BIED MIGEATION. 7 



movement northward with the same individuals always in the van, 

 numerous careful observations might make it possible to approximate 

 the tnith; but instead of this, most migrations are performed some- 

 what after the manner of a game of leapfrog. The van m 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 constantly 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 previously 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 meager 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 irregu- 

 larity 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 30 miles would be traveled by each individual dur- 

 ing 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 dis- 

 tances at a single flight. That most of them can fly several hundred 

 miles without stopping is proved by the fact that they make flights 

 (*f 500 to 700 miles across the Gulf of Mexico. 



DISTANCE OF MIGRATION. 



'J"li(! length (j1' the migratioji journey varies enormously. A few 

 birds, like the grouse, quail, cardinal, and Carolina wren are nonmi- 

 gratory. Many a bo})white 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 not ifeablf. Tims, mea(h)whuks fivo found near Ncnv York 

 City uU th(^ y<'ai', hul, piobubly the individuals nc^stiug in that I'egion 

 pass a little further south for the winter and their places are taken by 

 migrants from f;iith(i- tiorth. Oi' pail of a spccIcM may migrate^ and 



