xiv BIRDS OF AMERICA 



territory. The extent to which migration routes contract varies greatly with different 

 species. The Redstart represents one extreme where the Hnes of migration are carried far 

 eastward to include the Bahamas and the Antilles, while they also extend southward into 

 Mexico. Thus the migrating hosts present a broad front with an east and west extension 

 of 2,500 miles from Mexico to the Lesser Antilles. 



The opposite extreme, a narrow migration route, appears in the case of the Rose-breasted 

 Grosbeak. The breeding range extends from Nova Scotia to central Alberta, 2,500 miles, 

 and the migration lines converge until the Grosbeaks leave the United 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 win- 

 tering entirely in South America. The summer home extends from Cape Breton Island to 

 Saskatchewan, 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 

 their 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 narrowness of the path traveled 

 twice a year between winter and summer homes. The breeding range extends i,goo miles 

 from New Brunswick to Saskatchewan. The migration range is contracted 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. 



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. 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 Warblers 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, 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 traveled 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. 



Incidentally it may be remarked that the Black and White Warbler is one of the very 

 few migrants which arrive in Texas and Florida before they appear at the mouth of the 

 Mississippi. The van of most species reaches southern Louisiana earlier than southern Texas. 



The Cliff Swallow is another species with a slow migration schedule. It must start 

 northward very early, since by March 10 it is already 2,500 miles from the winter home and 

 yet averages only 25 miles a day for the next 20 days while rounding the western end of the 

 Gulf of Mexico. It more than doubles this rate while passing up the Mississippi and Ohio 

 River valleys. The crossing of the Allegheny Mountains comes next, and there are only 200 

 miles of progress to show for the 10 days' flight. By this time spring has really come east of 

 the AUeghenies, and the Swallow travels 60 miles a day to its summer home in Nova Scotia. 

 It is to be noted that the Swallow works up to high rates of speed only when it is traveling 

 on the diagonal, and that except during the ten days spent in crossing the mountains each 

 ID days' travel covers approximately 5 degrees of latitude. 



