In retracing their course to reach the western edge of the route followed 

 by the bulk of the bobolinks that breed in the northern United States 

 and southern Canada, these western pioneers must fly long distances 

 along a line that runs almost due east and west. 



Similarly it is possible to sketch what seems to be the logical evolution 

 of the remarkable routes of the golden plover (fig. i8). It may be 

 assumed that the eastern birds of this species first followed an all-land 

 route from the South American winter quarters through Central 

 America, Mexico, and Texas to the western parts of the Mississippi 

 Valley. As the migration route lengthened northward with the re- 

 treat of the ice and the bird's powers of flight developed, there would 

 be a tendency to straighten the line and to shorten it by cutting off 

 some of the great curve through Mexico and Texas. First a short 

 flight across the western part of the Gulf of Mexico was probably 

 essayed. Proving successful, this was followed by flight lines that 

 moved farther east, until finally the roundabout curve through Texas 

 was entirely discarded and the flight made directly across the Gulf 

 to southern Louisiana. 



As the great areas in Canada were gradually added to the birds' 

 domain, other important factors arose, the chief being the attractive- 

 ness of the vast stretches of coast and plain of the Labrador Peninsula, 

 which in fall offered a bountiful store of berries. The fall route there- 

 fore worked eastward to the Gulf of St. Lawrence, thence southwest 

 along the coast to Florida and across the Gulf of Mexico to the Central 

 American mainland. A series of shortening flights followed to take 

 out the great curve of the Atlantic coast. A relatively short ocean 

 flight was probably attempted, say from Cape Cod to the Bahama 

 Islands, Cuba, and Jamaica, followed eventually by the long direct 

 oceanic route as it is now known. 



As the Labrador Peninsula in spring is bound by frost and shrouded 

 in fog while the season advances rapidly through the interior, the 

 oceanic route proved useful only in fall, and the spring flight continued 

 through the Mississippi Valley. This outline, although entirely hypo- 

 thetical, gives a probable and fairly plausible explanation of the origin 

 of this wonderful route, particularly when it is remembered that mi- 

 gration routes as now known are evolutions — age-long modifications 

 of other routes. 



The evolution of the migration route of the Pacific golden plover 

 may be explained in a similar fashion. At first the route probably 



71 



