The effect of artificial light and latitude on foraging activity in resident passerines in Northern Europe
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- Master’s theses (MINA) 
Over the last couple of decades, there has been an increasing interest in the ecological consequences of artificial light on wildlife. At northern latitudes, winter is characterized by short days and low temperatures, compared to winter climate at lower latitudes. In these conditions, resident birds need a higher food intake to sustain their metabolism and maintain body temperature. Artificial light may prolong forage opportunities for resident birds during winter. The main objective of this thesis was to investigate if six resident passerine species would utilize artificial light by commence foraging before sunrise and continue after sunset. Further, by conducting a meta-analysis, an objective was to investigate if onset of foraging was correlated with latitude. Two feeding stations, one illuminated and one control, were placed in a forest area in Ås, Norway. A camera was placed in front of each feeding station to record daily activity of the passerines in December and February. In December, the great tit commenced foraging earlier relative to sunrise when artificial light was present, but was not affected by artificial light to continue foraging after sunset. In February, the great tit was not stimulated by artificial light to commence foraging before sunrise, nor continue to forage after sunset. Artificial light did not affect earlier onset of foraging at sunrise in Poecile sp. There was not enough data to do analyses for the other passerine species. Great tit´s onset of foraging was correlated with latitude. At the northernmost location, the great tit commenced foraging several hours before sunrise, compared to the southernmost location, where the great tit commenced foraging only a few minutes before sunrise. The great tit started foraging relatively early despite the absence of daylight at the northernmost location. These results suggest that some resident passerine species may utilize artificial light to prolong their foraging activity during midwinter, and that onset of foraging is limited by daylength at northern latitudes. Further, that early onset of foraging increases with increasing latitude, and that light levels at twilight might be the minimum light level needed for resident birds to commence foraging.