THE UNCHARTED SKY 151 



"Can any one count the number of birds that 

 pass over our heads every spring and fall I They 

 are as the sands of the sea for multitude. Un- 

 counted billions of birds pass twice a year over 

 any given spot in the Southern States which is 

 on or near the main migration routes." 



'^Why don't we see more of them?" asked the 

 boy. 'T've never noticed such big flocks of 

 migrants as you talk of!" 



''One of the chief reasons is that they fly too 

 high," was the expert's answer. ''Astronomers, 

 observing the sun by telescope by day, or the moon 

 by night, have seen birds pass in a steady stream 

 across the face of the sun or moon, flying rapidly 

 at an immense distance overhead, possibly three 

 miles high. Not one of these birds could be seen 

 with the naked eye. This rush of the feathered 

 tide, spreading sometimes for many square miles 

 over the heavens, goes uncounted and unseen." 



"Why should they fly so high?" asked Shan. 



** Freedom from enemies, for one thing," was 

 the reply, "but even more important, there is far 

 less resistance in the air and a bird can fly faster 

 with less effort. It is because they fly so high 

 that their voices are not heard in clear weather, 

 while on a dark or cloudy night they fly nearer to 



