Black Scoter Overview, All About Birds, Cornell Lab of Ornithology

The Black Scoter is divided into two subspecies. In the form found in Europe, the "Common Scoter," the male has a larger swollen knob at the base of the upper bill that is black on the sides with a yellow stripe on top, not entirely yellow.

The Black Scoter occasionally does a "Wing-flap" display while swimming, flapping its wings with its body held up out of the water. Unlike other scoters, it almost always punctuates a Wing-flap with a characteristic downward thrust of head, as if its neck were momentarily broken. Surf and White-winged scoters keep their heads and bills pointing more or less above the horizontal throughout a Wing-flap.

The Black Scoter is among the most vocal of waterfowl. Groups of Black Scoters often can be located by the constant mellow, plaintive whistling sound of the males.