FACTS ABOUT BIRDS. 



201 



chiefly seed-eaters, whose food is not 



covered by snow or frost. 



Many birds have air-tubes connect- 

 ing their lungs with their hollow 



bones ; so that, in flying, the air passes 



into all parts of the body and makes 



it lighter. The real mystery of flight 



is in the birds' wings. Could any 



thing be at once so light and so strong 



as the quill, which is the lower, naked 



part of the feather? 



Then look at the vane, or web, 



which is fastened to the after-shaft 



the upper part of the feather. Each 



layer of the vane is called a barb, and 



cleaves closely to its fellow by hooks, Fi *' 13 ' Feather - 



or barbules, as is seen in the magnified barbs (Fig. 



13), on either side of the quill. This arrangement 



makes the feather a 

 wonderfully strong and 

 light oar to row the 

 bird-ship. 



Young birds, like 

 : ; young children, must 

 ;J learn their songs. The 

 i singing muscles of the 

 child are in the upper 

 part of the windpipe, 

 and can only be suc- 

 cessfully used by prac- 

 tice. The singing mus- 

 cles of the bird are in the lower part of the wind- 



House "Wren. 



