THE MIGRATION OF NORTH AMERICAN BIRDS ae 
100 miles apart. The species winters in northwestern South America, 
where it spreads out over most of Colombia, Ecuador, and Peru. 
The rose-breasted grosbeak also leaves the United States through 
the 700-mile stretch from eastern Texas to Appalachicola Bay, but 
thereafter the lines do not further converge, as this grosbeak enters the 
northern part of its winter quarters in Central America and South 
America through a door of about the same width (fig. 18). 
ANS 6 REED NG _RANGE 
WA WINTER HOME 
~-~- EAST AND WEST LIMITS 
OF MIGRATION ROUTE 
B4501M 
FIGURE 18.—Distribution and migration of the rose-breasted grosbeak. ‘Though the width of the breeding 
rangeis about 2,500 miles, the migratory lines converge until the boundaries are only about 700 miles apart 
when the birds leave the United States. For migration paths of other widths see figures 16, 17, and 19. 
While the cases cited represent extremes of convergence, a narrow- 
ing of the migratory path is the rule to a greater or less degree for the © 
majority of North American birds. The shape of the continent tends 
to effect this, and so the width of the migration route in the latitude 
of the Gulf of Mexico is usually much less than in the breeding 
territory. 
