Background noise but not urbanization level impacted song frequencies in an urban songbird in the Pearl River Delta, Southern China

Rapid urbanization has profoundly transformed habitats and increased noise pollution in urban environments. Elevated noise levels may mask acoustic signals of urban-dwelling organisms such as birds. Singing at higher frequencies is one of typical responses to avoid this masking effect. However, high-frequency signals experience larger attenuation when transmitting in open urban environments. Here, we tested how elevated noise and urbanization affect frequency characteristics and song complexity in the Oriental Magpie-robin (Copsychus saularis), a common urban songbird in tropical Asia. Song recording was conducted in seven cities in the Pearl River Delta, southern China, a highly developed region with rapid pace of urbanization. Our results showed that Magpie-robins sang with higher minimum and maximum frequencies in noisier areas. Neither noise level nor urbanization level impacted other song features, including song length, syllable rate, number of syllables, number of unique syllable types, and syllable transitions in songs. Furthermore, noise level did not affect the choice of song post sites. Our results imply elevated noise levels could induce spectral but not temporal and structural modifications. Taken together, our study adds to a growing number of publications illustrating how phenotypes of birdsongs have been changed in anthropogenic soundscapes.