Song adjustments by an open habitat bird to anthropogenic noise, urban structure, and vegetation

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Urban environments challenge animals with 2 novel impediments to communication: low-frequency anthropogenic noise, which masks vocalizations, and large sound-reflecting structures, which contribute to reverberation. We studied spectral and temporal traits of trill songs of chipping sparrows (Spizella passerina), a species historically found in open grassland habitat, to understand how noise, urban structure, and vegetation affected song traits. On the basis of the song features, males clustered into 2 groups. Males with songs that had lower minimum frequencies and broader bandwidths increased minimum frequency and decreased bandwidths with increasing noise, urban structure, and vegetation. Males with songs that had higher minimum frequencies and narrower bandwidths decreased minimum frequency and increased bandwidth with increasing vegetation but made no adjustments to noise or urban structure. To maintain high vocal performance of trill songs, males should increase trill rates to compensate for decreases in bandwidth, but they did not change this trait. As a result, vocal performance declined across all males with increasing noise and urban structure. Finally, peak frequency decreased with increasing urban structure, suggesting males put more energy into lower frequencies of their songs, possibly to improve sound transmission in human-built environments. Overall, both noise and structure influenced spectral features of songs with limited effects of song timing. Sound reflections from urban structures may have a strong, and underappreciated, influence on animal communication, which may compound the challenges of singing in noise.

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