58 ORIGIN OF MIGRATION. 



Origin of Migration. Why do birds migrate ? It 

 is true that in temperate and boreal regions the return 

 of cold weather robs them of their food, and they retreat 

 southward. But many, in fact most, birds begin their 

 southern journey long before the first fall frost. We 

 have seen that some species start as early as July and 

 August. Furthermore, there are many birds that come 

 to our Gulf and South Atlantic States to nest, and when 

 the breeding season is over they return to the tropics. 

 Surely, a lower temperature can not be said to compel 

 them to migrate. Even more remarkable than the south- 

 ward journey in the fall is the northward journey in the 

 spring. Our birds leave their winter homes in the tropics 

 in the height of the tropical spring, when insect and vege- 

 table food is daily increasing. They leave this land of 

 plenty for one from which the snows of winter have 

 barely disappeared, often coming so early that unseason- 

 able weather forces them to retreat. 



I believe that the origin of this great pilgrimage of 

 countless millions of birds is to be found in the existence 

 of an annual nesting season. In my opinion, it is exactly 

 paralleled by the migration of shad, salmon, and other 

 fishes to their spawning grounds, and the regular return 

 of seals to their breeding rookeries. 



Most animals have an instinctive desire for seclusion 

 during the period of reproduction, and when this season 

 approaches will seek some retired part of their haunts or 

 range in which to bring forth their young. Salmon may 

 travel a thousand miles or more from the ocean, and, 

 leaping the rapids or other barriers in their way, finally 

 reach the headwaters of some river where their eggs 

 may be deposited in safety. Seals migrate with regu- 

 larity to certain islands, where their young are born. 

 Even our domesticated Hens, Turkeys, Ducks, and Pea- 

 fowl, if given freedom, will travel a greater or less die- 



