48 THE MIGRATIONS OF BIRDS 



findings^ in brief, are that it is exceptional in flying 

 to meet with birds above an altitude of 5,000 feet, 

 and that the bulk of migration is performed below a 

 height of 3,000 feet from the earth. Though most of 

 the observations that he cites were made during the 

 day, he holds with reason that there is no evident 

 cause for considering that nocturnal migrants pass 

 at a higher plane than those observed by day. Since 

 the observations that he cites were made by pilots 

 who, during several years of war, had the air across 

 broad areas in the Palaearctic region under constant 

 close surveillance, we must accept them as conclu- 

 sive. In several hundred records by airplane it ap- 

 pears that there were only 32 observations of birds 

 above 5,000 feet, and only seven above 8,000 feet. 

 Meinertzhagen considers that ordinarily birds prefer 

 to descend below cloud level, though this is not uni- 

 versally true. On nights of fog or rain birds pass 

 very near the earth, and it is then that we may ob- 

 tain some idea of the vast hordes of migrants that 

 fill the air, as their notes and calls come drifting 

 down from the sky. 



Day migrants among shore-birds may pass at con- 

 siderable altitudes, as it is common experience in 

 shooting, particularly in arid regions where suitable 

 feeding grounds are widely separated, to have 

 yellowlegs or black-bellied plover come swiftly 

 down to the decoys from heights at which the eye 



