Size: L: 50cm. Wt: Males: 1090 g. Females: 1010 g. Sexually dimorphic in size and colour. This species is not seasonally dimorphic.
Male: body completely black, streamlined; bill black, with prominent orange knob at base.
Female: body blackish-brown; whitish cheeks, throat, and front of neck; bill black, no knob.
Juvenile: similar to female, but cheeks, throat, and neck darker, body more mottled.