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Figure 1.—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 speed of migration is shown in figure 2. (ssss1)

Figure 2.—Isochronal migration lines of the black and white warbler, showing a very slow and uniform migration. These birds apparently advance only about 20 miles a day in crossing the United States. (ssss1)

Many similar cases might be mentioned, such as the black-throated blue warblers, which are still observed in the mountains of Haiti in the middle of May, when others of this species are en route through North Carolina to breeding territory in New England or have even reached that region. Redstarts and yellow warblers, evidently the more southern breeders, are seen returning southward on the northern coast of South America just about the time that the earliest of those breeding in the North reach Florida on their way to winter quarters.