THE MIGRATION OF NORTH AMERICAN BIRDS ) 
tudinal breeding range and a normal migration, the individuais that 
nest farthest south migrate first in fall and proceed to the southern 
“Zy 2 
BREEDING RANGE 
WINTER HOME 
B4503M 
FIGURE 2.—Summer and winter homes of the black-and-white warbler. A very slow migrant, as the 
birds nesting in the northern part of the country take 50 days to cross the breeding range. The rapidity 
of their advance is shown in figure 3. 
these remain farthest north during the winter. In other words, this 
theory supposes that the southward movement of the species is 
normally such that the different groups maintain their relative 
latitudinal positions, both spring and fall. 
The black-and-white warbler (Wniotilta varia) furnishes an example. 
The breeding range of this bird extends west and northwest from 
South Carolina and New Brunswick as far as Great Bear Lake in 
northwestern Canada (fig. 2). The bird spends the winter in southern 
134984°— 359 
