XII
THE WOODPECKER’S TOOLS: HIS FOOT
We have studied the woodpecker’s bill and have found that it is a very serviceable tool. We shall find that his feet are equally well adapted to their work.
Here is the foot of a woodpecker. Observe how it differs from a chicken’s foot, or a sparrow’s foot. What is it that especially fits it for climbing? Perhaps you will notice that the tarsus is short, and you may be able to explain why it would be a disadvantage for a climbing bird to have long legs, as well as why it is a help for him to have long toes. Toes long and legs short is the rule with the woodpeckers.
Foot of Woodpecker.
I never see a woodpecker’s foot without thinking of an iceman’s nippers with their short handles and long, sharp-toothed jaws. They are designed for similar uses,—to lift heavy weights by laying hold of smooth, flat surfaces. The iceman sets his nippers into the ice and lifts the block; but the bird sets his claws into the tree and lifts his own body.
Suppose the nippers had one short jaw and one long one, would they then take as firm hold as they do with jaws of equal length? In perching birds the hind toe is much the shortest, but they sit balanced upon a limb and have merely to hold themselves in position. The woodpecker climbing a tree-trunk is out of balance; he would fall off unless he had a firm grip; and he could not get this firm hold if his hind toes were not long enough to give his foot a nearly equal spread back and forward. Other birds grasp a limb with the whole under surface of their toes, but the woodpecker when on a smooth, upright tree-trunk nips it only with his toenails. Try with your own hand to hold a stick as large and heavy as you can grasp, and you will see that when you clasp your hand around it as a perching bird takes hold of a perch, it makes little difference that the thumb is shorter than the fingers, but when you try to nip it with your finger tips alone, you must bend your fingers until they are not much longer than your thumb,—that is, a pair of nippers must be equal jawed.
This simple illustration shows why the woodpecker’s foot reaches as far backward as forward. But a sensible objection may be raised, namely, that as there are two hind toes of unequal length, it is by no means certain which is the more necessary.