tions of migratory birds adhere with more or less fidehty to their re- 

 spective flyways. The terms "flyway" and "migration route" have in 

 the past been used more or less as synonyms but the modern concept 

 of a flyw^ay is that it is a vast geographic region with extensive breeding 

 grounds and wintering grounds connected with each other by a more 

 or less complicated system of migration routes. Each flyway has its 

 own populations of birds, even of those species that may have a con- 

 tinental distribution. The breeding grounds of one or more flyways 

 may (and usually do) overlap broadly, so that during the nesting 

 season extensive areas may be occupied by birds of the same species but 

 which belong to different flyways. 



The maps (figs. 13, 14, 15, and 16) show the flyways as they are now 

 understood. It should be pointed out, however, that in the other maps 

 used in this bulletin, the entire range of a species is shown without 

 any attempt to distinguish by flyways the different populations. As 

 banding data accumulate for the nongame species, this distinction will 

 ultimately be possible, but for the time being, consideration of their 

 migrations must be chiefly by routes. 



The following discussion of the principal routes of North American 

 birds relates chiefly to the fall migration, for, except as otherwise noted, 

 the spring flight generally retraces the same course. The routes indi- 

 cated on the map (fig. 17) must not be considered as representing paths 

 with clearly defined borders, but rather as convenient subdivisions of 

 the four great flyways that, as indicated above, cover practically the 

 entire width of the North American Continent and extend from the 

 Arctic coast to South America. 



Atlantic oceanic route 



By reference to figure 17 it will be noted that route No. i is almost 

 entirely oceanic, passing directly over the Atlantic Ocean from Labra- 

 dor and Nova Scotia to the Lesser Antilles, and then through this group 

 of small islands to the mainland of South America. This is not a 

 popular route and its chief claim to fame is that it is the fall route 

 used by most of the adult eastern golden plovers, and probably by some 

 other shore birds. Since it lies entirely over the sea, this route is defi- 

 nitely known only at its terminals and from occasional observations 

 made on Bermuda and other islands in its course. Some of the shore 

 birds that breed on the Arctic tundra of Mackenzie and Alaska fly 

 southeastward across Canada to the Atlantic coast and finally follow this 



48 



