Size: L: 35 cm Wt: 150-250 g. Males and females are similar. Seasonally dimorphic. This species requires two years to reach full adult plumage.
Adult winter: mantle, inner wing coverts, and innermost secondaries gray; rest of secondaries, greater coverts, outermost and median lesser coverts, and inner primaries white; alula, outer wing coverts, and outer primaries black (this forms a striking, tri-colored wing pattern, with a large, white wedge on the trailing edge, and a large black band on the outer leading edge); head white, with slate grey patch or half-collar on nape; underparts and tail white; bill black, with yellow tip; legs black
Second winter: similar to adult winter, but with some irregular black marks on wings and tail
First winter: similar to adult winter, but with much irregular black markings on wings; black tail band; bill black, with no yellow tip