At the end of April, or when spring starts to thaw, a great migration north begins. Thousands upon thousands of songbirds make the trek, but you won’t see most of them. They fly in the dark to avoid as many predators as possible, and in doing so evade the humans trying to study them as well.
So, even as 4,000 of the world’s 10,000 bird species fly over our heads every night, scientists are still scrambling to answer basic questions. When do birds decide to migrate? How dangerous is it? And how do anthropogenic factors like light pollution and climate change impact birds as they travel?
Read at: Popular Science