Stobart wrote:Think it's just what they do to keep one leg at a time warm.
That's correct, but although I don't know whether this applies to cormorants,some birds with their legs regularly exposed to near-freezing temperatures have an aligned arrangement of veins and arteries in their legs which allows the cold blood returning to the body to be warmed by the warm blood going into the legs, so that the bird has to use less energy to heat up the returning blood. Very cunning. Eider ducks are an example. However, birds can and do get frostbite, particularly if they go from a relatively warm environment to a very cold one too quickly.