Why do birds sleep like that?

[The_Asbestos_Mango]

Nearly every bird I have ever had the opportunity to observe sleeping (and I have seen many birds asleep, ranging from budgerigars to Peregrine falcons) has slept standing on one foot with its head turned around backwards and its beak stuffed into the feathers on its back. The sole exception was a Peregrine falcon named Arty, who, for some strange reason, liked to sleep leaning his beak against the lighted sign on a bank building, but then Arty was a bit strange…

This does not seem to be the ideal position for sleeping.

But they all do it. Ducks, parrots, finches, falcons.

Why?

[Colibri]

Probably because it minimizes heat loss. Birds lose heat largely through their unfeathered surfaces, such as the legs and bill. By pullling one leg up into their feathers, and placing the bill inside the plumage too (and perhaps exhaling heated air into it) they will save the maximum amount of heat when they are not active.

[mittu]

I’m not too sure about the one-legged thing but this website addresses the issue of the wing tuck.

As for how they sleep, most birds use the old “wing tuck” method. Actually, birds don’t tuck their heads under their wing. Instead they rest their heads on their backs while they nuzzle their beaks into their back feathers. Sleeping with their head tucked on their back allows birds to rest their neck muscles and also makes for better heat conservation.

[Scarlett67]

The one-legged posture also allows them to rest their feet, one at a time.

Scarlett, who has owned 4 birds (parakeet, lovebird, two cockatiels)