Do Birds Sleep in Their Nests? Where Birds Really Sleep

What are nests for?

A bird’s nest is built for one breeding attempt. It keeps eggs together and warm, hides them from predators and gives helpless chicks a safe place to grow. Once the young have fledged, the nest is usually dirty, full of droppings and parasites such as mites and fleas, and easy for predators to find. Most birds simply abandon it.

The American robin, for example, builds a new mud-lined nest for each brood and does not use the old one for sleeping. During the nesting season, the parent incubating or brooding, usually the female, spends the night on the nest. Her partner roosts nearby; in summer, male robins often gather in communal roosts at night.

Where do songbirds sleep?

Most small songbirds choose a roost spot that is sheltered from wind and hidden from owls, cats and other night predators. Common choices are:

• Dense evergreen trees and shrubs, such as spruce, pine, cedar and holly
• Thick hedges, brambles and vine tangles
• Reed beds and tall grass for some marsh birds
• Tree cavities, rock crevices and nest boxes
• Ledges and nooks on buildings

The northern cardinal roosts in dense shrubs, thickets and evergreens, often near its feeding areas. The black-capped chickadee usually sleeps alone in a small cavity, such as an old woodpecker hole or a natural crack in a tree, which keeps it out of the wind on cold winter nights.

Birds that do sleep in nests or holes

There are exceptions to the rule, and they are some of the most interesting sleepers:

• Woodpeckers excavate tree holes and often use them, or extra holes they dig, as night roosts all year.
• Sociable weavers of southern Africa build huge shared nests used by dozens of birds all year, both for breeding and for sleeping.
• House sparrows sometimes build or reuse nests for roosting in cold weather.
• Wrens often pack together into a nest box or old nest on freezing nights to share body heat.
• Eastern bluebirds may roost several to a cavity or nest box in winter.

In these cases, the roost is usually a cavity or a specially built roosting nest rather than the open cup where eggs were laid.

How do birds sleep?

Many birds sleep with their head turned backward and their bill tucked into the feathers of their back, not under the wing, as is often said. They fluff out their feathers to trap a layer of warm air and often draw one leg up into their belly feathers.

Long-legged waders such as flamingos and herons often sleep standing, frequently on one leg, which saves body heat. Find out why in why do flamingos stand on one leg?. Ducks, geese and swans often sleep floating on open water, where land predators cannot reach them.

Sleeping with one eye open

Birds can do something people cannot: sleep with one half of the brain while the other half stays awake. This is called unihemispheric slow-wave sleep, and the eye connected to the awake half stays open.

In a famous experiment published in 1999 in Nature, researchers filmed mallard ducks sleeping in a row. Ducks at the ends of the row kept the eye facing away from the group open far more often than ducks in the middle, and the half of the brain linked to that eye stayed more alert. The birds were effectively keeping watch while resting.

Sleeping in flight

A few birds sleep in the air. In 2016, scientists reported brain recordings from great frigatebirds flying for days over the ocean. The birds slept in the air in brief bursts, often lasting only seconds, sometimes with one half of the brain and sometimes with both. In total they slept less than an hour a day in flight, compared with more than 12 hours a day on land.

Common swifts, which stay airborne for most of the year outside the breeding season, are also thought to sleep on the wing.

Why don’t birds fall off perches?

Perching birds have tendons that run from the muscles of the leg, down behind the ankle joint, to the toes. When a bird crouches on a branch, bending its legs tends to pull these tendons tight and curl the toes around the perch. In many songbirds, tiny ridges on the tendons and their sheaths may help hold the grip with little effort.

Studies suggest this is only part of the story. Sleeping birds also stay balanced through constant small muscle adjustments, much as people can stay upright while dozing in a chair. Together, these allow a sleeping bird to stay on its perch through a windy night.

Surviving cold nights

Long winter nights are a challenge for small birds, which must survive many hours without food. Many store extra fat during the day and burn it overnight to stay warm.

Black-capped chickadees roost in cavities and can lower their body temperature by several degrees at night, a controlled state called regulated hypothermia, which reduces the energy they need. Hummingbirds take this further, entering deep torpor on cold nights. Robins and other birds that do not use cavities gather in sheltered roosts; wintering American robins can form night roosts of thousands of birds, as described in where robins go in winter.

Myths about bird sleep

“Birds sleep in their nests every night.” Only adults with eggs or young chicks do, plus a few species that use cavities or special roosting nests.

“Birds tuck their heads under their wings.” Most actually tuck their bill into the feathers of the back or shoulder.

“Birds never sleep in the air.” Brain recordings show that at least some, such as frigatebirds, really do.