5S 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 soathward. But many, in fact most, birds begin their southern journey long before the lirst fall frost. We have seen that some sjDeeies 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 dis-
