Size: L: 70 cm Wt: 1250-1600 g. Males are somewhat heavier than females. Seasonally dimorphic. This species requires four years to reach full adult plumage.

Winter Adult: mantle and wings very pale grey; wing with white leading edge and white tips; head white, with brownish streaking; underparts white, with some streaking on upper breast; tail white; bill yellow, with red spot; legs pink

Third winter: mantle and wings very pale grey; wing with faint brownish freckling; head white, with brownish streaking; underparts white, may have brownish mottling; tail white, with brownish freckling; bill yellow, with black tip; legs pink

Second winter: mantle pale buff or whitish, with sparse barring; wings pale buff, may have faint barring; head and underparts pale buff or whitish, may be faintly streaked or mottled; tail pale grey or buff, with mottled pattern; bill pinkish, with black tip; legs pink

First winter: mantle pale buff, with brownish barring; wings pale buff; head light brownish-grey or buff; underparts uniform brownish-grey, may have faint bars on sides of breast and flanks; tail plain pale grey or buff, with whitish and dark mottles and bars; bill and legs as in second winter