When the bird started bathing, it remained in one place long enough to catch on video. The effect of having only one foot is seen here, as the bird has difficult keeping in place - tending to float downstream - because it hasn't got sufficient grip on the stones (it obviously wants to be in a particular place). Also, it seems to jump about quite a bit - something it probably wouldn't need to do if it had use of two feet.
Click on the YouTube symbol to see it full size (not on the full screen symbol - which gives a pixelated view).