Jan 21 2008
What a cold night! Temperatures in the single digits! Again I thought of how the birds are coping with cold.
Chuck Tague’s beautiful picture of Canada geese made me wonder how they can swim in near freezing river water and stand on ice for hours. It turns out that birds have special adaptions to keep themselves warm.
Feathers are one big advantage. Not only do they naturally conserve heat but the feathers closest to a bird’s skin are downy. Birds fluff their feathers to expand the down when the weather’s cold, making the little birds look like butterballs.
You can see the effect of feather insulation at this link showing infrared photos of a parrot on a person’s arm. The person’s arm looks “hot” but the parrot’s body looks “cool” because its feathers are such good insulation.
Another cold weather advantage for ducks and geese are their waterproof feathers and a layer of fat under their skin. The fat keeps them warm in cold water and their feathers keep them dry.
This leaves the problem of warming their feet. Birds can tuck a foot up under their feathers but this is impractical for very long.
So how can geese stand on ice in their bare feet? Water birds have an unusual circulatory system in their legs and feet. The veins and arteries in their legs are intertwined so that cold blood leaving their feet is warmed by the arteries delivering warm blood. (Open the comments below for a more accurate explanation from Dr. Bledsoe of Univ of Pittsburgh.)
Perhaps this means birds’ feet are a little colder all the time, but it doesn’t bother them. The advantage is that their central body doesn’t have to cope with cold blood returning directly to their hearts.
We humans don’t have these advantages so my feet are mighty glad they’re indoors right now.