The Woodpeckers

by Fannie Hardy Eckstorm

Head of Ivory-billed Woodpecker.

Any one who has lived in a granite country knows the deep round holes that stone masons make when they split rock. Did you ever wonder why they are as large at the bottom as at the top? If you remember the shape of a mason’s drill, you will recollect that it looks a little like a stick of home-made molasses candy bitten off when it was just soft enough to stretch a little. The mason’s drill is a round iron rod with a thin, flat end, sharpened on the edge and a little pointed in the centre. In the flattening of the sides and the width across the tip its end resembles that of a typical woodpecker’s bill. The woodpeckers that drill for grubs, especially the largest, the logcock and the ivory-billed woodpecker, have the tip remarkably flattened. The likeness to the drill does not go farther because the woodpecker’s bill is a combination tool; but it is drill-pointed rather than pick-pointed.

What is the advantage of this compressed tip? Can the bird pick as well as he could with a sharp point? The bird and the mason reap the same benefit from this form of tool. A sharp-pointed drill would bind in the hole and could neither be driven ahead nor removed without difficulty, but the sharp-edged tool cuts a hole as wide as the instrument. There is, of course, some difference between working in stone and in wood, but the principle is the same. The mason strikes his drill with his hammer and cuts a crease in the stone; then lifts and turns the drill, cutting a crease in another direction; and so by continually changing the direction of the cuts until they radiate from a centre like the spokes of a wheel, he finally reduces a little circle of stone to a powder fine enough to be blown out of the hole. In drilling for a grub the woodpecker must do much the same thing. He wishes to keep his hole small at the top so as to save work, yet it must be large enough at the bottom to admit the borer when nipped between his mandibles; therefore he needs an instrument that, like a drill or a chisel, will cut a straight-sided hole. Indeed, we might call it a chisel just as well if it were not a double-wedge instead of a single wedge and if it did not move when it is struck instead of being held stationary beneath the blows.

When he is digging his house the woodpecker uses his bill as a pick-axe. When he is digging for grubs he uses it as a drill. Now some species drill very little and some a great deal, according to the number of grubs they feed on; but all dig holes to nest in,—that is, all use their bills as picks but only a few employ them as drills. The flickers, for example, seldom drill for grubs, their food being picked up on the surface or dug from the earth; yet they excavate the deepest, roomiest holes made by any woodpeckers of their size; they use their bills effectively as pick-axes, but seldom, very seldom, as drills. And what do we find? No drill-point—not a truncate, compressed bill fit for drilling, but a sharper, pointed, rounded, curving bill. Notice the ordinary pick-axe and see how much nearer the flicker’s bill than the logcock’s or the ivory-billed woodpecker’s it is. Why is a flicker’s bill better for being curved also? Why do the drilling woodpeckers have a perfectly straight bill? We should find by studying the birds and their food that there is a direct relation between the shape of the bill and the amount of drilling a woodpecker does; that the grub-eating or drilling woodpeckers have a straight bill, for working in small deep holes, while the flickers have a curved bill for prying out chips. And we should note that the flicker’s bill is most like the ordinary bill of perching birds, while the drilling bill, as typified by the logcock’s and the hairy woodpecker’s bills, is a more specialized tool, limited to fewer uses, but more effective within its limits.

There is another detail of the woodpecker’s bills which casts light upon their habits. The species that drill most have their nostrils closely covered by little tufts of stiff feathers, scarcely more than bristles, which turn forward over the nostril. The density and the length of these tufts agree very well with the kind of work the woodpecker does; for in the hairy and the downy, which are continually drilling and raising a dust in rotten wood, they are very thick and noticeable, while in the red-head and the sapsucker they show as scarcely more than a few loose bristles, and in the flicker they barely cover the nostril. This seems a plain provision to keep the dust out of the bird’s lungs; and we might cite as additional evidence the fact that the only other birds of similar tree-pecking habits, the nuthatches and the chickadees, have their nostrils protected in the same way. But we must always be cautious before drawing inferences of this sort to see what may be said on the other side. When we recollect that the crows and 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 different places and by different methods, and therefore 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 certain 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 the woodpecker’s bill is adapted to his food and that it varies with the kind of food he eats, or, to be more exact, with his ways of procuring it.