Do passerine birds utilise artificial light to prolong their diurnal activity during winter at northern latitudes?

Abstract

Boreal regions with a mild winter climate, such as the western coastal area of Norway, may hold a number of wintering passerine birds, in spite of the short day length in mid winter. To determine whether birds wintering under such conditions were able to use artificial light to increase their activity periods, day-time and night-time bird censuses were done from October to March in a residential area in Bergen, western Norway, along roads lit by street lights. Situated at latitude 60°N, the area has 18 hours of darkness in mid winter. Twenty-four passerine species were recorded. Of these European Robin Erithacus rubecula, Common Blackbird Turdus merula, and Eurasian Wren Troglodytes troglodytes regularly started their activity several hours before sunrise, whereas Great Tits Parus major and Blue Tits Cyanistes caeruleus did so to some extent. The other species did not start their activity until morning civil twilight. Measurements of distance from street lights for European Robins during night-time showed that the birds were closer than random to lights. The study shows that some passerine species are able to extend their activity period by 4–5 hours utilising artificial light during the darkest part of the winter.