34 BIRDS OF SOUTH DAKOTA 



BIRD MIGRATION 



We who live in the Northern Hemisphere are peculiarly 

 fortunate in the privilege we have of viewing a bird procession 

 twice a year that spreads over the whole of North America to 

 nest. Mr. Wells W. Cooke says, "South America has almost no 

 migratory land birds, for bleak Patagonia and Tierra del Fuego 

 offer no inducements to these dwellers of the limitless forests 

 of the Amazon." (Department of Agriculture, Bulletin No. 

 185, p. 4.) 



There are four classes of birds with respect to migration : 

 (1) permanent residents ; those that do not migrate ; (2) summer 

 residents; those that come to us from the south in spring and 

 return in the autumn; (3) winter residents; those that come to 

 us from the north in the autumn and return in spring ; (4) tran- 

 sients, or migrants; those that pass through our State on their 

 way north in spring and again when they return south in au- 

 tumn. 



The general direction of bird migration is north and 

 south, but with many species this direction may swing at times 

 to east and west. Many Snipes and Plovers, for example, which 

 spend the winter in South America, come north across the Gulf 

 of Mexico, then up the Mississippi Valley, and nest in the in- 

 terior of North America. In the autumn they take an easterly 

 course to the Atlantic coast, thence south to their wintering 

 place. The Bobolinks that nest in the northwest go to their win- 

 ter home in South America by the roundabout way of Florida, 

 and the Connecticut "Warblers come north through the interior 

 of the United States and return south along the Atlantic coast. 



The reason for these circuitous routes is not well under- 

 stood. Generally speaking, birds migrating follow "mountain 

 chains, coast lines and particularly river valleys," but there are 

 so many exceptions that other causes evidently enter into the 

 problem. At present in South Dakota many birds are extending 

 their range westward with the growth of trees. These birds will 

 follow the migrating routes by which they come, returning 

 first east and then south. Many birds follow such a route be- 

 cause their range has been extended in this way. 



