Artificial night lighting rather than traffic noise affects the daily timing of dawn and dusk singing in common European songbirds

It is well established that artificial night lighting can influence animal orientation, but there is less information about its effects on other behaviors. Previous work suggested that light pollution can affect both seasonal and daily patterns of behavior. The aim of our study was to investigate the effects of artificial night lighting and daytime traffic noise on the timing of dawn and dusk singing in 6 common songbirds. We recorded singing behavior in 11 nonurban plots: 2 plots with light, but no noise, 3 with light and noise pollution, 3 with noise, but no light, and 3 undisturbed forests. Our results show that artificial night lighting, but not noise, leads to an earlier start of dawn singing in 5 out of 6 species, ranging on average from 10min for the song thrush to 20min for the robin and the great tit. This effect was strongest at higher light intensities. We further show that dusk song is also affected: 3 species continued dusk singing for longer in lighted areas, but the effect was smaller than that observed for dawn song (from about 8min for the blackbird to 14min for the great tit). For all species, onset and cessation of singing changed relative to sunrise and sunset with the progress of the season. Rain delayed the onset of singing at dawn and advanced the cessation at dusk. We discuss the implications of our findings in the context of sexual selection