A man standing with his bare feet in cold water would not survive long, but a wading bird can stand in cold water all day, and the whale and seal swim in the arctic with naked fins and flippers, continually bathing them in freezing water.
All such warm-blooded creatures have to maintain a steady body temperature. How do they manage to do this?
They use what biologists call a “counter-current exchange.” It is a method of heat exchange used in industry.
In animals it is called rete irabile, or “wonder net.” The blood in one vessel flows in the opposite direction to the adjacent vessel, and in this way warm blood passes on its heat to the colder blood. It is equivalent to a double layer of circulating blood.