Birds have a special technique to keep flying and looking out for predators while migrating at night. It is called unihemispheric slow-wave sleep. Unihemispheric sleep means that ONLY one hemisphere of the brain sleeps while the other is active. There are two hemispheres (halves) of a brain: right and left! One half of their brain rests while the other half makes the bird flap it’s wings and is on the lookout for predators. During their long seasonal migrations, birds have to stay away from predators and have to keep flying, so they developed this special technique! This is how only a half of a bird’s brain is asleep!