I'm pretty sure that I've found my ninja duck!
I think they're a scoter of some variety or another.
the Black or American Scoter
White Winged Scoter
Also, K, remember my theory about ducks? There are two types of ducks in the world, Mallards and not-Mallards? I'm mostly right! Apparently the majority of domestic ducks are descended from Mallards (with one, the Seneca Duck being descended from the American Black Duck and two being descended from the Moscovy Duck). Also, Mallards are in the largest family of duck-like objects, and can mate with almost any of them. Some species are in danger of being wiped out because they have too much Mallard loving. I love being vindicated about stupid shit. :-P