Size: L: 40-50 cm. Wt: Males: 600 g. Females: 950 g. Males and females are similar in plumage, but dimorphic in size. This species is not seasonally dimorphic. Three subspecies are recognized in North America; F. p. anatum, F. p. tundrius, and F. p. pealei. Of these, only anatum and tundrius occur on the Great Lakes.
Adult, F. p. anatum: mantle dark slate blue; head and nape black, with black wedge extending below eye; throat whitish; underparts buffy, with heavy grey-black streaking; tail square, barred, with dark subterminal band; bill hooked, black with yellow cere; legs yellow, with large, taloned feet
Adult, F. p. tundrius: similar to anatum, but mantle somewhat paler, and underparts almost white, with less heavy streaking
Juvenile: mantle dark brown, may have some slate in primaries; head and nape with variable amounts of dark brown, and with brown wedge extending below eye; throat and underparts buffy or pale brown, heavily streaked with dark brown; bill hooked, black with grey cere; legs pale blue-grey, with large, taloned feet
Nestling: semialtricial and downy; first down sparse, whitish; second down long and woolly, buffy grey above, whitish below; irides dark; dere and legs pale grey