228 Col. K. Meiuertzhageii on the [Ibis, 



XII. — ^onie. preUmhiary remarks on the Velocity of Migratory 

 Flight among Birds, tvith special reference to the Pala- 

 arctic Region. By Colonel R. ]\Ieinertzhagen, D.S.O., 

 M.B.O.U., F.Z.S.' 



Thk question arises at once as to whether migratory flight 

 is of a different nature to daily Higlit in search of food or to 

 escape enemies. We have some interesting opinions on this 

 subject. Gatke 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 attained 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 

 migrating 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 ver}^ slow\ He goes on to say that during day- 

 migration the smaller land-birds seldom fly faster than 

 20 miles per hour^ though larger birds move somewhat 

 more rapidly. 



I believe Gatke's theory to be based on faulty evidence, 

 as 1 hope to show later. Moreover, birds would experience 

 greater difticulties in flying in the " more elevated layers of 

 the atmosphere,'' as the atmosphere is rarer and therefore 

 oft'ers a less suitable mixture on which their wings can beat. 

 They would experience the same difficulties as a man trying 

 to swim in froth. 



jNIy own observations fend to show that migratory flight 

 differs very little in its velocity from the flight of daily move- 

 ment, and I see no reason why it should or how it can be so. 

 I believe ujigratory flight to be steady and unhurried, and 



