third of his food, their larvae do not form any part of it. Half his food
for the entire year is vegetable, and the animal portion is composed
principally of beetles, ants, caterpillars, and grasshoppers, which in
winter time are hidden in snug places, or are dead under the snow. There
are few berries in winter. The few seedy, weedy plants that stick up
above the snow give to the birds the little they have; but the
red-head's vegetable fare is limited at that season and his animal food
almost lacking. Winter in the North is all very well for the hairy and
downy cousins that like to hammer frozen tree-trunks for frozen grubs;
but our red-headed friend does not eat grubs by preference. Rather than
change his habits he will change his boarding-place. So he is a
migratory woodpecker, though the woodpeckers are naturally home-loving
birds, and do not migrate from preference. If, however, he can lay up a
store of vegetable or animal food, he can winter in any climate.
Hoarding is thus an invention as important to the woodpecker world as
electric cars and telephones are to men. The probabilities are that
this is a recent improvement in the red-head's ways of living.
Another set of facts increases the probabilities of our supposition. It
is a very delicate subject to handle because it affects the reputation
of a family in good standing; but there is positive proof that sometimes
the red-head has been guilty of crimes which would give a man a full
column in the newspapers with staring headlines. If such deeds were not
a thousand times less common among woodpeckers than they are among men
the red-head would be declared an outlaw. He has been proved to be a
hen-roost robber, a murderer, and a cannibal. In Florida he has sucked
hen's eggs. In Iowa he has been seen to kill a duckling. There is a
record in Ohio that he pecked holes in the walls of the eaves swallow's
nest and stole all the eggs, and that he was finally killed in the act
of robbing a setting hen's nest. Within the space of fifteen years, from
Montana, Georgia, Colorado, New York, and Ontario, in addition to the
records mentioned already from Florida, Ohio, and Iowa, come accounts of
his stealing birds' eggs and murdering and eating other birds. The
evidence is indisputable.
It is charity to suppose that this is the work of natural criminals, or
of degenerate, under-witted, or demented woodpeckers. Why should there
not be such individuals among birds? One point is certain: so notable a
habit could not long escape detection, since it is a barnyard crime. He
who robs hen's nests gets caught--if he is a bird. Either these
occurrences are very rare, not seen because of their extreme rarity, or
they indicate a new custom just coming in. And the same is true of the
habit of hoarding food; it is rare, or it is new.
The frequency of such occurrences can be determined only by observation;
but the time of their origin might be approximated in another way. If we
could fix the date when the bird could not have done what he is now
doing for simple lack of opportunity, we might say that the habit has
been acquired since a certain date--as we have said of the English
sparrow eating maize, of the chimney swift nesting in chimneys, and the
cliff swallow building under the eaves. But we have no such help on the
case of the red-head, which never has been without opportunities to get
birds' eggs and to kill other birds.
But there is a parallel case in another species where the date of an
acquired habit can be proved. In Florida the red-bellied woodpecker has
earned the names Orange Borer and Orange Sapsucker because he eats
oranges. It is true that he is not charged with doing damage, because
he attacks only the over-ripe and unmarketable fruit; it is known that
the habit is not general yet, for even where the birds are abundant only
a single bird or a pair will be found eating oranges, and always the
same pair, proving that it is a habit not yet learned by all of the
species; close observers declare, too, that it is but a few years since
the bird took up the habit; and, finally, we know that this must be the
case, for, though the wild orange was introduced by the Spaniards, the
sweet fruit was not extensively cultivated until recently. Here is a
habit which undoubtedly has been acquired within twenty years or so,
which will in all probability increase until instead of being the
exception it is the rule.
Why may not the red-head's occasional cannibalism, unless this is mere
individual degeneracy, and his more common custom of hoarding be habits
that he is acquiring? Why, indeed, may not the Californian woodpecker's
distinguishing trait be a habit which began like these among a few birds
here and there, wiser or more progressive than the rest, and which in
time became general and established? Why may not the two observed
instances of the Lewis's woodpecker be examples of a similar habit just
beginning? The very differences in their methods point to that
explanation. The Lewis's woodpecker that had seen the Carpenter's work
tried to imitate him; the one that lived outside his range adopted a way
of his own, unnoticed before among woodpeckers, and shelled and
quartered his nuts before he stored them.
