For the Birds Radio Program: Sleep
What do we know about sleeping birds? They’re not talking.
(Recording of a Barred Owl)
As the mother of three small children, I can personally vouch that one of the most precious commodities in the world is sleep. Which brings us to the obvious question, “How do birds sleep?” This time of year our Northland birds spend over half their lives sleeping or resting, and yet not much is really known about their sleeping habits. Ornithologists do know that active birds tend to sleep more soundly than sedentary ones, but even the most active birds sleep lightly enough to waken at the approach of danger. Most birds I have cared for in my home have their eyes open when I check on them in the night, and many times I’ve heard soft songs in the woods at night—the birds are perhaps aroused by my movements, or maybe just talking in their sleep. The light sleeping habits of geese are credited with saving ancient Rome from a sneak attack during the Fourth Century B.C., and even today geese are used to guard at least one distillery in Scotland.
Birds don’t sleep in beds–well intentioned people often try to make a soft little nest for pet birds, but just about all adult songbirds prefer sitting on a branch. The flexor tendons of their feet shut tight when the leg is bent, locking the foot into position for the night. The few roosting birds I have found perching were tight against the trunk of a tree, where owls and other nocturnal predators were least likely to notice their silhouettes. Chickadees, nuthatches, and bluebirds prefer sleeping in a woodpecker hole or other cavity, especially in winter. Shorebirds usually sleep on shore resting on one foot. Ducks, loons, geese, and other swimmers often rock to sleep in their natural waterbed. There is some circumstantial evidence that swifts and oceanic birds called Sooty Terns sleep on the wing, but many ornithologists argue that this is impossible.
Birds come with a built-in down pillow, and most adult birds rest their sleepy head on their back or wing. Large flightless birds like ostriches and rheas sleep with their head and neck outstretched on the ground, and many baby birds lay their head on the side of the nest.
When evenings are warm, birds sleep with smoothed feathers, but when nights are cold they fluff out their down comforters.
During sleep, a bird’s eyelids usually blink slowly. Two Wisconsin ornithologists studying Barred Owls concluded that they are truly asleep only when their eyelids are fully closed—when the lids are partly closed, the birds are merely dozing. Herring Gulls apparently don’t keep their eyelids shut for more than 60 seconds at a time, but in this species there appears to be a difference in the quality of sleep depending on whether they tuck their bills under their shoulder feathers or face forward. Birds also seem to sleep more soundly when they are sitting than when they are standing. Arctic and Antarctic birds often spend the entire summer daylight period awake, which means that they don’t get much sleep all season.
Avian sleep habits are hard to study because birds awaken so easily when observed, and so nobody has the foggiest idea what the answer is to the ultimate sleep question: do birds dream? You’ll have to ask the birds themselves that question.
(Recording of a Barred Owl)
This is Laura Erickson, and this program has been “For the Birds.”