On the way home from work the other day, I saw a flock of galahs and sulphur-crested cockatoos feeding at the side of the road. Then I saw a couple of yellow-tailed black cockies near Queenscliff. And yesterday, a quartet of corellas picked through the newly-mown lawn in a park. This really is a land of parrots.
Although they all belong in the genus Cacatua, corellas are more closely related to the other bare-eyed cockies than they are to sulphur-crested cockatoos. Two species of corella occur only in Australia, a third extends its range from Australia to a tiny bit of southern New Guinea. Of the non-Aussie bare-eyed species, Goffin's cockatoo (C. goffini) is found in the Tanimbar Islands, W of New Guinea and Ducorps' cockatoo (C. ducorpsii) lives in the Solomon Islands to the E of New Guinea. How exactly those five species are related is yet to be determined. My bet is that both of the non-Australian species will sit in tight with the little corella (C. sanguinea). But I spend a lot of my time throwing money away, so don't trust my tips.
Still, it makes yer think, don't it?
Brown, DM & Toft, CM. (1999) Molecular systematics and biogeography of the cockatoos (Psittaciformes: Cacatuidae). The Auk 116(1): 141 – 157. (PDF)