When Birds Change the Soundscape: Distraction and Appraisal in Urban Parks

Birdsong can alter the perception of an urban soundscape; however, its acoustic effects are not fully described by conventional sound level measures. The presence of singing birds introduces additional acoustic components that can influence the overall character and experience of an urban environment. This study examines bird-enriched urban soundscapes using the Total Distraction Coefficient (TDC), an objective acoustic parameter based on loudness, loudness growth rate, and sharpness, which was developed to estimate how strongly sudden and unexpected loudness changes disrupt concentration. Five park soundscapes containing different singing bird vocalizations were analyzed and compared with the same park background without birds. Compared with this background (TDC = 0.303), the addition of birdsong did not increase the TDC calculated with the original model. Instead, the TDC decreased to 0.242–0.267, mainly because the birdsong raised the mean loudness, so that the loudness peaks of the background stood out less. Sharpness, on the other hand, differed clearly between the soundscapes and increased with the peak frequency of the bird vocalizations. Furthermore, the acoustic character of the same urban environment changed depending on which bird species was added. These findings are compared with the listeners’ ratings of the same soundscapes on bipolar adjective pairs, obtained in a previous study, which describe features such as pleasantness, naturalness, diversity, and soothing quality. In an exploratory comparison of the five soundscapes, TDC did not follow listeners’ appraisal, suggesting that birdsong can change how an urban soundscape is perceived without increasing its distraction potential as estimated by TDC.