For the Birds Radio Program: How Birds Sleep
(Recast from August 3, 1987) 3:31
(Recording of a American Crow)
One of the most precious commodities for any mother of small children is sleep. Which brings us to the obvious question, “How do birds sleep?” Although most birds spend about a third of their day sleeping or resting, not much is really known about avian sleeping habits. Ornithologists do know that active birds tend to sleep more soundly that sedentary ones. But even the most active birds sleep lightly enough to awaken at sounds of danger. Many times at night in the woods I have heard birds sing a soft song, perhaps aroused by my sounds, or maybe just talking in their sleep. Geese, which are louder than songbirds, are said to have alerted the ancient Romans of a sneak attack in the fourth century B.C., saving Western civilization, and even today geese are used to guard at least one distillery in Scotland because of their light sleep.
Birds may not sleep in beds, but most of them do use a down pillow to rest their head–that is, they turn their head and rest it on their back or wing. Songbirds can perch on branches while in deep sleep–the flexor tendons of their feet shut tight when the leg is bent, locking the foot into position for the night. Many water birds sleep on shore on one foot. Ducks, loons, geese, and other swimmers can sleep like this on land or rocking in their natural waterbed. Many young birds and large flightless birds like the Ostrich and Rhea sleep with their head and neck extended along the ground. Woodpeckers, chickadees, bluebirds, nuthatches, and some other groups of birds sleep in cavities or birdhouses. A few birds will also use old nests for sleeping in, but most land birds sleep in trees or dense weeds. The few roosting birds I have found perching were tight against the trunk of trees, where they seemed least likely to present a noticeable silhouette for owls and other night hunters. In summer, when evenings are warm, birds sleep with smoothed feathers, but in winter they fluff out their down for warmth.
There is some circumstantial evidence that swifts and oceanic birds called Sooty Terns sleep on the wing, but some ornithologists doubt that this is really possible.
During sleep, the eyelids of a bird usually blink slowly. Two ornithologists studying Barred Owls concluded that they sleep when their eyelids remain fully closed, and merely doze when their eyelids are only partly closed. Herring Gulls apparently don’t keep their eyelids all the way shut for more that 60 seconds at a stretch, but there does appear to be a difference in the quality of their sleep depending on whether they tuck their bills under their shoulder feathers or face forward. Birds also seem to sleep more deeply when they are sitting than when they are standing. Birds living in the Arctic or Antarctic summer often spend the entire daylight period awake, which means that they don’t get much sleep all season.
Sleep habits are hard to study in birds because they awaken so easily when they are observed. And nobody has the foggiest idea whether birds actually dream. It’s hard to theorize about what bird dreams might be–their real lives are so fairy like that their fantasy lives are beyond my imagination.
(Recording of a American Crow)