B 



IV 



THE BIRDS' AIR LINE 

 EFORE we knew as much about the earth 



as we do now, the complete disappearance 

 of many birds in the fall and winter was con- 

 sidered a great mystery. With us one day, they 

 were gone the next. Then, months later, they 

 suddenly reappeared. Where had they been? 



At one time it was thought that some birds 

 flew to the moon. Others, particularly the Swal- 

 lows and Swifts, were believed to fly into the 

 mud and pass the winter hibernating like frogs ; 

 while the European Cuckoo was said, in the fall, 

 to turn into a Hawk. 



Why birds were ever thought to winter in 

 the moon it is difficult to say; but that Swallows 

 were considered to take refuge in the mud at this 

 season is not so surprising. We have seen how 

 these birds sleep in the reeds in the marshes. 



