. Bird-life; a guide to the study of our common birds . disappeared, often coming so early that unseason-able weather forces them to retreat. I believe that the origin of this great pilgrimage ofcountless millions of birds is to be found in the existenceof an annual nesting season. In my opinion, it is exactlyparalleled by the migration of shad, salmon, and otherfishes to their spawning grounds, and the regular returnof seals to their breeding rookeries. Most animals have an instinctive desire for seclusionduring the period of reproduction, and when this seasonapproaches will seek some retired
. Bird-life; a guide to the study of our common birds . disappeared, often coming so early that unseason-able weather forces them to retreat. I believe that the origin of this great pilgrimage ofcountless millions of birds is to be found in the existenceof an annual nesting season. In my opinion, it is exactlyparalleled by the migration of shad, salmon, and otherfishes to their spawning grounds, and the regular returnof seals to their breeding rookeries. Most animals have an instinctive desire for seclusionduring the period of reproduction, and when this seasonapproaches will seek some retired part of their haunts orrange in which to bring forth their young. Salmon maytravel a thousand miles or more from the ocean, and,leaping the rapids or other barriers in their way, finallyreach the headwaters of some river where their eggsmay be deposited in safety. Seals migrate with regu-larity to certain islands, where their young are our domesticated Hens, Turkeys, Ducks, and Pea-fowl, if given freedom, will travel a greater or less dis-. Plate XVIII. Page 107. AMERICAN , 23-00 inches. Upper parts brownish black ; nape and under partswhite ; breast marked with grayish brown. ORIGIN OF MIGRATION. 59 tance in search of a place where they may conceal theirnests. Many species of tropical sea birds resort each year tosome rocky islet, situated perhaps in the heart of theirrange, where they may nest in safety. This is not migra-tion as we understand tlie word; but, nevertheless, theobject is the same as that which prompts a Plover totravel to the arctic regions; moreover, the movement isjust as regular. These sea birds pass their lives in thetropics, their presence or absence in any part of theirrange being largely dependent upon the supply of , as in the case of the Warbler which migrates fromSouth America to Labrador, they are annually affectedby an impulse which urges them to hasten to a certainplace. This impulse is periodic, and in a sense is co
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