![]() ![]() In autumn, some vertical reactions were ∼40% more likely to occur at ∼50 m from the lights than at >2.2 km. Reactions in spring were up to ∼60% more likely to occur at ∼35 m from the lights than at >1.5 km. Reactions were up to 40% more likely to occur in autumn than in spring depending on the threshold magnitude of turning angle. Flight paths with and without reactions were generally closer to our experimental site in spring than in autumn when the lights were on. ![]() We identified change points along flight paths where birds turned horizontally or vertically, and we considered these indicative of reactions. We analyzed 1501 high-resolution 3D nocturnal flight paths of free-flying migrants and diurnally captured 758–2009 birds around experimental lights during spring and autumn 2016, and spring 2017. We conducted a controlled longitudinal experiment with light-emitting diode floodlights and considered nearby structures that turn on lights at night. We predicted that birds in flight will react close to low-rise lights, and be attracted and grounded near light sources, with a stronger effect on juveniles during their autumn migration. We hypothesized that common low-rise lights pointing downward also affect the movement of nocturnal migrants. Artificial light at night (ALAN) on tall or upward-pointed lighting installations affects the flight behavior of night-migrating birds. ![]()
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