CHAPTER IV 



(ECOLOGICAL 



Peculiarities of distribution. Continuous and discontinuous areas. Zoo- 

 geographical regions. The northern and southern hemispheres and the origin 

 of life. Some British birds and the lessons they teach in regard to the migra- 

 tion of animal life from north to south. Factors in the formation of isolation 

 areas. The haunts of birds. 



Geographical Distribution 



IT is a matter of common knowledge that in passing from 

 one region of the world to another strange types of birds 

 are sure to be met with, and it is commonly supposed 

 that the tropics are especially rich in this respect. This, how- 

 ever, is by no means true, nor are the differences between the 

 various types encountered in the different regions of the world 

 correlated with the distance which separates these several regions. 

 Thus, as has been more than once pointed out, the birds of 

 Great Britain and Japan bear a remarkable likeness one to 

 another, a much greater likeness than obtains between the 

 birds of Africa and the adjacent island of Madagascar. Yet 

 one-fourth of the circumference of the globe separates the first 

 two countries, while the last two are divided only by a few 

 miles! 



Again, a very varied avifauna may be found within the 

 confines of the same country; and this especially where the 

 surface of the land is diversified by mountain and moor, forests, 

 swamps and lakes. And when this avifauna as a whole 

 comes to be more closely studied, it will be found to contain 

 more or fewer types met with in no other part of the world, 

 so that the area over which such forms are spread is to be re- 

 garded as forming a distinct zoological province. 



The differences between the birds met with in any given 

 country are due to one or Other, or a combination of several 



