Distribution and Migration 



All bii'ds are at home during the breeding season, which usually 

 covers the latter part of spring and early summer. At other times of 

 year they wander more or less from this breeding area. In some 

 species this wandering or migration is irregular, varying in extent in 

 different seasons according to the scarcity or abundance of the food- 

 supply. In othors it has become a definite movement southward in 

 autumn and northward in spring, the apparent result of an hereditary 

 tendency, which may have been acquired at the time when our present 

 seasonal climatic changes originated. Some of these migrations 

 extend over thousands of miles, so that certain of our summer birds 

 of the Northern United States pass the winter in the tropics of South 

 America, while some of the Plover and Sandpipers which breed within 

 the Arctic circle winter in the Argentine Eepublic or Chili. 



The movements of the migrating birds are often very regular from 

 year to year, so that it is possible to predict within a few days when a 

 given species of bird will arrive — at least, when the bulk or norinal 

 flight will arrive. There are, of course, occasional stragglers which 

 come exceptionally early. 



The way in which birds perform their extended migrations is a 

 matter of great interest, and one concerning which we have still much 

 to learn. We know that there are two classes of migrants, (1) those 

 that fly by day, and (2) those that fly by night. The former comprise 

 most of the birds which habitually associate in compact flocks, such as 

 Doves. Horned Larks, Crows, Jays, Grackles, Blackbirds, Cedarbirds, 

 Titlarks, Eobins and Bluebirds; also. Hawks, Swallows, Swifts, Night 

 Hawks and Hummingbirds. The night migrants comprise all our 

 more delicate woodland birds. Thrushes, Warblers, Vireos, Tanagers, 

 Wrens, etc., as well as Kail, Woodcock, Bittern and some Snipe. 



It is probable that all birds have a remarkably developed sense of 

 direction, such as we see in the Carrier Pigeon, which enables them to 

 retrace a route over which they have once passed. Then, too, the 

 prominent features of the landscape may serve as a guide to the 



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