930 Col. R. Meinertzliagen on the Altitude [Ibis, 



certain day, but how seldom one sees tliose hosts in movement 

 by day or hears them passino- l)y night. 



I recently made some enquiries about the numlier of diick 

 and quail which are animally slaughtered for the market in 

 Egypt. Near Port Said alone over 000,000 Duck are 

 killed yearly, and over three million Quail are exported 

 annually from Egy|)t, and these colo«sal figures only 

 represent a part of the total butcher's bill. Who sees these 

 millions arrive or depart ? Who ever hears or sees them 

 moving. I have but one record — a wonderful experience — 

 by an eye-witness, and that was of Duck passing north en 

 masse near Port Said in the spring of 1920. From the 

 description it was a sight that few are privileged to see. 



So in this respect we must accept Gaetke's theory that 

 invisible migration is the normal, but I cannot agree ihat 

 migration takes place at such elevations as .20,000 feet. And 

 the reason that normal migration is generally invisible can 

 only be that most birds travel by night. This is confirmed 

 by the fact that so little migratory movement has been 

 observed from aeroplanes, when we realize that in north- 

 eastern France, Palestine, Mesopotamia, and East Africa the 

 air has been so thoroughl}^ watched throughout several 

 migratory seasons. 



It is indeed tempting to assert that migratory movement 

 proceeds above the possibility of normal observation from 

 aeroplanes — say at 20,000 feet or over. But our evidence 

 does not allow of this. In f'acl, the nearer we get to 

 20,000 feet, the scantier becomes our evidence. Omitting 

 for the moment the American telescopic observations bv 

 moonlight, let us take all instances of birds observed in 

 flight at 5000 feet or over, and we have : — 

 15 cases of Lapwing, 



4 ,, ,j Greese, 



;-) „ „ Crane, 



2 ,, „ Rooks, 



2 „ „ Waders, 

 10 ,, ,, other birds ; or 36 cases in all. 



Now of tiiese the Birmingham Kestrel^ the Mosul S 



