1920.] of the Migratory Pl'ujU of Birds, 931 



the Salisbury Rooks, and the Lainmergeier were undonbtodly 

 not niigratin<i; and need not bo considered. Ot" the remainder, 

 the higliest seven recorded altitudes are 15,000, 12,000, 

 10,500, 10,000 (twice), 9,500, and 8,500 feet. Below 8000 

 feet observations become more frequent, whilst between 

 3000 and 5000 feet they are not uncommon. Now aerial 

 observation in France and Palestine extended well above 

 8500 feet, and if mass migration did occur above that 

 elevation, it could not fail to have been observed even on its 

 outskirts. The very lack of evidence, where evidence should 

 exist, convinces me that flight at over 5000 feet is abnormal 

 whether by day or night. 



Regarding the American telescopic observations across the 

 face of the moon, I prefer to believe that Chapman recognized 

 a Carolina Rail by moonlight at under half a mile than at 

 about two miles distance. Though I do not for one moment 

 wish to belittle these most interest! ii"' and instructive 

 experiments, I feel tlmt observations with such gigantic 

 margins of estimation should be accepted with care until we 

 iyei a laroe series to work on. 



Before attempting to reach a final conclusion on this 

 subject, it is necessary to take up the questions of (a) The 

 effect of weather on the altitude of migratory flight ; and 

 . (I)) The use of sight by migratory birds. 



(a) The effect of weather on the altitude of miyratonj 

 flight. 



Gaetke states that during both spring and autumn 

 migrations without exception, all species approach in largest 

 numbers to the earth's surface when very light south- 

 easterly winds, acconq)anied by clear warm weather, happens 

 to prevail for any length of time in the lower reaches of the 

 atmosphere. 



Sufficient has been written by students of migration to 

 show that neither velocit}^ nor the direction of the wind lias 

 much effect on the altitude of migratory flight. Herman, 

 however (Aquila, i. p. 9), shows clearly that migratory 

 flight is brought nearer the earth in bad weather — storms, 



