viii BIRDS OF AMERICA 



If migration were a steady movement northward with the same individuals always in the 

 van, numerous careful observations might make it possible to approximate the truth; but 

 instead of this, most migrations are performed somewhat after the manner of a game of 

 leap-frog. The van in spring migration is composed chiefly of old birds, and as they reach 

 their nesting places of the previous year they remain to breed. Thus the vanguard is con- 

 stantly dropping out and the forward movement must depend upon the arrival of the next 

 corps, which may be near at hand or far in the rear. Moreover, in our present state of knowl- 

 edge we can not say whether a given group of birds after a night's migration keeps in the 

 van on succeeding nights or rests and feeds for several days and allows other groups pre- 

 viously in the rear to assume the lead. It is known that birds do not as a rule move rapidly 

 when migrating in the daytime, but from the meagre data available it may be inferred that 

 the speed at night is considerably greater. During day migration the smaller land birds 

 rarely fly faster than 20 miles an hour, though the larger birds, as Cranes, Geese, and Ducks 

 move somewhat more rapidly. The result of timing Nighthawks on several occasions gave 

 a rate of 10 to 14 miles an hour, the former being the more usual speed. This slow rate results 

 from the irregularity of the flight, caused by the birds' capturing their evening and morning 

 meals en route. In the evening the flight lasted about an hour and a half and in the morning 

 about an hour. Thus a distance of approximately j,o miles would be traveled by each indi- 

 vidual during the morning and evening flights. 



Night migrants probably average longer distances in most of their flights, and this is 

 known to be the case with some species. The Purple Martin, during the spring of 1884, 

 performed almost its entire migration from New Orleans to Lake Winnipeg during only 12 

 nights — an average of 120 miles for each night of movement — and some late migrants, 

 like the Gray-cheeked Thrush, must make still greater distances at a single flight. That 

 most of them can fly several hundred miles without stopping is proved by the fact that they 

 make flights of 500 to 700 miles across the Gulf of Mexico. 



The length of the migration journey varies enormously. A few birds, like the Grouse, 

 Quail, Cardinal, and Carolina Wren, are non-migrator>'. Many a Bobwhite rounds out its 

 full period of existence without ever going 10 miles from the nest where it was hatched. 

 Some other species migrate so short a distance that the movement is scarcely noticeable. 

 Thus, Meadowlarks are found near New York City all the year, but probably the individuals 

 nesting in that region pass a little farther south for the winter and their places are taken by 

 migrants from farther north. Or part of a species may migrate and the rest remain sta- 

 tionary, as in the case of the Pine Warbler and the Black-headed Grosbeak, which do not 

 venture in winter south of the breeding range. With them fall migration is only a with- 

 drawal from the northern and a concentration in the southern part of the summer home — 

 the Warbler in about a fourth and the Grosbeak in less than an eighth of the summer area. 

 In the case of the Maryland Yellow-throat, the breeding birds of Florida are strictly non- 

 migratory, while in spring and fall other Yellow-throats pass through Florida in their journeys 

 between their winter home in Cuba and their summer home in New England. 



Another variation is illustrated by the Robin, which occurs in the middle districts of 

 the United States throughout the year, in Canada only in summer, and along the Gulf of 

 Mexico only in winter. Probably no individual Robin is a continuous resident in any sec- 

 tion; but the Robin that nests, let us say, in southern Missouri, spends the winter near the 

 Gulf, while his hardy Canada-bred cousin is the winter tenant of the abandoned summer 

 home of the southern bird. 



Most migratory birds desert the entire region occupied in summer for some other dis- 

 trict adopted as a winter home. These two homes are separated by very variable distances. 

 Many species from Canada winter in the United States, as the Tree Sparrow, Junco, and 

 Snow Bunting; 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. 



