The Birds and Poets 53 



were disadvantageous to them, and sought condi- 

 tions that were more favorable. In the same 

 manner they formed habits of wandering in search 

 of food. In their wanderings, which gradually 

 have been extended over wider and wider areas, 

 they have discovered attractive feeding grounds 

 and suitable nesting places; and when to this are 

 added the other recognized influences, the cause of 

 or reason for migration is about as fully explained 

 as it ever will be. 



When about to give birth to a calf, the domes- 

 ticated cow will sometimes break out of the barn 

 or yard and hide herself in the protecting woods 

 or brush. Although a pet cow, she will defend 

 the retreat against all comers, and allow no one 

 to approach her young. This action represents 

 a reversion to the habits of her wild ancestors, 

 forced to the surface by the great elemental fact 

 of reproduction. Many wild animals act in a 

 similar manner under these circumstances, often 

 travelling considerable distances. I have some- 

 times wondered if it might not have been a simi- 

 lar elemental impulse in the birds which in the 

 dim past was the real cause or origin of the present 

 fixed habit of long-distance migration. The ease 

 with which the birds might respond to this impulse, 

 with their wonderful powers of flight, would make 

 such movements on their part most natural. 



Certain it is that as our northern spring 

 approaches, the sex impulse, the strongest of all 

 animal impulses, upon which reproduction and 



