ISOLATION or TIIK M A I I 4 



Kaeh year the different pairs have been more 

 or less successful in rearing their young; each 

 year the young can be seen accompanying their 

 parents up to the time when the sexual instinct 

 arises ; and yet the actual number of pairs is on 

 the whole remarkably constant, and there is no 

 perceptible increase. It seems as if the numbers 

 of three and two respectively were the maxi- 

 mum the headland could maintain. But this 

 is no exceptional case ; it represents fairly the 

 conditions which obtain as a rule amongst 

 those species, granting, of course, a certain 

 amount of variation in the size of each terri- 

 tory determined by the exigencies of diverse 

 circumstances. 



If we take a given district, and devote our 

 attention to the smaller migrants that visit 

 Western Europe each returning spring for the 

 purpose of procreation, we shall find that the 

 movements of the males are subject to a very 

 definite routine. This, however, is not true of 

 every male ; some may be wending their way to 

 breeding grounds at a distance ; others may be 

 seeking the particular environment to which 

 theyjmay be adapted ; others again, having found 

 their old haunts destroyed, may consequently 

 be seeking new. 



Of all this there is evidence. Small parties 

 of Chiffchaffs pass through a district on their 

 way to other breeding grounds, flitting from 

 hedge to hedge as they move in a definite 

 direction with apparently a definite purpose ; 

 Reed- Warblers settle in a garden or plantation, 



