Most birds sleep at night.

Larry Lamsa

Birds can seem to be everywhere during the day, flitting among trees, foraging on the ground, visiting feeders and perching on every available stick, post or wire. But where do all these birds go at night?

Diurnal and Nocturnal Birds

Most birds are diurnal, which means they are most active during the day but they typically rest at night. Nocturnal birds, such as owls, frogmouths, nighthawks and night-herons, on the other hand, are most active during the night when they forage, hunt, care for their young, preen and do other activities necessary for survival.

Passerines, waterfowl, shorebirds, gulls and most raptors are all diurnal birds, but when they're not being active, what do they do?

How Birds Sleep

Like other animals that are active during the day, the principle nighttime activity of birds is sleeping. Birds choose how they sleep very carefully to ensure they can survive through the night, and they have certain tricks that help give them warning about predators or to protect them from the elements.

Sleeping away from predators...

• Many bird species choose cavities or niches to roost in at night, which prevents predators from having easy access to them. These same cavities also provide shelter from poor weather, and may include bird roost boxes or empty bird houses.
• Wading birds such as herons, egrets and flamingos will sleep standing in water. The sound and vibrations of a predator coming toward them through the water acts as an instant warning system in case of danger.
• Ducks, geese and other waterfowl will float on the water to sleep, which gives them the same noise alarm system that wading birds take advantage of.
• Small birds sleep perched high in trees, typically close to the trunk of the tree. The trunk holds heat from the daytime to provide better shelter, and the birds will be alerted to any vibrations predators make if they climb the tree looking for prey.
• Many birds, such as red-winged blackbirds and other gregarious species, form large roost flocks at night. This provides them safety in numbers as they sleep, and several birds on the edges of the flock may remain alert through the night to guard against predators or other threats.

From the website, About.com birding/wild birds.