CHAPTER TEN 



MIGRATION OF BIRDS 



Swift overhead the small birds pass, 

 With cries that are lonely and sweet and clear. 



CELIA THAXTER 



FOR many years the Biological Survey of the United 

 States Department of Agriculture has received reports 

 from observers in different parts of the country, giving 

 for each bird the date in spring when it was first noticed, 

 when it became common, and when the last individuals 

 were seen. These reports, supplemented by those of 

 travelers and residents in other parts of the Western 

 Hemisphere, have afforded much information about the 

 movements of American birds. 



Bird migrations. None of our common birds nest at 

 the southern end of their migration range. They may 

 go to Mexico or South America for the winter, but the 

 North is where they rear their young. When the proper 

 season comes, they have an impulse to start for their 

 breeding places. Those birds* which do not arrive at 

 their Northern home until late in April or in May, when 

 the weather is usually more settled than in March, may 

 be expected at nearly the same time each year. Those 

 kinds that arrive early in the spring sometimes make the 

 mistake of coming North just before a severe storm or a 

 spell of cold weather. Birds cannot foretell the weather 

 any better than we can, but they are influenced by con- 

 ditions that prevail where they are at a given time. 



How birds find their way has long been a mystery. To 

 some extent they follow river valleys or coast lines, 'but 

 this fact does not fully explain the return of a bird, after 



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