The little sliver of white across the side of this male American Wigeon, at Cape May Point State Park last week, is all you can see of the big white patch covering the bird's upperwing coverts. Notice how the scapulars drape over the wing from above, and the wing folds into the flank feathers below it. Beware field guides that show wing markings on sitting ducks, because often the entire wing is hidden by the body plumage. This is something that anyone who has tried to identify female wigeon, female Gadwall, or White-winged Scoters are well aware of. It's a wonderful adaptation to keep a swimming bird warm.
Below, the bold upperwing pattern of a male American Wigeon taking off from Cox Hall Creek WMA, last winter. Click to enlarge the photos.