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,” 
