Asleep On The Wing

When birds need sleep, they do it on the fly--quite literally. They're able to enter a special kind of half-sleep state that lets them rest midair, which is especially important if you're a migratory bird, like the Alpine swift, clocking thousands of miles at a time. Glide into the astounding world of avian sleep.

from Videos | Smithsonian Magazine https://www.smithsonianmag.com/videos/category/science/asleep-on-the-wing/
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