THE WOODPECKER'S TOOLS: HIS BILL 75 



ravens and many kinds of finches, among other 

 birds, none of which dig in the bark of trees or 

 raise a dust, have their nostrils as completely 

 covered, we see that we have perhaps discovered 

 a use for these nasal tufts but not the cause of 

 their being there. We must be careful not to 

 mistake cause and accompaniment in our endeavor 

 to explain differences in structure. 



Let us see what we have learned and how to 

 interpret it : 



That the woodpecker's bill is a combination of 

 drill and pick-axe. 



That the shape varies with the use to which it 

 is most commonly put. 



That the use varies with the food principally 

 eaten ; or, what is a step farther back, that the 

 different kinds of food must be sought in differ- 

 ent places and by different methods, and there- 

 fore require different tools. 



Therefore the shape of the woodpecker's bill 

 has a direct relation to the kind of food he eats. 

 Please notice that we do not assert that it causes 

 him to eat a certain kind of food nor that a cer- 

 tain diet may not have affected the shape of the 

 bill, causing it to be what we now see. Both 

 may be at least partially true, but to prove 

 either or both would need profound study, and 

 all that we have observed is that the shape of- 



