Size: L: 20-25 cm. Wt: Males: 65 g. Females: 55 g. Males and females dimorphic in size and colour. This species is seasonally dimorphic.

Breeding Male: body black, with greenish gloss; bill sharply pointed, blackish; eye yellow; legs black

Breeding Female: body dark grey, not glossy, upperparts somewhat darker than underparts; bill, eye, and legs as in breeding male

Fall Male: body dark brown to blackish, with rust-tipped feathers; brown eyebrow and moustache stripes; bill, eye, and legs as in breeding male

Fall Female: upperparts rusty brown, with grey rump and buffy eyebrow; underparts buffy; bill, eye, and legs as in breeding male

Juvenile: resemble fall adults; eye may not be yellow.

Nestling: altricial and downy; down long, thin, dark brown