BIRD MIGRATION. 25 



States along 800 miles of the Gulf coast from western Florida to 

 central Texas. 



The case of the bobolink is typical of many species nesting in 

 North America and wintering entirely in South America (see fig. 

 1). The summer home extends from Cape Breton Island to Sas- 

 katchewan, 2,300 miles, and the migration lines converge toward 

 southeastern United States and then strike directly across the West 

 Indies for South America. In this part of then journey the migration 

 path contracts to an east and west breadth of about 800 miles, and 

 a very large percentage of the birds restrict themselves to the eastern 

 half of it. In South America the region occupied during the winter 

 has about one-fifth the breadth and one-third the area of the breeding 

 range. 



The route of the scarlet tanager is an extreme example of narrow- 

 ness of the path traveled twice a year between winter and summer 

 homes (see fig. 14). The breeding range extends 1,900 miles from 

 New Brunswick to Saskatchewan. The migration range is con- 

 tracted to 800 miles from Florida to Texas as the birds leave the 

 United States. The migration lines continue to converge until in 

 southern Central America the limits are not more than 100 miles 



apart. 



SLOW AND RAPID MIGRATION. 



The black-and-white warbler presents some interesting phases of 

 migration. It winters in Central America, Mexico, the West Indies, 

 and the peninsula of Florida (see fig. 15). Ordinarily it would not 

 be possible to distinguish the spring migrants in Florida from the 

 wintering birds, and the advance of migration could not be noted 

 until the migrants had passed north of the winter range, but records 

 of black-and-white w r arblers striking lighthouses of southern Florida 

 indicate the beginning of the birds' northward migration flight from 

 Cuba. This occurs on the average on March 4, and the birds do not 

 appear in southern Georgia beyond their winter range on the average 

 until March 24. Thus a period of 20 days is taken for the van of 

 migration to move 400 miles across Florida, an average rate of 20 

 miles per day. This rate is about the slowest of all North American 

 birds and is only slightly increased throughout the whole spring 

 migration up the Atlantic coast to Nova Scotia (see Hg. 16), where 

 the birds arrive about May 20, having averaged less than 25 miles a 

 day for the whole 77 days after leaving Cuba. 



Migration along the western border of the range is fully as slow as 

 along the Atlantic coast; on the average, the first arrive at Kerrville, 

 Tex., March 9 and in northern North Dakota May 10, having trav- 

 eled 1,300 miles in 60 days, or 22 miles a day. Thence the speed is 

 more than doubled to the northwestern limit of the range in the 

 Mackenzie Valley. (See fig. 16.) 



