or amplitude of songs to reduce masking by low-frequency noise. Nevertheless, song propagation to the receiver can also be constrained by the environment. We know relatively little about how this propagation may be altered across species that (1) vary in song complexity and (2) inhabit areas along an urbanization gradient. We investigated differences in song amplitude, attenuation, and active space, or the maximum distance a receiver can detect a signal, in two human-commensal species: the house sparrow (Passer domesticus) and house finch (Haemorhous mexicanus). We described urbanization both discretely and quantitatively to investigate the habitat characteristics most responsible for propagation changes. We found mixed support for our hypothesis of urban-specific degradation of songs. Urban songs propagated with higher amplitude; however, urban song fidelity was species-specific and showed lowered active space for urban house finch songs. Taken together, our results suggest that urban environments may constrain the propagation of vocal signals in species-specific manners. Ultimately, this has implications for the ability of urban birds to communicate with potential mates or kin.