Artificial light at night causes advanced initiation of dawn song in songbirds in Linköping, Sweden

Abstract: It is known that artificial light at night has a role in disrupting many birds’ routines when it comes to timing of dawn song. However, studies show various results on which species that are affected, how much and on what latitude. Birds at northern latitudes is experiencing longer and brighter natural nights during the breeding season as the spring is progressing, compared to birds living in areas more south. The bright nights might affect how the birds respond to the artificial light at night. This study's aim was to investigate how different species of songbirds in Linköping (58°N), Sweden, time their dawn song during breeding season, depending on presence or absence of artificial light at night coming from street lamps. The results show that early singing species are more affected than late singing species. The common blackbird for example, advanced its song because of artificial light, up to over an hour on average. Late singing birds was also affected by the urban lights, though not as strongly as the early singing species. Also shown was that the temperature and the amount of cloudiness, did not affect the difference in timing of dawn song between the locations. Future studies should focus on collecting data from more northern latitudes. The effect the advanced timing of dawn song, both regarding the birds on an individual scale and also regarding the ecosystems in total,should also be investigated further.