Have you ever watched ducks walking around in freezing temperatures and wondered why their feet don't freeze? And how do birds, including this Northern Flicker, sit on metal perches with no problem? Birds' feet have a miraculous adaptation that keeps them from freezing. Rete mirabile — Latin for "wonderful net" — is a fine, netlike pattern of arteries that interweaves blood from a bird's heart with the veins carrying cold blood from its feet and legs. The system cools the blood so the little blood that goes down to the feet is already cold, so the birds don't lose much heat. The small amount that goes to the feet is likely just enough to keep the feet from freezing.
Why Birds' Feet Don’t Freeze
Written by Frances Wood
This is BirdNote!
Have you ever watched ducks walking around in freezing temperatures and wondered how they keep their feet from freezing? The ducks seem oblivious to the cold, even as they stand on ice-covered lakes and streams. Or perhaps you’ve been concerned that the tiny feet of songbirds will freeze to metal perches. [Winter song of Pacific Wren]
Unlike our feet, birds’ feet are little more than bone, sinew, and scale, with very few nerves. But it takes more than a lack of nerves to keep their feet from freezing. A miraculous adaptation called rete mirabile is responsible. This fine netlike pattern of arteries that carry warm blood from the bird’s heart is interwoven with the veins carrying cold blood from the feet and legs. This interweaving warms the cold blood in these veins before it reaches the bird’s heart. This system keeps the bird’s legs and feet warm, even without leggings and slippers. [More song of songbird]
[Editor's note: Actually, the rete mirabile means that the blood that goes to the feet is actually quite cold, and the feet are cold, but not generally so cold that they freeze.]
And those little songbirds’ feet?—don’t worry. Birds’ feet lack sweat glands and stay dry. So, there is no danger of them freezing to metal perches.
What was that called again? Rete mirabile.
Call of Mallard and the song of the Winter Wren provided by The Macaulay Library of Natural Sounds at the Cornell Lab of Ornithology, Ithaca, New York. Mallard recorded by A.A. Allen, Winter Wren by G.A. Keller.
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© 2015 Tune In to Nature.org December 2013/2017 Narrator: Michael Stein