INTRODUCTION 15 



along our northern coast is distinctly aesthetic, 

 when compared with the sombre hues of as many 

 million petrels that fringe the southern coasts. 



Of the birds of Australia there are, say, eight 

 hundred species with innumerable variations. 

 Some of these latter may be considered races, and 

 they are important in the ornis of this land. Take 

 for example the species A B in map 3. A is the 

 northern race, because all the thousands of it are 

 smaller than B, those of the southern half of the 

 continent. In each case the westward trend has 

 taken the birds into western influences of food and 

 air, and has changed their plumages. The colour 

 pattern will mostly remain, while the intensity of 

 colour will lessen and alter. This is noticeable in 

 a 3 of the race A, which comes under the paling 

 effect of light desert air. A and B so carefully 

 change in Southern Queensland as to be the inter- 

 grades. 



In map 4, species A B is one example with eight 

 races; Yellow-tailed Tit- Warbler (Acanthiza chry- 

 sorrhoa). Its southern expansion is a d, and its 

 western margin e h. 



While the birds of the southern line grow larger 

 and darker, those of the same species of the western 

 margin grow lighter, with elimination of certain 

 plumage characters. The first line is in the damp 

 belt, the second in the dry one, with an effect so 

 gradual, yet so definite, as to give us birds at a d. 



