In a recent BBC news article it said that scientist finally understand why birds stand on one leg. Thermo-regulation was the answer. I can understand that in the winter but why in the summer? This photo of the night heron was taken in Louisiana and the temperature was 92f.
Gary- I'm not really sure I believe the new science on this but I admit that I've not read the original paper so I'll reserve judgement. Being skeptical is part of being a scientist. However, here's some thoughts:
Birds "run" a core temperature of about 41°C or ca. 106°F so at 92°F this bird is still experiencing a 14°F thermal gradient between inside and outside. Birds don't sweat and use blood flow to bare skin and sparsely-feathered areas to regulate body temperature. A lot of food energy in homeothermic ("warm-blooded") animals is put towards maintaining body temperature and loss of energy through exposure of bare skin has costs so an optimal animal fine-tunes it's thermoregulation to save as much energy as possible.
However, having said this, I remain skeptical about a thermoregulatory answer because birds are well known to have a "counter-flow" system in the veins and arteries of the legs such that the heat energy in warm arterial blood is recovered by adjacent veins and taken back to the body core. Thus there is very little energy loss through the legs and feet anyway.
Thanks John. I lived in the Canadian arctic for quite a while and the Ptarmigans rarely seemed to stand on one leg. Mind you they do have feathers down their legs and tend to sit on them instead. A big difference between Louisiana and the Yukon.