Those are called Mule Ducks, and for my money... they are one of the prettiest ducks in the air! Even though they aren't a legit species.

On my old computer I had a bunch of pictures of hybrids that a bird collector had ammassed over the years.

He had a Redhead/mallard, pintail/woodduck, BWT/Shoveler, Gadwall/Mallard, Golden Eye/Bufflehead, all kinds of wierd stuff.

I have personally shot hybrid black ducks/mallards... not terribly uncommon, heck I think its more uncommon to kill a mature male 100% pure black duck anymore.