MIGRATIONS OF ANIMALS 481 



food, shelter from enemies, and favorable climatic con- 

 ditions. 



Migrations of Animals. — In the discussion of the 

 distribution of animals it has been assumed that each 

 species is confined to a fairly definite area; but, while 

 in general this is true, shad and smelt migrate from 

 the sea to lay their eggs in fresh water; certain species 

 of eels leave fresh water to deposit their eggs in 

 the sea; many other species of fishes migrate from deep 

 water into shallow water at the breeding season. The 

 reindeer, musk-ox, bison, certain species of hares, rats, 

 and many other animals may journey widely from one 

 region to another chiefly in search of food. 



The birds, however, afford the most striking examples 

 of extended migrations whose impelling cause remains 

 an unsettled question. Practically all the insect-eating 

 species of temperate and cold regions spend their 

 winters in warmer climates, the shore birds, such as 

 the sandpipers, plovers and phalaropes, traveling at 

 least one thousand miles. The golden plover, nesting 

 in the neighborhood of the Arctic Circle in North 

 America, flies southward to Nova Scotia, and thence by 

 a direct flight of twenty-five hundred miles reaches South 

 America where it winters in Argentina. It is a further 

 remarkable fact that in completing its round trip of 

 seven thousand miles it returns north by way of Texas. 

 A few Alaskan shore birds winter in the Hawaiian 

 Islands two thousand miles distant; a Siberian swallow 

 winters in Mexico or Burmah; the European swallow 

 migrates to Africa; and there are hosts of other species 

 whose journey ings are as remarkable and as difficult to 

 comprehend. 



