EXTENT OF MIGRATION 41 



the journeys of those birds that leave the United States are far more 

 extended than those performed by the birds of the western portion of 

 the continent. 



Of our thirty-nine species of Warblers, twenty-seven winter en- 

 tirely south of the United States, twenty of them reaching South Amer- 

 ica, the Yellow Warbler and Blackpoll having been recorded from as 

 far south as Peru. The shortest journey of any Blackpoll, as Cooke 

 points out, is 3,500 miles, " while those that nest in Alaska have 7,000 

 miles to travel to their probable winter home in Brazil." (" Warblers 

 of North America," p. 15; see also his admirable " Distribution and 

 Migration of Warblers," Bull. No. 18, Biological Survey.) 



Of our ten species of Flycatchers, nine leave the United States for 

 the winter (the Crested Flycatcher is of rare occurrence in southern 

 Florida at this season), and all of them reach South America, the 

 Kingbird (Tyrannus tyrannus) going as far south as Bolivia. 



Two of our eight Vireos remain in Florida during the winter, five 

 winter in Central America, and one, the Red-eye, extends its winter 

 journey to Bolivia and southwestern Brazil. 



Even more extended migrations are performed by certain Sand- 

 pipers and Plovers which nest within the Arctic Circle and winter 

 as far south as the southern extremity of South America. 



Routes of Migration. Lying within those regions climatically most 

 favorable for the human race, the boundaries of the summer ranges 

 of most of our migrating birds are known with more or less definiteness; 

 but when they leave the temperate zone to enter tropical wilds, our 

 knowledge of their distribution is far less satisfactory. The data now 

 available show, however, that a field of exceptional interest awaits 

 the investigator who, with adequate information, traces the routes 

 of migration followed by birds in journeying between their summer and 

 winter homes. 



In Eastern North America some migrant land birds leave the 

 United States by passing through Texas into Mexico and are unknown 

 in the southeastern Atlantic States .(e. g. the Mourning Warbler) ; 

 others leave through Florida and are unknown in Texas and Mexico 

 (e.g. the Bobolink and Blackpoll Warbler). Others still (e.g. the 

 Redstart), travel through both Texas and Florida into Mexico as well 

 as to the West Indies. There is also a route which appears to cross the 

 Gulf of Mexico from the region at the mouth of the Mississippi, though 

 no species is confined to it. 



It was at one time supposed that the birds which left the United 

 States by way of Florida all crossed directly to Cuba, but, according 

 to Cooke ('03), "The main traveled highway is that which stretches 

 from northwestern Florida across the Gulf, continuing the southwest 

 direction which most of the birds of the Atlantic Coast follow in passing 

 to Florida. A larger or smaller proportion of nearly all the species 

 bound for South America take this roundabout course, quite regardless 

 of the 700-mile flight over the Gulf of Mexico." 



