64 RUDOLF SÖDERBERG, STUDIES OF THE BIRDS IN NORTH WEST AUSTRALIA. 
same colour. 'The lower larger wing-coverts, the inner-beard of primaries and secon- 
daries something between »grebsrot n:r 4 and atlasrosa n:r 3» (Reporte de couleurs), 
the top of the wings and the tail white. The feathers at the base of the upper-bill 
»krapprote», forming a red streak down towards the lores. Narrow, naked yellowish 
ring around the eye. The crest white at the top, otherwise clearly »krapprote» 
(n:r 86 Reporte de couleurs) without any yellow stripe or yellow centre-spot in the red 
feathers. Bill yellowish gray, legs grayish. 
The total length 38 cm., the wings 25 cm. long, the tail 15,5 cm. long, the bill 
2,65 cm. long, the tarsi 1,8 cm. long. 
The specimen is a full-grown old male. It is not in moulting. 
The species Cacatua leadbeateri ViG. (Math. handl. n:r 321) is not seen in this 
northern part of West Australia. During my stay in Mowla Downs, however, I 
obtained the specimen described above. The distribution or rather »spreading-zera» 
of the species thus extends from New South Wales and the bordering parts of Vic- 
toria, through Central Australia, right up to the territory south of Fitzroy in Kim- 
berley. Anyhow it is worthy of mention that the 6 birds, out of which this spe- 
cimen was shot, were the only ones that could be observed during my stay in 
Mowla Downs. This occurred at the beginning of Nov. 1910, in the driest season, 
when the birds are generally straggling widely about. After the rain had been falling 
some days, the birds were gone. It is therefore probable that the species does 
not go farther towards the North West than at most to some more suitable border- 
lands of the desert. 
Whether a communicating area of extension over the above-mentioned places 
exists in the case of Cacatua leadbeateri, or if, on the other hand, it is interrupted 
by the inmost (waterless) desert belt, it is impossible to decide as yet. At any 
rate the specimens of this species in the South East and North West show considerable 
variation due to geographical conditions. 
The most conspicuous thing in the North Western form is the absence of the 
yellow part of the crest, which is otherwise so striking in the Sout Eastern ones. 
Next the difference in size is Very conspicuous. The form described here is in every 
respect the smallest one, as will be seen from the description above. Living in a 
desert county it is also lighter in colour than the principal form. 
A collection of the former specimens ought to show the variations more clearly. 
The only thing I have to mention is what I learnt from two specimens of C. lead- 
beateri from the inner parts of Australia, kept in the Zoological museum in Adelaide. 
The ornithologist of the museum, Mr. F. BR. ZiETtzZ, kindly showed them to me and 
said that they were smaller than specimens from the South East and had noticeably 
smaller yellow parts in the red crest, a fact that I was able to confirm myself. 
Probably there are real transitional forms between the two extreme forms coming 
from geographical districts which lie between them. 
It is interesting to mention that I got a letter, dated the 12th of Dec. Northern 
Territory, from Mr. J. RoGERS, who tells me that he has been at the place where I 
