WHY DO GEESE SLEEP ON ONE LEG? Birds regulate their body temp. by pushing hot blood to the legs where it is cooled by the surrounding environment. During sleep, they tuck one leg under the body to reduce the amount of heat lost through the legs since they are not active and metabolism has slowed they are at risk of becoming hyopthermic (very unlikely in pet birds). At least this is the case for the wild birds that deal with drastic temperature changes. Pet birds, who are kept inside, are just doing what is an instinctual behaviour if the room is warm enough.