Urbanization Modifies Birds' Acoustic Circadian Timing and Characteristics

Urban-dwelling organisms face significant challenges, and understanding how species adapt to novel urban environments is critical for conservation planning. In this study, we collected avian vocalization data from 220 sites across varying urbanization gradients in China using autonomous recording units SM4 to investigate how urbanization affects the circadian timing and characteristics of bird vocalizations. We found that all 60 bird species in highly urbanized areas advanced their dawn singing by an average of 23.89 min. Although not statistically significant, the dusk singing time was delayed by an average of 6.56 min. Urban-adapted species showed greater shifts compared to urban-sensitive taxa like woodpeckers. Additionally, by analyzing the acoustic characteristics of 3371 vocalizations from three widely distributed bird species, we investigated how avian acoustic traits vary along urbanization gradients. We found that the Asian tit (Parus cinereus) reduced its maximum frequency in highly urbanized areas. In contrast, the light-vented bulbul (Pycnonotus sinensis) and Eurasian tree sparrow (Passer montanus) adapted to the novel urban environment by increasing their minimum frequency and adjusting song structure. While such adjustments in singing timing and acoustic features may improve signal transmission efficiency, the ecological consequences-particularly in terms of immediate and ultimate fitness-remain largely unknown.