Singing from North to South: latitudinal variation in timing of dawn singing under natural and artificial light conditions

1. Animals breeding at northern latitudes experience drastic changes in daily light conditions during the breeding season with decreasing periods of darkness, whereas those living at lower latitudes are exposed to naturally dark nights throughout the year. Nowadays, many animals are also exposed to artificial night lighting (often referred to as light pollution). 2. Animals strongly rely on variation in light levels to time their daily and seasonal behaviour. Previous work on passerine birds showed that artificial night lighting leads to earlier onset of dawn song. However, these studies were carried out at intermediate latitudes with more limited seasonal changes in daylength, and we still lack an understanding of the impact of artificial night lighting in relation to variation in natural light conditions. 3. We investigated the influence of natural and artificial light conditions on the timing of dawn singing in five common songbird species in each of three regions in Europe that diff...