Most birds you see standing on only one leg are doing an impressive balancing act while tucking the second leg into their feathers. This is much easier to recognize in large birds, such as flamingos, but the behavior itself is common to most birds. So, the real question is: why do they do that? The answer is that birds use their feet for temperature regulation. In most birds the legs and feet are unfeathered, and thus lose heat very quickly — the same way your exposed hands get cold in winter faster than your clothing-covered torso. That makes the bare feet great conductors: when the bird’s overall body temperature is too high, it can cool off by standing on both legs and letting the wind carry away heat. When the temperature drops too low, it can pull one leg up and lose less heat.