158 



THE MIGRATION OF BRITISH BIRDS 



and which I propose to discuss in greater detail in a 

 later chapter {conf. p. 192 et seq). 



A brief ;yj"?^;«/ of the facts (and the deductions drawn 

 from them) contained in the preceding and the present 

 chapter will perhaps help to simplify what is undoubt- 

 edly a very intricate subject, and enable the reader 

 better to grasp the importance of their bearing upon the 

 question of avian dispersal. We commenced Chapter 

 III. by propounding a Law of Dispersal, which I think 

 very closely governs the facts set forth in that and 

 the present chapter. By means of this Law and its 

 corollaries we are able to explain many apparent 

 anomalies of avian distribution. For instance, they 

 will explain why the Arctic Tern actually breeds in 

 Alaska, yet returns to South-eastern Asia to winter. 



