Lesser scaup duller and have hardly any white at the bill base. Both sexes have white secondary remiges, a blue-grey bill with a black "nail" at the tip and grey feet; the drakes have a bright yellow iris, while that of females is orange or amber and that of immatures is brown. Downy hatchlings look much like those of related species, with dark brown upperparts and pale buff underparts, chin, supercilium and back spots. These birds are not very vocal, at least compared to dabbling ducks. Hens give the namesake discordant "scaup, scaup" call; in courtship drakes produce weak whistles. Hens vocalize
Greater scaup 20% heavier and 10% longer than the closely related lesser scaup. The male has a dark head with a green sheen, a black breast, a light back, a black tail, and a white underside. The drake or male greater scaup is larger and has a more rounded head than the female. The drake's belly and flanks are a bright white. Its neck, breast, and tail feathers are a glossy black, while its lower flanks are vermiculated gray. The upper wing has a white stripe starting as the speculum and extending along the flight feathers to the wingtip. Legs and feet