Bird’s legs have an adaptation called “rete mirabile” that minimized heat loss. The arteries that transport warm blood into the legs lie in contact with the veins that return colder blood to the birds heart. The arteries warm the veins. By standing on one leg, a bird reduces by half of the amount of heat lost through unfettered limbs. Birds also purposely create their own shadows in the water. Apparently egrets can blend better with their surroundings and look like a shrub to a fish by standing on one legs. The word “pedigree” which is ones family tree, comes from the French “Pied de grue” Cranes foot. This is something represented artistically as a tree with exposed surface roots or even a birds foot in old ancestral diagrams. Take a close look at the egrets leg and feet if you ever get the chance. The tough skin really does makes them look like tree trunks, and undoubtedly fools fishes seeking a bit of shade for cover too.