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Figure 1. Summer and winter homes of the black-and-white warbler. A very slow migrant, these birds nesting in the northern part of the country take 50 days to cross the breeding range. The speed of migration is shown in Fig. 2.

Many similar cases might be mentioned, such as the black-throated blue warblers still observed in the mountains of Haiti during the middle of May when others of this species are en route through North Carolina to New England breeding grounds. Redstarts and yellow warblers, evidently the more southern breeders, are seen returning southward on the northern coast of South America just about the time the earliest of those breeding in the North reach Florida on their way to winter quarters. Examples of the Alaska race of the yellow warbler have been collected in Mississippi, Florida, and the District of Columbia as late as October.

Figure 2. Isochronal migration lines of the black-and-white warbler, showing a very slow and uniform migration. The solid lines connect places at which these birds arrive at the same time. These birds apparently advance only about 20 miles per day in crossing the United States.