362 THE STRUCTURE AND LIFE OF BIRDS cHapP. 
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—z.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+ 
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 
"See The Auk, 1888, p. 38; the Nuttall Ornthological 
Bulletin, vi, p. 97 ; and Newton’s Dictionary of Birds, p. 563. 
