BIRD STUDY 39 



occasional migrations. A noted instance of this kind occurred 

 in 1904, when heavy snows in the northern regions brought the 

 Lapland Longspurs to South Dakota on the wings of a storm 

 in great numbers. The writer of this chapter was returning 

 home about 10 o'clock at night. A keen north wind was blow- 

 ing, and the air was filled with snow as fine as sifted flour. It 

 was the beginning of a vicious storm. Several times he stopped 

 to listen. The storm seemed filled with birds moving south- 

 ward. Their sweet calls were heard in every direction. The 

 next morning Vermillion was filled with dead and, wounded 

 birds. Becoming bewildered in the storm, they had been hurled 

 against buildings, telephone poles and wires. Such migrations 

 are not uncommon and seem to be occasioned by lack of food, 

 or by the covering of food by snow in the birds' usual winter 

 habitat. 



The great majority of birds migrate at night; noted ex- 

 ceptions are the birds of prey, such as Hawks and Vultures, and 

 birds that gather their food on the wing, such as Swallows and 

 Swifts. Other birds, such as Ducks and Geese, seem to migrate 

 partly by day and partly by night. 



It has generally been thought that birds migrate at night 

 to avoid attack by their enemies. It seems reasonable, however, 

 to suppose that the food problem is a larger element than the 

 safety problem. Swallows and Swifts must migrate by day to 

 supply themselves with food. Hawks and Vultures have better 

 opportunity for securing food in the course of the day's migra- 

 tion than they would have by migrating at night and resting 

 in some particular place during the day. The food of the great 

 host of small birds is such that they must spend practically the 

 whole day seeking it. If they migrated by day they would not 

 be able to secure sufficient food, for they cannot search for it by 

 night. Ducks and Geese, of course, need only to descend into 

 any corn or wheat field for a few hours, morning and evening, in 

 the course of flight. This is their regular method of feeding 

 when they remain in one locality. 



Bird flights are preferably upon still, clear nights, and 

 are thought to reach at times an altitude of at least three miles. If 

 a storm is raging, the birds cannot hear one another's calls and, 



