BIRD 



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BIRD 



over the roofs of the cities? One day there 

 are no martins to be seen, no warblers to be 

 heard; the next day they seem to be every- 

 where, making themselves as much at home 

 as though they were steady residents and not 

 mere summer tourists settling for a brief 

 sojourn. How far have they flown? Where 

 have they spent the winter? How long did it 

 take them to come back? Why do they mi- 

 grate? These questions and many more are 

 certain to occur to any student of this most 

 fascinating subject. 



Why Birds Migrate. The little sparrows 

 that hop about in the deepest snow of winter 

 and seem to enjoy themselves prove clearly 

 that some birds are not affected by the cold, 

 and careful study has made it practically con- 

 clusive that this is true of all birds. A mocking 

 bird, which everyone is accustomed to think 

 of as a dweller in warm climates, was observed 

 to live happily in New York during an unus- 

 ually cold winter, and frequently bluebirds, 

 looked upon as the surest harbingers of spring, 

 will winter in a northern wood. The condition 

 of residence depends on their food supply. The 

 vagrant mocking bird has found a privet tree; 

 the bluebirds hover near a berry-covered cedar 

 tree. But those birds which feed upon insects 

 or worms would starve if they could not seek 

 their winter food in less severe climates than 

 the temperate zones. There is thus a rough 

 division of birds into those which make long 

 migrations and those which do not, strictly 

 according to the demands of their appetites. 



But the need for food cannot alone account 

 for the marvelous departure of the birds from 

 home. If it did, insect-eating birds would 

 remain the year round in the warm parts of the 

 earth, where the air is full of their prey. 

 Moreover, some of the birds start south .in 

 August, when insect life is still plentiful in the 

 higher latitudes. Behind the great movements 

 there is some primal cause, some strong urge 

 which man cannot comprehend. Scientists 

 explain that ages ago, when climatic conditions 

 were much more extreme, birds were actually 

 forced to migrate by the slowly pushing ice 

 cap which came down from the Pole, crowding 

 out vegetable and animal life before it. As 

 this receded, the birds began to press north- 

 ward from their enforced home, and somehow 

 this planted in them an instinct, a heredity of 

 habit, which resulted in the seasonal migra- 

 tions. However that may be, it is certain that, 

 as spring approaches, something says to cer- 

 tain birds, "Fly northward, and there build 



your nests and rear your young;" and in a few 

 days the northern woods and fields begin to 

 swarm with welcome visitors. Bird-lovers who 

 find the domestic life of the pretty creatures 

 that nest in their yards a source of unceasing 

 interest, report that pairs of birds sometimes 

 return season after season to the same tree 

 or bird house. 



How They Migrate. When they have felt 

 the "mysterious call" the birds respond at once, 

 each species organizing its flight as have its 

 ancestors from time immemorial. Some spe- 

 cies are most systematic; others are more 

 happy-go-lucky, traveling as the spirit moves, 

 and covering no great distance at a time. Al- 

 most invariably, however, there is a certain 

 order. The old males, strong of wing, fly 

 first, next come the females, and at the close 

 of the procession the young birds, who are 

 re-visiting their northern birthplace for the 

 first time. Perhaps as they advance northward 

 they may find that they have started a little 

 too soon. Then they slacken their pace, and 

 tarry in the intermediate regions for a time. 

 Some kinds of birds fly openly day by day, but 



PRINCIPAL ROUTES OF MIGRATIONS, 

 SHOWING EXTENT OF FLIGHT 



many of the ordinary night-fliers and the more 

 timid species migrate only by night, sheltering 

 themselves in secluded places during the day. 



There is a difference observable in the spring 

 and fall flights. In the former, the birds are 

 fresh and strong from their long winter's feed- 



