1920.] of the Mi(jratunj Flif/ht uf Birds. 935 



up landmarks at over say 50 miles, unless such landmarks 

 be the dividino- line between the sea and land, oi- perhaps 

 some snow-clad range. (The snows of Mount Kenya ar(! 

 visible by moonlight at over ()0 miles distance.) 



But I have seen Quail and Hoopoe at sea on aiUunm 

 passage in the earliest hours of dawn, when land could not 

 have been visible to them from their position almost touching 

 the surface of the waters. I see no reason to suppose Quail 

 and Hoopoe trai^el higher by night than by day, and if they 

 do not require the assistance of landmarks by day. why 

 should they require such aid by night ? 



In this connection, Cooke "^j in a very masterful essay, 

 gives a curiously confused statement on this rather con- 

 fusing subject. He says : — 



" Sight undoubtedly does phiy a part in guiding the 



night journeys also. On clear nights, especially when 



the moon shines brightly, migrating birds fly high and 



the ear can scarcely distinguish their faint twitterings; 



if clouds overspread the heavens the flocks pass nearer 



the earth and their notes are much more audible ; and 



on very daik nights the flutter of vibrant wings may be 



heard but a few feet overhead." 



How can sight play a part in guiding biids on night 



journeys when on dark nights birds fly but a few feet above 



the surface of the earth ? 



As regards an oft-voiced view that greater altitude makes 

 flight easier for a bird, I can onl}^ quote the experience of 

 our ]loyal Air Force, that as altitude increases, the machine 

 has greater difficulty in maintaining its height and speed. 



Conclusions. 

 A great deal more evidence of an accurate nature must be 

 obtained before any definite facts can be ascertained, ;ind the 

 following conclusions must only be regarded as provisional. 

 1. Birds need not, for the purposes of migration, ascend 

 much beyond 5000 feet above the level of the earth, 

 nor indeed do they. 



* Bird Migratiou, U.S. Dept. Ayricult. Bull. uo. 185, I'Jlo, p. 27. 



