THE BIRDS' AIR LINE 



of our country. Some of them only travel from 

 the higher parts of the Rocky Mountains or 

 Sierras, where they nest, to the low, warm valleys 

 in which they winter. 



Those that leave the United States go into 

 Mexico. Some continue their journey as far 

 south as Guatemala, but few go farther. They 

 all travel overland, and do not therefore en- 

 counter the dangers to which many of our east- 

 ern migrants are exposed. 



It is surprising that most of the bird travelers 

 of Alaska migrate to the eastern United States. 

 Some of them actually go to their winter homes 

 by way of Florida and the West Indies! But 

 when we examine a map we find that a large 

 part of Alaska is east of the Rocky Mountain 

 system. These mountains, like a great wall, have 

 prevented the western birds from crossing to 

 their eastern side; while the bird pioneers from 

 the East have found nothing to prevent them 

 from taking up fresh claims until they reached 

 this same great wall in the far Northwest. So 

 far as birds are concerned, therefore, Alaska is 

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