THE NIGHT FLYERS 



pressure grows less. So it is much easier for a 

 bird to travel at a height of two or three miles 

 than near the ground. Beyond a certain height 

 the air would become so thin that the bird could 

 not live. Just how high this is we do not know ; 

 with man it is about five miles. 



The tops of the highest mountain peaks in the 

 Andes are nearly that height, but the great Con- 

 dor soars easily far above them. On some of 

 these same mountains small Flycatchers and 

 Humming-birds live the year round nearly three 

 miles above the level of the sea. Thus we know 

 that at even this height the night flyers could 

 travel comfortably. 



MORE LIGHT ON THE NIGHT FLYERS 



Few bird students have had a better oppor- 

 tunity to see birds on their night flights than was 

 afforded Dr. Witmer Stone in Philadelphia. On 

 the night of March 27, 1906, a great lumberyard 

 in that city caught fire, and like a vast search- 

 light it showed the bird armies flying overhead. 

 For at least several hours the feathered invaders 



7 8 5 



