Note from John H. Ginaven:

Sighting of an American Black Buck (Anas rubripes), at Minersville Reservoir State Park, Utah on August 8, 1994, at about 3:15 PM.
   The bird was seen by Merrill Webb, Rosemary Seidler and me at a distance of about 100 yards at the north end of Minersville Reservoir.  It was standing on the mud flat near the edge of the water, alone but about 10 feet from two female Mallards.  The bird did not seem to associate with any other ducks.  I spotted the bird from a greater distance and immediately said it was an American Black Duck, not realizing that it was rare in Utah.  Merrill was surprised, so we studied the bird for about 10-15 minutes, moving closer as we did.  I saw the dark brown ("black") body and wings contrasting with the light brown head.  The demarkation line between head & body was distinct .  I saw the reddish orange legs and did not observe any white on the tail or back of the body.  I was able to compare the size with the nearby female Mallards and found it as big or slightly bigger.  The female Mallards were clearly lighter brown with little contrast between the head & body.  I observed the blue speculum on the female Mallards but could not see the speculum on the black duck.  We did not observe the bird in flight to see the underwings and under body color, although the underparts did see all dark while it stood.  The bill was dark indicating a female. 
   The lighting was overcast but reasonable.  We used a 15-60 Swift spotting scope as well as binoculars.
   I have had 22 year experience with American Black Ducks in Pennsylvania and the eastern U.S. I am also familiar with Black Duck x Mallard hybrids.  I do not believe it was a hybrid.
   I can be contacted at:

John H. Ginaven
1268 Delmar Avenue
West Chester, PA  19380
(610) 696-5665