3i6 THE DISTRIBUTION OF AUSTRALIAN LAND-BIRDS. 



In comparing the species of area i and 7 it is to be 

 seen (i) that the birds of area i are derived from area 2, 

 while the birds of area 7 are derived from 2, 3, 4, and 6. 



The mass of the species that are found in areas 2, 3, 

 6, and 7 conjointly are not included in areas 8 and i. It is 

 noticeable in the census I prepared to get these data that 

 areas 7 and 6 are strongly connected by common species. 

 I take it that the Darling River and the Lake Eyre Basin, 

 by means of their water ways, have been important 

 feeders of the eastern half of area 7. 



If the Cooper and Diamintina at one time flowed into 

 the Murray Basin, this was certainly a good opportunity 

 to reach Central Australia from the south-east. Since 

 that period Central Australia had its Lake Eyre subsi- 

 dence — a period of good food for the birds. Then fol- 

 lowed the salting of the central lakes, and a period of 

 great stress for all the animals. It is probable that the 

 bird population was so reduced that a second series then 

 worked up from area 6, Hke those of that area. 



The Great Valley of South Australia in a series of 

 suitable seasons would offer facility for birds of area 6 to 

 emigrate into the valleys of the Cooper and Diamintina. 



That the species of area 7, for the most part, came 

 from areas 6 and 3, and for the least part from areas 2 

 and I, appears to be so. The watershed between Hughen- 

 den and Cloncurry may have had some small barrier 

 effect in the north. 



In comparing areas 2 and 3 it will be seen that a 

 strong affinity exists. In area 2 there are 342 species, in 

 area 3 297 species. Excepting a few species these 297 

 are found in area 2. The further south this emigration 

 course extends the weaker it becomes in specie-. The 

 tables show the decreasing values of 2, 3, 4, and 5, indi- 

 cating the area 2 to be by far the strongest in species; 

 then 3, 4, and 5, each in order getting weaker than the 

 last. 



Between the Hawkesbury and Richmond Rivers 

 (areas 3 and 4) we get a change of vegetation that affects 

 the avifauna — a plant-zone barrier. 



(i) See Tables I. and III. 



