Body: Medium-sized duck, 1 3/4 - 2 1/4 pounds, 17-20 inches long. Black back contrasts with white belly. Iridescent green head. Eyes gold. Round white spot on cheek. Bill short and black. Feet yellow-orange. Wings: Coverts and speculum form white patch; remainder of wing black. Voice: Piercing speer. In Flight: White on body. Dark head. White on trailing edge of underwings. Fast wingbeat causes distinct whistling sound.
