362 THE STRUCTURE AND LIFE OF BIRDS chap. 



the altitude at which the bird was flying. Eleven 

 birds were seen shortly before eleven o'clock and 

 for these the lower limit was 3,000 feet above the 

 earth's surface, and the higher 15,100 — i.e. only just 

 short of three miles. If they were one mile distant, 

 they were flying at the lower altitude mentioned, if 

 five miles, at the higher. It is probable that some of 

 them were near the higher limit, since they passed 

 far more slowly across the field of the telescope than 

 others. So clear a view was obtained that Mr. 

 Chapman confidently affirms that he recognised a 

 Carolina Rail and a Snipe by their flight. 1 



Herr Gatke strenuously maintains that birds fly to 

 enormous heights. He quotes Humboldt who, when 

 himself 15,578 feet above the sea level, saw a Condor 

 so high overhead that it looked like a small speck. 

 Migratory birds often pass at so great a height that 

 they altogether escape notice. When a Crane with 

 a wing expanse of seven to eight feet rises so high 

 that a good eye can hardly see it, the elevation attained 

 must be, he calculates, not less than 15,000 to 20,000 

 feet, and though such unassisted observations cannot 

 claim to be exact, yet they help us to the rough 

 conclusion that the altitudes reached are very great. 

 Nearly all migrants are high flyers, coming down 

 only when compelled by the weather. Crows, Star- 

 lings, and Larks are exceptions and habitually fly low, 

 only a few hundred feet above the sea. 



It is usually on dark misty nights that the cries of 

 migratory birds are heard. It is then that they 



1 See The Auk, 1888, p. 38; the Nuttall Ornithological 

 Bulletin, vi., p. 97 ; and Newton's Dictionary of Birds, p. 563. 



