Does the reaction of nocturnally migrating songbirds to the local light source depend on backlighting of the sky

Many avian species prefer to migrate at night (Alerstam 2009, 2011). For tens of thousands of years the only light sources during the dark period of the night were the polarized sunlight, the Moon and stars. However, in the recent decades, due to extensive industrial and urban development, many migrating birds encounter during their nocturnal flights vast areas of bright artificial lights, often including tall structures. Numerous evidences is available showing that anthropogenic lights may attract and disorient birds, sometimes causing their mass mortality (Avery et al. 1980; Verheijen 1985; Evans Ogden 1996; Gauthreaux & Belser 2006; Loss et al. 2012; Longcore et al. 2013). Increasing number and size of the cities, numbers of streetlights, heights of office buildings and the number of offices with lights often lit on after dark make the study of response of nocturnally migrating birds to artificial light sources rather relevant. AVIAN ECOLOGY AND BEHAVIOUR