It's all in the toes for wall-hanging bird
I have noticed a strange bird behavior I've never seen before. A large, gray bird has started roosting at night in the corner of the stucco wall on my back patio. He is just hanging by his toes, I assume. Is this common? I have bird-watched for many years now and have never noted this behavior. We have lived here 13 years. What's up? How can he sleep and not fall off the wall?
— Jean B., Eagle Point
Jean, without more detail, the ornithology geeks here at the Since You Asked Institute of Feathered Sciences don't know what species of bird you're looking at as it settles down for its nightly snooze. But they do know a thing or two about sleeping birds and why they don't fall down.
Sleep is serious business for birds, often involving a sheltered spot like your patio, which may be out of the reach of likely predators. The feet of passerines (birds with three forward-pointing toes and one rear-pointing toe, such as sparrows, wrens and warblers) are adapted for grasping a perch.
And when a passerine lands, two tendons called flexors, which are attached to the bird's toes, automatically tighten, locking the bird's toes around the perch. It's an involuntary reflex that involves the bird's weight keeping the leg in the locking position, so the bird doesn't have to be awake and thinking about gripping with its toes.
You may notice that the roosting bird's belly feathers tend to cover its feet. In cold weather it may even squat down to better cover its feet, which also helps the toe-gripping reflex. The tendons won't release until the bird straightens out its legs, as it will when it flies off. The whole thing is just another amazing adaptation in the tool kits of our feathered friends.
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