934 Col, 11. Meincrtzliaoeii on the A/tit ude [Ibis, 



instances have come within my personal knowledge. I have 

 seen : — 



miles 



1. Mount Ida in Crete from a ship at 110 



2. The Peak of Teneriffe from a ship at 120 



3. The Island of Rodriguez from Mauritius on clear days and 



from 1500 feet in the latter island. Distance 125 



4. Kilimanjaro Mountain from Nairobi^ visible on any clear day. 140 



5. The snows of the Himalayas from INIeerut on a December 



evening 150 



6. Mount Kenya (17,000 feet) from the Mau Plateau (8000 feet) 



on a clear dawn 160 



7. From an aeroplane at 7000 feet over Hebron on a clear still 



evening in April 1917, I clearly saw the Dead Sea, the 

 Mediterranean, Mount Ilermon, the Gulf of Akaba, and 

 Mount Sinai 200 



Add to this a bird's acuity of vision and the clear atmo- 

 sphere which is attained at a little distance from the earth, 

 and I can see no reason why a migrant in most parts of 

 Europe or Asia shouhl require a greater elevation than 

 5000 feet or so to pick up landmarks — if altitude is required 

 for picking up landmarks, 



I do not believe that birds crossing the wider reaches of 

 the Mediterranean pick up Africa before they lose sight of 

 Europe. If the lower-flying Passeres, Quail, Hoopoe, etc. 

 can do without landmarks as a guide, why should not other 

 birds? 



And if altitude is not re<inir(nl for picking np hmdmarks, 

 surely 5000 feet is sufficient for safety, lor local orientation, 

 locating feeding or resting grounds. Lucanus^s assertion 

 that perspective disappears at about '.VMH) feet nuiy be true 

 for northern Germany, but does not hold for mountainous 

 country, where perspective is still good up to at least 7500 

 feet, especially with a slanting sun. 



I must ask my readers to accept, for the purposes of this 

 paper, my view that birds do not rely to any large extent on 

 landmarks to guide them on migration. It is a question 

 outside the scope of this ])aj)er, but which I hope to deal 

 Avitli at a near. date. I need, therefore, only mention that at 

 uight no degree of acuity of vision w^ill assist a bird to pick 



