THE MIGRATION OF BIRDS 



average. Individuals will at times pause and re- 

 main for a few days in a favourable locality before 

 proceeding farther. When large bodies of water 

 are encountered longer flights are of course necessary, 

 for land birds cannot rest on the water as their 

 feathers would soon become water-soaked and 

 drowning would result. Multitudes of small birds, 

 including even the little Ruby-throated Humming- 

 bird, annually cross the Gulf of Mexico at a single 

 flight. This necessitates a continuous journey of 

 from five hundred to seven hundred miles. Some 

 North American birds migrate southward only a few 

 hundred miles to pass the winter, while many others 

 go from Canada and the United States to Mexico, 

 Central and South America. 



The ponds and sloughs of all that vast country 

 lying between the Great Lakes and Hudson Bay on 

 the east and the mountains of the Far West, con- 

 stitute the principal nursery of North American 

 waterfowl, whence, in autumn, come the flocks of 

 Ducks and Geese that in winter darken the Southern 

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