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2. Winter residents. This class includes those species that 

 summer to the north and winter only less far north. Exam- 

 ples: white-throated sparrow and junco or snowliird. 



3. Summer residents of any place comprise those species 

 that nest at the place and winter southward. Examples : 

 song-thrush, bobolink. 



4. Transients. These are species that pause at a place only 

 while passing from their nesting-place in the North to their 

 winter home in the South, or which tarry a few days on their 

 northward journey. Examples : great blue heron, fox- 

 sparrow, black-poll warbler. 



Migration Routes. — The nesting area of any of the migra- 

 tory species has the form of a band extending east and west a 

 certain distance along the continent. From this zone during the 

 fall migrating period the l)irds move southward along the 

 meridians, and as they do so the lines of migration gradually 

 converge, corresponding to the narrowing of the continent. 

 Consecjuently, there is a crowding along certain hues, such as 

 the seashore and river-courses. Thus the birds that follow 

 down the streams of the Middle West become concentrated into 

 a narrow migration route when they all reach the lowlands of 

 the Mississippi River. Some species pass south of the southern 

 boundary of the United States, and a number e^'cn reach the 

 mainland of South America. Thus the redstart, one of the 

 commonest of our " wood-warblers," reaches Colombia, 

 Venezuela, British Guiana, and Ecuador. In passing from 

 southeastern United States to South America, birds take 

 various routes. Some go by the Antilh^s, and others fly 

 across the Gulf of Mexico to Yucatan. The Antillan 

 route has two main paths, one by the Bahamas and one 

 by Cuba. 



