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.

More info and transcript at BirdNote.org. 

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