This story comes to you through a partnership between Audubon and BirdNote, a show that airs daily on public radio stations nationwide.
[audioplayer:191681|align:left|caption:Asleep on a Perch]
Written by Bob Sundstrom
When birds retire for the night, they seek a place to roost. And while the world of birds includes a variety of sleeping arrangements, many songbirds such as cardinals or finches sleep perched in the safety of dense trees or shrubs.
When such a bird flies into the branches of a tree at nightfall, it perches on a twig and perhaps preens a bit. Then the bird lays its head over its back and tucks its bill into its feathers, while pulling one leg up into its belly feathers. Then it falls asleep, standing on one leg.
On one leg? Why doesn’t it fall over as soon it relaxes into sleep?
Because of an adaptation peculiar to perching birds.
A bird’s weight pressing down on its heel tightens a tendon in the heel, which in turn forces the toes to close in a very tight grip on the twig. As long as the bird holds that pose with its body weight pressing down, its perching grip remains secure, locked in position. Right through the night.
BirdNote is funded by listeners like you. You make shows like this possible. Learn more at birdnote.org. and like us on Facebook. For BirdNote, I’m Michael Stein.
Musical selection “Mountain of the Night” on Inspiration by Lynne Arriale, TCB Music 2001. Bird sounds provided by The Macaulay Library of Natural Sounds at the Cornell Lab of Ornithology, Ithaca, New York. Song of Northern Cardinal  recorded by G.A. Keller; BirdNote’s theme music was composed and played by Nancy Rumbel and John Kessler. Producer: John Kessler; Executive Producer: Chris Peterson; © 2013 Tune In to Nature.org November 2013 Narrator: Michael Stein