HOW THE BIRDS KNOW 



while ours of the 

 same species have 

 gone farther south. 

 This marvellous 

 knowledge, which 

 guides them and en- 

 ables them to perform 

 miracles, almost 

 passes the compre- 

 hension of man. 

 Birds of many species 



321 



have such unerring 



Making up her mind to start 



A humminghird that did 

 not know when to migrate 



knowledge of the 

 workings of nature 

 that they migrate 

 when it is necessary 

 and remain where 

 they are when it is 

 not. For example: 

 during the bitter win- 

 ter of 1917-18 when 

 extreme cold began 

 in November and 

 lasted in such pro- 

 longed form that we 

 experienced killing 

 frosts in June, 

 there was not a robin 



