8 KORTH AMERICAN WARBLERS. 



at this season the Swainson warbler {IleUnaia sioauisoni) is restricted 

 to the island of Jamaica, while the yellow warbler {JDendroica destiva 

 and its subspecies) is distributed from western Mexico to French 

 Guiana. 



ROUTES OF MIGRATION. 



In passing between the United States and their winter homes, war- 

 blers use all the routes followed b}^ other species of birds, The belief 

 of the writer is that when birds begin to migrate in the fall, their 

 path of migration is the full width of the breeding range, but that 

 owing to the conformation of the North American continent, the lines 

 of flight taken b}^ individual birds necessarily converge so that as 

 a species proceeds southward, the width of the region occupied by it 

 becomes less. The kingbird {Tyrannus tyrannus) affords a more 

 striking example of this than can be found among the warblers. Its 

 summer home — from Newfoundland to British Columbia — has a width 

 of 2,800 miles; its paths of migration converge until in the southern 

 United States from southern Florida to the mouth of the Rio Grande 

 their total width is 900 miles. Continuino- southward, the eastern edp^e 

 of this path or belt appears to extend from southern Florida to 

 Yucatan, but the western edge is less sharply defined; few individuals 

 of the species seem to travel west of a line drawn from Corpus Christi 

 to Tabasco. Thus in the latitude of southern Yucatan the migration 

 path is scarcely 400 miles wide, and the great bulk of the species prob- 

 abl}^ move in a belt less than half this width. 



When the warblers pass beyond the southern boundary of the United 

 States, the width and destination of their paths of migration var}^ 

 greatly among the different species. Some go to the Bahamas and not 

 to Cuba, others to Cuba and not to Yucatan, or to Yu(;atan and not to 

 Cuba. In the case of wide-ranging species, like the black and white 

 warbler or the redstart, it is probable that some individuals cross from 

 northern Florida to the northern Bahamas, others from centrrl Florida 

 to the central or southern Bahamas, others from southern Florida to 

 Cuba, others from northwestern Florida to Yucatan, and still others 

 from points to the west of these localities. These different lines of 

 flight between the southern boundar}^ of the United States and the 

 countries to the south are called in this publication migration routes, 

 but they are not to be considered definite paths with exact boundaries, 

 but merely minor subdivisions of a great migration route that pass 

 insensibl}" into each other. The principal subdivisions, or routes, are 

 the following: 



1. United States to the Bahamas. 



2. Florida to Cuba. 



3. Western. Florida to Yucatan. 



4. Northern coast of the Gulf of Mexico southward. ' 



5. Texas to' Mexico by land. 



6. AVestern United States to Mexico. ■ 



