When I see this photo, I can't help but think the bird looks just slightly put off, and that "black eye" doesn't help the situation. Nevertheless, this is a beautiful photo.
I've seen this behaviour in ducks and geese fairly often. I think it may be a "comfort display," which are behaviours or activities that birds engage in when they are relaxed and not on alert. Grooming is another popular one, as is stretching.
on Jul 01
I have seen the ducks and geese in my area do this same one leg stand.
I wonder why they do this?
Are they trying to warm the other foot LOL?