With our present knowledge of bird migration it is difficult at best 

 to recognize distinct broad belts of migration down the North 

 American continent encompassing groups of distinct populations or 

 species. It seems that so much intermingling of populations occurs 

 that distinctions between broad "flyway" belts are not discernible. 

 About all we can say for sure now is that birds travel between certain 

 breeding areas in the North and certain wintering areas in the South 

 and that a few heavily traveled corridors used by certain species, and 

 more generalized routes followed by one or more species, have 

 become obvious. 



Narrow Routes 



Some species exhibit extremely narrow routes of travel. The red 

 knot and purple sandpiper, for example, are normally found only 

 along the coasts because they are limited on one side by the broad 

 waters of the ocean, and on the other by land and fresh water; neither 

 of these habitats furnish conditions attractive to these species. 



The Ipswich race of the savannah sparrow likewise has a very 

 restricted migration range. It is known to breed only on tiny Sable 

 Island, Nova Scotia, and it winters from that island south along the 

 Atlantic coast to Georgia. It is rarely more than a quarter of a mile 

 from the outer beach and is entirely at home among the sand dunes 

 with their sparse covering of coarse grass. 



The Harris' sparrow supplies an interesting example of a 

 moderately narrow migration route in the interior of the country 

 (Fig. 14). This fine, large sparrow is known to breed only in the 

 narrow belt of stunted timber and brush at or near the limit of trees 

 from the vicinity of Churchill, Manitoba, on the west shore of Hudson 

 Bay, to the Mackenzie Delta 1,600 miles to the northwest. When this 

 sparrow reaches the United States on its southward migration, it is 

 most numerous in a belt about 500 miles wide, between Montana 

 and central Minnesota and continues south through a relatively 

 narrow path in the central part of the continent. Knowledge of 

 habitat preference by Harris' sparrows suggests the narrow 

 migration range is restricted to the transition between woodland and 

 prairie, a type of habitat approaching the woodland-tundra 

 transition of its breeding area. Development of this migration route, 

 of course, preceded destruction of the heavy eastern forests by 

 colonists from Europe. Its winter range lies primarily in similar 

 country extending from southeastern Nebraska and northwestern 

 Missouri, across eastern Kansas and Oklahoma and through a 

 narrow section of eastern Texas, at places hardly more than 150 miles 

 wide. 



Converging Routes 



When birds start their southward migration the movement 

 necessarily involves the full width of the breeding range. Later, in the 

 case of landbirds with extensive breeding ranges, there is a 

 convergence of the lines of flight taken by individual birds owing, in 



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