MIGRATION i6s 



across the sea, but this is not the way with the majority. 

 Data have been arrived at in various ways, (i) By means 

 of captive balloons Lucanus determined the height at 

 which stuffed specimens of well-known birds became 

 invisible. Thus a rook was a visible spot at 750-800 metres, 

 but invisible at 1000. A buzzard was just visible at 1000 

 metres, which showed that Gatke's estimate of observing 

 one at 3300 metres was quite out of the question. 



(2) Ornithological astronomers have sometimes identified 

 migrants crossing the telescope's field and have estimated 

 the height at which they were flying. Spill's estimates 

 (quoted by Hilzheimer) gave 2000-3000 metres for many 

 birds, but there is almost certainly some fallacy here. 



(3) In direct aeronautical observations Lucanus saw no 

 migrants above a height of 1000 metres, which is, he says, 

 the height that yields the optimum breadth of view. 



In his recently published book on migration, Lucanus 

 (1921) shows that there has been much exaggeration of the 

 altitude of migratory flight. Apart from birds of prey, the 

 maximum height scientifically observed has been 2200 

 metres — a unique case of small swallow-like birds ; there 

 are only a few records over looo metres ; there are compara- 

 tively few between 400 and 1000. The great majority of 

 migrants journey at an altitude below 400 metres. 



High-flying birds like geese, cranes, and storks cannot be 

 credited with an altitude of more than 1000 metres, though 

 there is one case of what was probably a flock of cranes at 

 1400 metres. Of records above 400 metres there may be 

 mentioned — a swallow at 450, a flock of cranes at 500, two 

 storks and a buzzard at 900, and a lark at 1900 metres. An 

 eagle tops the list at 3000 metres, but this was not in migratory 

 flight. 



(c) Velocity of Flight. — It is difficult to obtain secure 

 data as to the rate of migratory flight, and many exaggerated 

 statements are current. A carrier-pigeon has been known 

 to fly at the rate of 55 miles an hour for four hours on end, 

 and Gatke said that curlews, godwits, and plovers flew to 

 oyster-beds four miles off in one minute. On very 



