Birds sleep in various ways depending on their species, environment, and needs, but generally, they find a safe perch or spot to rest at night. Most birds are diurnal, meaning they are active during the day and sleep at night. They typically perch on branches or other secure places, fluffing out their down feathers to trap heat, tucking their head back and beak into their feathers, and pulling one leg up to their body to conserve warmth. This posture may look uncomfortable but actually keeps them warm and protected from the cold
. Birds have a special mechanism in their legs that tightens their tendons when they perch, allowing them to grip branches firmly and avoid falling while asleep
. Some birds, like waterfowl, sleep standing on one leg near water, and others, like chimney swifts, can even rest while clinging to vertical surfaces
. Birds do not always sleep continuously like humans. They often sleep in short intervals and remain alert to predators or environmental threats. Many birds can engage in unihemispheric slow-wave sleep (USWS), where one half of the brain sleeps while the other half stays awake. This adaptation allows them to rest while remaining vigilant and even to sleep during flight, as seen in species like the Alpine Swift and great frigatebirds, which can sleep with one or both brain hemispheres while flying for extended periods
. In colder seasons or during storms, some birds form roosting groups in sheltered places such as tree hollows or nest boxes to keep warm and safe
. Nesting boxes provide important shelter in winter and are often used by birds for sleeping as well as breeding
. In summary, birds sleep by perching securely, using body postures that conserve heat, and employing unique brain sleep patterns to stay alert and safe, sometimes even sleeping on the wing during long flights
