Waders hopping around on one leg, is that normal?

Just been out watching ducks, waders and gulls in a quiet bay and noticed a redshank hopping around on one leg. Thought the other must be missing but then I saw another one do it, then an oyster catcher doing the same, then another one!

I know birds stand on one leg but not hopping around on one. Surely they can't all have had missing limbs. Is this normal?

Thanks in advance