The scarlet tanager presents another extreme case of a narrowly converging migration route starting from its 1,900-mile-wide breeding range in the eastern deciduous forest between New Brunswick and Saskatchewan (Fig. 15). As the birds move southward in the fall, their path of migration becomes more and more constricted, until, at the time they leave the United States, all are included in the 600-mile belt from eastern Texas to the Florida peninsula. The boundaries continue to converge through Honduras and Costa Rica where they are not more than 100 miles apart. The species winters in the heavily forested areas of northwestern South America including parts of Colombia, Ecuador, and Peru. [Illustration: _Figure 16. Distribution and migration of the rose-breasted grosbeak. Though the width of the breeding range is about 2,500 miles, the migratory lines converge until the boundaries are only about 1,000 miles apart when the birds leave the United States._] The rose-breasted grosbeak also leaves the United States through the 600-mile stretch from eastern Texas to Apalachicola Bay, but thereafter as this grosbeak crosses the Gulf of Mexico and enters the northern part of its winter quarters in southern Mexico the lines do not further converge. However, the pathway of those individuals that continue on to South America is considerably constricted by the narrowing of the land through Central America to Panama (Fig. 16). Although the cases cited represent extremes of convergence, a narrowing of the migratory path is the rule to a greater or lesser degree for the majority of North American birds. Both the shape of the continent and major habitat belts tend to constrict southward movement so that the width of the migration route in the latitude of the Gulf of Mexico is usually much less than in the breeding territory. The American redstart represents a case of a wide migration route, but even in the southern United States, this is still much narrower than the breeding range (Fig. 17). These birds, however, cross all of the Gulf of Mexico and pass from Florida to Cuba and Haiti by way of the Bahamas, so here their route is about 2,500 miles wide. [Illustration: _Figure 17. Distribution and migration of the redstart. An example of a wide migration route, birds of this species cross all parts of the Gulf of Mexico, or may travel from Florida to Cuba and through the Bahamas. Their route has an east-and-west width of more than 2,000 miles._] Principal Routes From North America W. W. Cook presented seven of the more important generalized routes for birds leaving the United States on their way to various wintering grounds (1915a; Fig. 18). When migrants return northward in the spring, they may follow these same routes, but it is not known for certain whether they do. These routes are discussed in the following sections.