I was looking at some Mallard drakes on a local pond today, and I saw some strange behaviour. One of them was diving (that is to say complete submersion for a second or two and popping up several feet away). I know there are diving ducks, but I wouldn't associate this with Mallards, which normally up-end, with their bottoms sticking up in the air. Has anyone else seen this before, and is it common behaviour that I have just not been observant enough to notice before?