Non-breeding European robins adjust their song in noisy environments.

Noise pollution is a global threat to biodiversity, significantly affecting acoustic communication in birds and other taxa. While European robins (Erithacus rubecula) adjust their songs in response to urban noise during the breeding season, little is known about song adjustments during the non-breeding season, when song plays a crucial role in survival by helping secure winter territories with adequate resources and shelter. To better understand the effect of noise on avian communication, we investigate whether robins modify their non-breeding song in noisy environments. We analyed the autumn songs of 25 robins exposed to varying background noise levels and found that robins increase the minimum frequency of their songs and extend phrase duration by singing fewer but longer syllables per phrase in noisy environments-adjustments that may mitigate acoustic masking. Our results provide valuable insights into the broader impact of urbanization on bird communication and highlight the need to consider non-breeding vocal behavior in conservation efforts. These findings underscore the year-round impact of noise pollution on birdsong, suggesting it affects various aspects of avian life history. However, it remains unclear whether these adjustments have evolutionary consequences for survival, as changes in key song parameters may affect how rivals interpret signals. Therefore, future studies should explore how vocal plasticity influences winter territory quality, predation rates, and individual survival.