THE WOODPECKER'S TOOLS : HIS FOOT 81 



they were not good nippers unless they were 

 nearly equal-limbed. Next we studied the wood- 

 pecker's foot to learn about that extra hind toe. 

 Then it occurred to us that four toes were not 

 necessary, since some of our best climbers have 

 but three. What was the essential point? 

 Might it not be a foot equally divided without 

 reference to the number of toes? But that is 

 the principle of a pair of nippers. Then came 

 the question, Is there any similarity in their use ? 

 Yes, the nippers are used to lift heavy weights, 

 and the woodpecker's foot is used to lift his 

 heavy body in just the same way, hy taking 

 hold of a flat, smooth surface. We conclude 

 that a wide-spread, equally divided, nipping foot 

 would be the best device possible for the wood- 

 pecker's way of living, and we find by examina- 

 tion that every woodpecker shows this type of 

 foot. 



There is additional evidence that this is the 

 right explanation. Our only other North Ameri- 

 can birds that climb on the bark of trees profes- 

 sionally, as we may say, are the brown creepers 

 and the nuthatches. In both these the tarsus is 

 short, as we found it in the woodpeckers, and 

 the hind toe and its claw are fully equal to the 

 middle toe and claw, making an equally divided 

 foot. On the other hand, the foot with two toes 



