BIRDS OF NEW YORK 



71 



country, migrate largely by day, and are often seen as they pursue their 

 way at a moderate elevation. Even the thrushes and warblers are occasion- 

 ally found to migrate by day, passing from one grove or orchard to the 

 next in their route. At such times they fly near to the ground, but when 

 they migrate by night they fly high above the tree tops, usually at an 

 altitude of several hundred feet, and sometimes thousands of feet above 

 the earth. 



The instinct to move about in search of a favorable food supply is 

 common to all species of birds, even the most sedentarv, like the Canada 

 grouse and Banded-backed woodpecker, which wander about within the 

 limits of the spruce forest to a considerable extent. Others, like the Black- 

 backed woodpecker, \-enture still farther and have been taken in all parts of 

 the vState. In some species, like the common Crow and the Robin, there is 

 merely a withdrawal from the northern portion of their breeding grounds 

 while as species they are resident in the wamier portions of their range. 

 Thus it would be possible to mention all degrees of the migrator^• habit up 

 to the most extreme, represented by such birds as the Whistling plover which 

 breeds on the islands and shores of the Arctic ocean and passes the winter 

 as far south as the valley of the Parana and the plains of Patagonia, merelv 

 visiting us for a few days on its semiannual journev of 8000 miles. 



There can be no doubt that the failure <)f the food supph- and the 

 desire to live in an even teniperature are factors which enter into the solu- 

 tion of the problem of bird migration. Winter drives the birds south and 

 like so many chickens which have been chased from a forbidden garden they 

 come flocking back again as soon as winter has withdrawn. For in the wide 

 northern lands which springtime opens tip, with their wealth of food and 

 shelter and safe retreat for rearing their young, the birds have ample reason 

 to return to the spot of their nativity. Undoubtedly the glacial period had 

 much to do with accentuating the yearly effect of the seasons and stamping 

 in the racial instinct of migration, so that at the present day it is an impulse 

 which must be obeyed, in maiiy instances, even before the food supply 

 fails; for those which wait tof) late may be destroyed before the winter 



