available concerning the extent and times of the seasonal journeys of 

 most of the species. Many gaps, however, still remain in our knowl- 

 edge of the subject. Much has been learned, and present knowledge 

 is being placed on record, but it must be left to future study to clear 

 away many of the uncertainties that continue to make bird migration 

 one of the most fascinating subjects in the science of ornithology. 



Each kind of bird seems to have its own reaction to its environment, 

 so that the character of movement differs widely in the various species, 

 and seldom do any two present the same picture. In fact, bird migra- 

 tion has been described as a phase of geographic distribution wherein 

 there is a more or less regular seasonal shifting of the avian population 

 caused by the same factors that determine the ranges of the sedentary 

 species. If this view is correct, then it must be recognized that the far- 

 reaching works of man in altering the natural condition of the earth's 

 surface can so change the environment necessary for the well-being of 

 the birds as to bring about changes in their yearly travels. The nature 

 and extent of the changes wrought by man on the North American 

 Continent are easily apparent. Forests have been extensively cut away 

 and their places have been taken by second growth or cultivated land, 

 and wide stretches of prairie and plain have been broken up, irrigated, 

 and devoted to agriculture. These great changes are exerting a pro- 

 found effect upon the native bird populations, and the various species 

 may be either benefited or adversely affected thereby. 



The Federal Government has recognized its responsibility to the 

 migratory birds under changing conditions brought about by man, 

 iind by enabling acts for carrying out treaty obligations, it is now giving 

 most species legal protection under regulations administered by the 

 Fish and Wildlife Service. Much is being done by legislation for the 

 welfare of the birds. The effectiveness of these conservation laws, 

 however, is increased in the same measure that the people of the country 

 become acquainted with the facts in the hfe histories of the migrants 

 and interest themselves personally in the well-being of the various 

 species. Long before the white man came to America the birds had 

 established their seasonal lanes of migration throughout the Western 

 Hemisphere. The economic, inspirational, and esthetic values of these 

 migratory species dictate that they be permitted to continue their long- 

 accustomed and still-mysterious habits of migration from clime to 

 clime. 



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