[you’d never believe how difficult it is to identify some birds; it’s almost as hard as identifying insects… but not quite; suffice it to say I was never able to determine the species of these two waterfowl; it’s possible the darker one is a hybrid (mallard x black?), but I’m guessing at that; the white one could be a white mallard (who’d ever heard of such a thing!), but again I’m guessing; I don’t believe either of those guesses given the size of these birds (at least half again as large as a normal mallard), although I could be wrong; if you have any ideas on what they are, please speak up; what I think I know is that the white one is a female and the dark one is a male]
[Update] I have since identified the white duck as a pekin duck (a.k.a. domestic duck, white pekin duck, or Long Island duck; Anas domesticus).