Size: L: 50 cm. Wt: Males: 1540 g. Females: 1220 g. Sexually dimorphic in size and colour. This species is not seasonally dimorphic.

Male: body black; white crescent under eye; bill red with large black knob at base; white wing patch.

Female: body blackish-brown; faint patches on cheek and at base of bill; white wing patch; bill reddish-black, with no knob.

Juvenile: young males similar to females, but with facial markings somewhat clearer, bill redder; young females with very obvious facial markings, and completely dark bill.