VOL. 18 (6) JUNE2000 241 AUSTRALIAN BIRD WATCHER 2000, 18, 241-243 Further Comments on the Taxonomic Position of the Galah Cacatua roseicapilla

by JOHN COURTNEY, 'Ashgrove', Swan Vale, via Glen Innes, N.S.W 2370

The Galah Cacatua roseicapilla has been shunted back and forth between · monophyletic Eolophus and the polytypic white cockatoos Cacatua ( = Kakatoe ). Without fossil material and having no 'intermediate forms', the systematic position of the Galah is subjective according to the importance given to the characters used to define it as a species. Since the papers by Courtney (1993, 1996), more data have accrued, and are here discussed.

Data According to Joshua & Parker (1993), the white cockatoos have a common karyotype from which that of the Galah is 'significantly different'; that of the Galah has 'considerable similarity' to that of the Cockatiel Nymphicus hollandicus. However, Adams et al. (1984) stated that the Galah is closely related to the Western Corella Cacatua pastinator and Little Corella C. sanguinea on biochemical data. This is questioned by Schodde (in Schodde & Mason 1997) who, because of its cranial similarity to the Cockatiel and Gang-gang Cockatoo Callocephalon fimbriatum, prefers to have the Galah as sole representative of Eolophus. Sibley & Ahlquist (1990), from DNA-DNA hybridisation, found Major Mitchell's Cockatoo Cacatua leadbeateri closer to the Galah than the Cockatiel, and Christidis & Boles (1994) included the Galah with the white cockatoos. As bird-lice (Mallophaga) evolve along with their hosts, they can have value as chronological indicators of when birds separated as species (related lice occur on related birds), a principle known as Fahrenholz's Rule (Welty 1964). Among the Australian cockatoos only the Galah and Little Corella have three species of Mallophaga in common (Murray et al. 1999). The other cockatoos mostly have fewer genera of Mallophaga and what they have belong to species different from those of the Galah and Little Corella.

Discussion The mitochondrial DNA analysis of cockatoos (Brown & Toft 1999) echoes the suggestion of Courtney (1996) that cockatoo evolution was 'from black, to grey, to white'. Further, the division between the white cockatoos (including the Galah) and other cockatoos, the relationship between the Galah and white cockatoos, and the 'closer' relationship between the Galah and the corellas, had been anticipated by Courtney (1974, 1993, 1996) on behavioural evidence. Irrespective of whether the Galah is the male or female parent, the difference in karyotype has not prevented it from producing viable hybrids, male and female, with several species of white cockatoos Cacatua. According to G.A. Smith (in litt. 1999), a male hybrid between a Galah and Lesser Sulphur-crested Cockatoo Cacatua sulphurea proved fertile when paired back to a Galah. The Galah had nine of ten traits that Courtney (1993) used as characters to designate white cockatoos Cacatua. With hindsight it was ten, as it has since been shown that if melanin is removed by genetic mutation (Sindel & Lynn 1989) or AUSTRALIAN 242 COURTNEY BIRD WATCHER by a solvent (G.A. Smith in Litt. 1999) from the Galah's plumage under the wings and tail, there is a pink suffusion. According to Schodde (in Schodde & Mason 1997), two of the characters used by Courtney were 'misreported' (colour of down, and white in the plumage). However, down was not a character used, and differentiating the white of a Galah's rump from the white Qf white cockatoos is pedantry when, as juveniles, many of the white cockatoos have their feathers washed with grey, and a mutation of one gene (G.A. Smith in Litt.) strips the Gal ah of melanin to make many of its feathers as white as those of the whitest of the cockatoos.

Conclusions Speciation in Mallophaga correlates with speciation in the cockatoo host; Fahrenholz's Rule does not support splitting the Galah from other Cacatua spp. With characters that are genetically determined, the more characters considered and the more divergent these characters are, then the more of the genome is compared. Morphology, behaviour and biochemistry are linked to functioning DNA. The information provided by mitochondrial DNA (Brown & Toft 1999) backs up that of more traditional methods by both agreeing that a separation between black-cockatoos Calyptorhynchus spp., Cockatiel, and Gang-gang preceded that of the Galah and the white cockatoos. In turn, this questions the 20-million-year-old Riversleigh fossil cockatoo being a proto-Cacatua, for this would push the split between Callocephalon and Cacatua even further back, making hybridisation between the two genera unlikely (O'Neill 1999), yet a viable hybrid from a chance union is known (Appleton et al. 1988). The possibility should be considered that the fossil is the common ancestor of Nymphicus, Callocephalon and Cacatua, making Cacatua more modern than now believed. Karyotype, length of begging call, grey in adult plumage and vestigial cranial characters in the Galah, shared with the Cockatiel and Gang-gang, can reasonably be regarded as retention of ancestral features. These, combined with possession of all ten characters used to define modern Cacatua cockatoos, point to the proto-Galah being a foundation member of the genus. Thus, little substantiates removing the Galah from the white cockatoos Cacatua spp.

Acknowledgements I thank Mr George A. Smith of Peterborough, England, and two anonymous referees who commented most usefully on this paper; Mr Stephen Debus for his guidance in general and for reference material provided; and Mrs Julia Hurley for diligent editing.

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