THE MIGRATION OF NORTH AMERICAN BIRDS 53 
west to the Pacific coast in British Columbia (fig. 27). It seems 
evident that this 1s a range extension that has taken place compara- 
tively recently by a westward movement from the upper Missouri 
x 
: SA 
Ne 
De 
aerew S 
= \\\ \» 
\\ 
AW BREEDING RANGE 
| ZZ winter Home - 
eee SAS AND WEST LIMES. 
OF MIGRATION ROUTE 
B4506M 
FIGURE 27.—Distribution and migration of the red-eyed vireo. It is evident that the red-eyed vireo has 
only recently invaded Washington by an extension of its breeding range almost due west from the upper 
Missouri Valley. Like the bobolink, however (fig. 23), the western breeders do not take the short cut 
south or southeast from their nesting grounds, but migrate spring and fall along the route traversed in 
making this extension. 
Valley, and that the invaders retrace in spring and fall the general 
route by which they originally entered the country. 
In the case of the bobolink, a new extension of the breeding range, 
and a consequent change in the migration of the species, has taken 
place since the spread of settlement in this country (fig. 23). A bird 
