WESTERN AUSTRALIA 203 



WESTERN AUSTRALIA 



Areas 9—79, 8—78 



1. The bird fauna of the north is divided from 

 the south by a desert. The origins of nearly all the 

 families in a and b, map 88, are separately derived 

 from the east of Australia, along a northern line 

 and a southern one; along the rainfall zones of 20 

 inches and 10 inches. In the latter case, prior to 

 the subsidence of the Australian Bight old coast 

 line, the rainfall was more in keeping with 20 

 inches. 



Some of those birds used to living in a forest of 

 40 inch rainfall in south-east Australia, gradually 

 went west. They are now preserved in the small 

 area of 40 inches in the south-west. Those birds 

 in the links between, through not accommodating 

 themselves to the wearing away of a 40 inch rain- 

 fall coast in favor of a 10 inch zone, died out. Thus 

 we get eastern and western representation of a 

 species with a broad gap. The less specialised 

 birds of b worked up the coast from Perth and 

 Geraldton districts to the Ashburton country with 

 an annual rainfall of 8 inches. This is their north- 

 ern limit. 



2. The northern line of expansion, "a," from 

 Queensland, was as much coastal as the southern 

 line, but with different types of birds. Here we 

 have the genera of a moist hot coast line, and the 

 finches of the parallel extensive grass lands. 



