|Photo from Wikimedia Commons|
When it’s cold outside, the lack of insulation on birds’ legs makes them a site of potential heat loss. But birds’ feet and legs are made up of mainly bone, tendon, and scaly skin. And unlike humans, birds don’t have sweat glands in their skin to produce any moisture to freeze.
Certain birds like waterfowl also have a heat exchange system in their legs. It is a specialized circulatory pattern to reduce heat lost through the feet when standing in cold water. The arteries and veins in the legs of many birds lie in contact with each other and function as a countercurrent heat exchange system to retain heat.
Similar to a radiator, arterial blood reaching the feet is already cool and venous blood reaching the core has already been warmed. In addition, by constricting the blood vessels in its feet a bird may further decrease heat loss by reducing the amount of blood flow to their feet at low temperatures.
So while the core temperature of a duck or gull standing in ice water may be 104 degrees F, its feet may be only slightly above freezing.
Read the full article on Temperature Regulation and Behavior at: http://www.stanford.edu/group/
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