A bird flying at 3 km elevation can easily see lights 100 km away. (Not just skyglow from large cities, but also the lights themselves)
Despite most of the east coast of the US being relatively far from bright skies (as defined by their team), 60% of the east coast is within 100 km of bright skyglow.
Radar data is consistent with the hypothesis that skyglow attracts migrating birds into cities, where they are mortal danger of collisions with (lit) buildings.
-James McLaren #Eurodark
Here's a recent study from a number of members of the same team, "Artificial light at night is a top predictor of bird migration stopover density": https://www.nature.com/articles/s41467-023-43046-z
They find that skyglow is the second most positive predictor of birds migratory direction (elevation was the largest).
Forest and landcover had a much smaller impact than skyglow. #Eurodark
Twice a year, billions of nocturnal avian migrants traverse landscapes that are changing through natural and anthropogenic forces. Here, the authors identify light pollution as an influential predictor of bird migration stopover density across the USA.
Christopher Kyba