The red-tailed black cockatoo (Calyptorhynchus banksii), also known as Banksian- or Bank's black cockatoo, is a large cockatoo native to Australia. It is more common in the drier parts of the continent. Five subspecies are recognised, differing most significantly in beak size. Although the more northerly subspecies are widespread, the two southern subspecies, the forest red-tailed black cockatoo and the south-eastern red-tailed black cockatoo are under threat. Adult red-tailed black cockatoos are around 60 centimetres (24 in) in length and sexually dimorphic. Males are completely black in colour, excepting their prominent red tail bands; the slightly smaller females are brownish-black with yellow barring and spotting and have yellow-orange tail stripes. The species is usually found in eucalyptus woodlands, or along water courses. In the more northerly parts of the country, these cockatoos are commonly seen in large flocks. They are seed eaters and cavity nesters. Of the black cockatoos, the red-tailed black is the most adaptable to aviculture, although black cockatoos are much rarer and much more expensive outside Australia.