932 Col. K. Meinertzliagfn on the Altitude [I^J'^j 



£oo', mist, etc. {vf. also Aquila, x. p. 71), and this Las Ijeen 

 aiiij)lv }»roved by recent observations. No student of 

 migration can have failed to observe that in the heioht of a 

 migratory passage, passage-migrants are not so much in 

 evidence in clear and still, as in dull or rainy weather. The 

 reason is obvious. Birds, as do our air pilots, like to see the 

 earth, and descend in bad weather to a position where they 

 can see it, or if the weather becon.ies too bad, flight is stopped 

 altogether. I do not believe that weather has any other 

 effect on the altitude of mioration than this. 



I frankly do not understand Gaetke's above-quoted state- 

 ment, for a south-easterly wind in Heligoland would be a, 

 dry wind entailing clear weather, and with such weather 

 conditions migratory flight is normal, the altitude of 

 migratory flight not being brought nearer to the surface 

 of the earth. 



(1)) TJie use of shjlit Inj migratory birds. 



It is generally accepted that of all animal life, specializa- 

 tion of sight reaches its highest degree of development among 

 birds. Lewis (Emu, xv. p. 217) considers birds to have an 

 acuity of vision 100 times greater than that of huuian beings. 

 The wonderful eyesight of Vultures, the vision which permits 

 Cormorants to fish in muddy waters or a Kestrel to pick up 

 small beetles when hovering at 200 feet or more, cannot fail' 

 to impress us. And I was recently still more impressed 

 when sitting on the snows of Ida's summit in Crete, Out of 

 the clouds rushed hundreds of Alpine Swifts which at once 

 commenced feeding within a few feet of me. Their twists 

 and turns denoted an abundance of food, and althouoh some 

 birds took insects within a few feet of me, I could detect no 

 sign of insect life. On shooting one, I found the birds were 

 catching a minute beetle scarcely so large as a pin's head. 

 To do this when travelling at some 80 miles an hour, does 

 indeed bear out Lewis's comparison of the acuity of vision 

 as between men and birds. 



I now wish to quote Dixon (' Migration of Birds') : — 



"In no part of the world do any regular migration 



