The Effects of Anthrophony on Song Traits in European Robins (Erithacus rubecula)

The increasing urbanisation has important impacts on natural soundscapes, through habitat loss and noise pollution (anthrophony), affecting acoustic communication in wildlife. Birds living in cities often adjust their songs to avoid masking by low-frequency traffic noise, but little is still known about how multiple song traits vary during the day. In this study, we investigated how anthrophony affects song traits in European robins (Erithacus rubecula) over a 10-h timeframe by comparing urban and rural populations. We recorded 59 robins in the city of Edinburgh, Scotland, and 54 robins in the Midlothian countryside and compared their songs with linear mixed models. Minimum frequency in rural robins decreased over the day, whereas it remained elevated and constant in urban robins. Urban songs were also longer, less complex and had narrower frequency ranges. These patterns suggest plastic regulation of minimum frequency in response to background noise, anthrophony in urban areas and biophony in rural areas, while suggesting potential constraints on other song traits. Although the fitness consequences of reduced complexity and frequency range remain unclear, behavioural plasticity may help preserve signal reliability in urban habitats.