Which of these birds usually stands on one leg?

Flamingos pull one leg up close to their body to conserve heat that might otherwise be lost while standing in cold water—not just in the Andes, but in the tropics, too, where even a slight drop in water temperature could mean big losses, due to the length of a flamingo leg. It appears that flamingos share a primitive feature also seen in whales and dolphins: the ability to shut down half the brain while sleeping.

Source: Smithsonian Mag