(photo above of a male Mallard and a female American Black Duck)
While observing a large group of Mallard Ducks yesterday I also noticed a few American Black Ducks among them. I then saw one duck which had a few charactistic features of both species. This was an American Black Duck x Mallard hybrid; (see photos above right and below)the result of an Amercian Black Duck and a Mallard breeding.
reference source: The Sibley Guide to Birds; by David Allen Sibley, p-83