SOME PRELIMINARY REMARKS ON THE VELOCITY OF 

 MIGRATORY FLIGHT AMONG BIRDS, WITH SPECIAL 

 REFERENCE TO THE PALiEARCTIC REGION. 1 



By Col. R. Meinektzhagen, D. S. O., M. B. O. U., F. Z. S. 



The question arises at once as to whether migratory flight is of a 

 different nature from daily flight in search of food or to escape ene- 

 mies. We have some interesting opinions on this subject. Giitke tells 

 us that the speed of birds during their daily locomotions in the air has 

 not an approximate relation to the wonderful velocity of flight at- 

 tained by them during their migrations. He accounts for such 

 enormous speed by the fact that birds migrate in the more elevated 

 layers of the atmosphere, in which more uniform conditions prevail, 

 and which are less subject to powerful meteorological disturbances. 



Cooke ("Bird Migration ") , on the other hand, thinks that migrat- 

 ing birds do not fly at their fastest. He believes that their migrating 

 speed is usually from 30 to 40 miles an hour, and rarely exceeds 50. 

 Flights of a few hours at night, alternating with rests of one or more 

 days, make the spring advance very slow. He goes on to say that dur- 

 ing day migration the smaller land birds seldom fly faster than 20 

 miles per hour, though larger birds move somewhat more rapidly. 



I believe Giitke's theory to be based on faulty evidence, as I hope to 

 show later. Moreover, birds would experience greater difficulties in 

 flying in the " more elevated layers of the atmosphere," as the atmos- 

 phere is rarer and therefore offers a less suitable mixture on which 

 their wings can beat. They would experience the same difficulties as 

 a man trying to swim in froth. 



My own observations tend to show that migratory flight differs 

 very little in its velocity from the flight of daily movement, and I see 

 no reason why it should or how it can be so. I believe migratory 

 flight to be steady and unhurried, and that birds only fly at their 

 fastest when pursuing or when pursued. Any one who has watched 

 a falcon being flown at a rook will be struck by the speed which the 



1 Reprinted by permission from The Ibis, April, 1921, pp. 228-238. 



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