Do birds sleep?

One of the many remarkable characteristics of birds is their sleep cycle. Yes, birds sleep, but not in the same way that mammals do. The cycles of Non-rapid Eye Movement sleep and Rapid Eye Movement sleep are shared by birds and mammals, although there are distinctions. The primary distinction is that both cycles are shorter; non-rapid eye movement sleep lasts around two and a half minutes, whereas rapid eye movement sleep lasts approximately nine seconds.

Birds sleep with one-half of their brain awake as well! It's known as unihemispheric slow-wave sleep, and it keeps birds vigilant to prospective predators while yet allowing them to sleep. Other creatures sleep in similar manner, but only birds can manage it. A sleeping bird may vary how much of its brain is asleep by adjusting the width of its eye. Another distinction in a bird's sleep cycle is that it does not lose much muscular tone when sleeping. It makes no difference whether the bird stands, perches, roosts, lies down on the ground, swims, or hangs upside down.