5=^ 



MARCH 20. 

 MARCH 10. 



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. 

 (See p. 13.) 



(fig. 2.). Then another 50-day trip south, and the earHest 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 south- 

 ern part of the nesting area. 



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, Vv^hen 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 



14 



