King eiders are a moderately large sea duck, weighing 1200-2100 g (2.6 – 4.6 lbs). Male king eiders are one of the most ornately plumaged ducks in North America. In breeding plumage (late fall through midsummer), males sport a large orangeyellow knob between their bill and forehead. Their forehead, crown, and nape is pearl blue, with iridescent pale green cheeks and a reddishorange bill. The lower portion of their head, neck, upper back, and breast is white with the remainder of the body black. The longest feathers along their upper flanks have triangular extensions that form a sail-like projection on their back.
Sea Duck Information Series fact sheet
King Eider Species Knowledge Summary and Information Needs [PDF]