188 AJJNIVIIRSARY ADDRESS 



matter from those normal and annual changes of quarters 

 to and from the breeding haunts, which we collectively 

 denominate by the term Migration. 



The two, however, have this much in common that 

 they both involve to a greater or less extent the idea, 

 of " Expansion," and hence it is, no doubt, that so much 

 confusion has arisen. 



Wherever the original home of any group or species 

 of birds may have been, it is clear that, as the numbers 

 multiplied by natural and ordinary reproduction, an 

 increase in the area of habitation would be the necessary 

 result. Granted, for the sake of argument, that no 

 ailverse circumstances acted as obstacles in any one 

 direction more than another, the tendency would be to 

 circular expansion, on every radius, as it were, of a 

 circle ; a species might thus extend its range and 

 eventually have a geographical distribution differing in 

 some degree from the original, which would undoubtedly 

 to that extent affect the direction of migration. 



This expansion, however, is not in itself of a migratory 

 nature. By the term Migration we imply that after 

 the parents have succeeded in rearing their broods, the 

 great majority both of old and young leave their summer 

 quarters for other climes, to return for the next breeding 

 season. Possibly, indeed, all birds as species (though 

 not necessarily as individuals) act thus to a greater 

 or less degree ; but, before we can state this as a positive 

 fact, much more must be ascertained regarding their 

 movements, especially in the countries adjoining the 

 tropics, and in the Southern Hemisphere. 



Before migration takes place flocks are commonly 

 formed,* the members of which journey in company to 



* The youns: of most species being driven away whether by the 

 parents (as in some cases they certainly are) or merely by the 

 need of obtaining their food, do not at first flock — the flocking 

 seems to be brought about by their meeting at places where food 

 cau most readily be got. 



