BIRD MIGRATION 9 



are separated by very variable distances. Many species from Canada 

 winter in the United States, as the tree sparrow, juneo, and snow/lake; 

 others nesting in northern United States winter in the Gulf States, 

 as the chipping, field, Savannah, and vesper sparrows, while more 

 than a hundred species leave the United States for the winter and 

 spend that season in Central or even in South America. Nor are they 

 content with journeying to northern South America, but many cross 

 the Equator and pass on to the pampas of Argentina and a few even 

 to Patagonia. Among these long-distance migrants are some of our 

 commonest birds; the scarlet tanagcr (PL IV) migrates from Canada 

 to Peru; the bobolinks (fig. 1 and PI. I) that nest in New England 

 probably winter in Brazil, as do purple martins, cliff swallows, barn 

 swallows, nighthawks, and some thrushes, which are their companions 

 both summer and whiter. The black-poll warblers that nest in Alaska 

 whiter in northern South America, at least 5,000 miles from the 

 summer home. The land bird with the longest migration route is 

 probably the nighthawk, which occurs north to Yukon and south, 

 7,000 miles away, to Argentina. 



But even these distances are surpassed by some of the water birds, 

 and notably by some of the shorebirds, which as a group have the 

 longest migration routes of any birds. Nineteen species of shore- 

 birds breed north of the Arctic Circle, every one of which visits South 

 America in winter, six of them penetrating to Patagonia, a migration 

 route more than 8,000 miles in length. 



The world's migration champion, however, is the arctic tern (fig. 3 

 and PL II). It deserves its title of "arctic," for it nests as far north 

 as land has been discovered ; that is, as far north as the bird can find 

 anything stable on which to construct its nest. Indeed, so arctic 

 are the conditions under which it breeds that the first nest found by 

 man in this region, only 7J° from the pole, contained a downy chick 

 surrounded by a wall of newly fallen snow that had been scooped out 

 of the nest by the parent. When the young are full grown the entire 

 family leaves the Arctic and several months later they are found 

 skirting the edge of the Antarctic continent. 



What their track is over that 11,000 miles of intervening space 

 no one knows. A few scattered individuals have been noted along 

 the United States coast south to Long Island, but the great flocks 

 of thousands and thousands of these terns which range from pole to 

 pole have never been noted by an ornithologist competent to indi- 

 cate their preferred route and their time schedule. The arctic terns 

 arrive in the far north about June 15 and leave about August 25, 

 thus staying 14 weeks at the nesting site. They probably spend a 

 few weeks longer hi the whiter than in the summer home, and this 

 would leave them scarcely 20 weeks for the round trip of 22,000 

 miles. Not less than 150 miles hi a straight line must be their daily 



76048°— Bull. 185—15 2 



