The nomenclatural history of the two forms of white-tailed black cockatoo is discussed. Their correct names are Calyptorhynchus baudinii baudinii Lear for the long-billed form, and C. b. latirostris Carnaby for the short-billed form. C. b. latirostris differs from baudinii in having a slightly shorter wing and shorter culmen, there being virtually no overlap in the range of culmen lengths between adults of the two subspecies. The adult skull of baudinii is wider and higher, with a longer culmen, lower mandible and gonys than latirostris. C. b. baudinii is found in areas with an annual average rainfall of 750 mm or more, whereas lativostris occurs where it is 300–750 mm. C. b. baudinii appears to be resident throughout the year whereas latirostris moves to the higher-rainfall areas during the non-breeding season, returning to the drier areas during the breeding season. For food baudinii depends on the seeds of the marri, Eucalyptus calophylla, whereas latirostris depends on seeds from the small hard fruits of species of Hakea and Dryandra. A mechanism for the separation of the two forms during the breeding season is suggested.