Nutze die nacht: Amseln (Turdus merula) verlängern ihre nahrungssuche unter künstlichem nachlicht

Abstract

In the urbanized world, the diurnal cycle of light and darkness has lost its accuracy due to artificial light at night (LAN). Because light is one of the most important zeitgebers for the synchronization of the endogenous clock, this loss of the night has serious implications for health and activity patterns. Although it is a well-known phenomenon that LAN advances the onset of dawn song of passerines, little is known ABOUT whether birds extend their activity into the evening hours and THUS may benefit from exploiting the night light niche. By observing wild urban Blackbirds (Turdus merula) under different LAN intensities, we found birds exposed to high levels of LAN to forage longer in the evening than their conspecifics in the darker areas. This difference was most pronounced during the short days in March, but decreased steeply towards the summer solstice. However, body condition of the Blackbirds did not correlate with the exposure to LAN, indicating that urban birds extending their activity under LAN might not benefit from the prolonged foraging times. Our findings further indicate that male Blackbirds are more sensitive to LAN than females. This study reveals that LAN plays a considerable role in the activity times of urban Blackbirds but, regarding their body condition, other urban factors may be more important than the influence of LAN.