Biochemical Systematics of the Australian Cockatoos (Psittaciformes: Cacatuinae)

The genetic and evolutionary relationships of the Australian cockatoos (excluding Probosciger) and of the cockatiel, Nymphicus hollandicus, were examined by the technique of isozyme electrophoresis. A cladistic analysis of data from 28 loci showed that Nymphicus is more closely related to cockatoos than to any ofthe non-cockatoos; accordingly Nymphicus should be included within the Cacatuinae, but in a monotypic tribe. The other genera form two well defined groupings. One comprises all of the white cockatoos (Cacatua) and the gang gang Callocephalon fimbriatum, and the other, the black cockatoos (Calyptorhynchus). Within the white cacatuine cockatoos there seem to be at least two minor groups. One, clearly indicated by the electrophoretic data, comprises the galah Cacatua roseicapilla and Australo-Papuan corellas, all of which have short plain crests and usually coloured periophthalmic skin. The other, neither denied nor confirmed biochemically, is a looser assemblage characterized by coloured up-curving crests and plain periophthalmic skin; it included the sulphur-crested cockatoo Cacatua galerita and the pink cockatoo Cacatua leadbeateri, and their allospecies on islands north of Australia. Isozyme electrophoresis of the loci examined in this study could not differentiate members of the Calyptorhynchus funereus superspecies, nor of the Cacatua tenuirostris-pastinator group of corellas. The results are therefore in accord with other studies that show that isozyme electrophoresis has limited application in elucidating species boundaries in birds.