The black-and-white warbler (_Mniotilta 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 Florida, the West Indies, central Mexico, Central America, and northwestern South America. In the southern part of its breeding range it is nesting in April, but the summer residents of New Brunswick do not reach their breeding grounds before the middle of May. Therefore, about 50 days are required for these northbound birds to cross the breeding range, and if 60 days be allowed for nest building, egg laying, incubation, care of the young, and molt, they would not be ready to start southward before the middle of July (fig. 3). Then another 50-day trip south, and the earliest migrants from the northern areas would reach the Gulf coast in September. But both adults and young have been observed at Key West, Fla., by the middle of July, and on the northern coast of South America by August 21. Since the birds at Key West were fully 500 miles south of the breeding-range, it is evident that they must have come from the southern part of the nesting area. [Illustration: B4504M Figure 3.--Isochronal migration lines of the black-and-white warbler, showing a slow and uniform migration, the advance across the United States being apparently only about 20 miles a day.] Many similar cases might be mentioned, such as the black-throated blue warblers (_Dendroica caerulescens_), which are still observed in the mountains of Haiti in the middle of May when others of the species are en route through North Carolina to breeding territory in New England or have even reached that region. Redstarts (_Setophaga ruticilla_) and yellow warblers (_D. aestiva_), evidently the more southern breeders in each case, 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. [Illustartion: B2282M Figure 4.--The Kentucky warbler, a night migrant, in traveling to its winter quarters in Central America and northwestern South America, uses route no. 5, figure 20.] NOCTURNAL AND DIUNAL MIGRATION