That chickens need a flat perches at least 4" across to cover their feet with their feathers, otherwise they get frostbite and their feet drop off.
I'm not sure who was the first person to say this, but I'm pretty sure wild pheasants would be extinct by now if it were the case.
The above perch is a branch about 2.5" in diameter. As you can see, the chicken uses these 'flaps' of feather to cover his feet.