Size: L: 25 cm Wt: 65 g. Males and females are similar. Seasonally dimorphic. This species requires two years to reach full adult plumage.

Summer Adult: mantle and wings slate grey, with blackish wing-tips; head and underparts black, except undertail coverts, which are white; tail slate grey; bill black; legs dark red

First Summer: mantle and wings medium grey; head with dusky or blackish crown and nape, and blackish ear patch that is continous with dark crown; underparts white, with black smudges, and dark bar on side of breast; tail grey; bill and legs as in adult

Juvenile: mantle and scapulars dark grey-brown; wings grey, with dark grey carpal bar, and brownish markings on secondaries; head white, with dusky crown, nape, and ear patch; underparts white, with dark bar on side of breast, but no black smudging; tail grey; bill blackish, may show some pink at base; legs pink

Nestling: semiprecocial and downy; down long, soft; upperparts, throat, and chin buff, mottled with black; breast greyish-white; flanks and belly buffy grey; forehead, around base of bill, and patch around eyes white; bill brownish; legs dark pink