It is remarkable that these four woodpeckers are cousins; they belong to
the same genus, and they have essentially the same structure, tastes,
and habits. Why should it be strange if their minds were alike too? if
they had a natural bent toward accumulativeness, and a natural desire to
try new wrinkles? We are sure that one of them has acquired a new habit
within a few years. Why may we not suppose as a basis and a spur to
further investigation that the others also are acquiring ways new and
strange?
XI
THE WOODPECKER'S TOOLS: HIS BILL
There is an old saying, "You may know a carpenter by his chips;" but,
though chips are seldom long absent when a woodpecker is about, can we
call the woodpecker a carpenter? Is he not both in his works and ways of
working--with the one exception of the Californian woodpecker--more of a
miner?
For the carpenter takes pieces of wood, bit by bit, and joins them
together till at last he has built a lofty skeleton or framework for his
dwelling, which last of all he covers over and closes in; and the tools
he uses are saw and hammer. With these alone he could build his house,
though it might be neither very large nor very good. When a carpenter's
house is finished, it is neither a cave nor a hole, but a pavilion built
in the open air after the model of a spreading tree,--which frames a
roof with its branches and shingles it with overlapping leaves. There is
nothing in the woodpecker's way of building which corresponds to that.
Quite different are the miner's methods. In the West, where the barren
mountain sides stretch up into snowclad summits, on the face of slopes
as seamed and gray and verdureless as the wrinkled trunk of an aged oak,
I have seen holes where human woodpeckers burrow. The entrance to a mine
half-way up a hillside looks strikingly like a woodpecker's hole and
scarcely larger. Nor does the likeness vanish as we think how in their
long tunnels inside their mountains of gold and iron and silver the
delving miners are picking and prying and picking to lengthen their
burrows just as the woodpeckers peck and pry and peck inside their
wooden mountain, the tree-trunk. Which shall we call the woodpecker--a
carpenter or a miner?
What are the miner's tools? Pick and drill, are they not? What are the
woodpecker's? The same. Certainly we shall see, if we stop to think,
that it is not a chisel that he uses, as we sometimes say. A chisel is a
knife driven by blows of a hammer; like a knife its effectiveness
depends upon the sharpness and length of its cutting edge. But a
woodpecker's bill is not a cutting tool. It is a wedge, but a wedge
working on a different principle from a knife-edge. Look at this one and
observe that, though strong and stout, it is not sharp and has no true
cutting edge. It is a tapering, square-ended, flat-sided tool, rather
six-sided at the base and holding its bevel and angles to the tip. The
woodpecker's bill is a pick, not a chisel. It is used like a pick, being
driven home with a heavy blow and getting its efficiency from its own
weight and wedge-shape and from the force with which it is impelled.
Watch the downy woodpecker at his work and see what sturdy blows he
delivers, pausing after each one to aim and drive home another telling
stroke. This is pick-axe work. But sometimes he rattles off a succession
of taps so short and quick that they blend together in one continuous
drumming, too light and quick to be likened to the ponderous swing of
the pick-axe. Now he is drilling. The work of a drill is to cut out a
small deep hole either by twirling (as in drilling metals) or by tapping
(as in drilling stone). The woodpecker drills by the latter method and
there is a curious likeness between his bill and the mason's tools.
[Illustration: 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.
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.
[Illustration: 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.
[Illustration: Diagram of right foot.]
Scientists tell us that a woodpecker's foot, though it looks so unlike a
chicken's, is really very much the same. When we ask how one of the
front toes disappeared and how the extra hind toe came to be where it
is, they tell us that there has been no addition and no loss, but the
extra hind toe is only a front toe turned backward. They call it a
_reversed fourth toe_. A bird's toes are numbered in order starting with
the hind toe and going around the _inside_ of the foot to the outer or
fourth toe. The hind toe is the thumb, and the others are numbered in
the same order as the fingers of our hands. So we see that the
woodpecker's real hind toe is rather small, like that of most birds. It
looks very much as if it had been found _too_ small and as if another
had turned back to help it do its work. Do you say that a bird cannot
turn his toes about in this way? Most cannot, to be sure, but all of the
owls can do it. An owl will sit either with two toes forward and two
backward, or with three forward and one the other way. The owls have a
reversible outer toe, and perhaps the woodpeckers did also before it
became permanently reversed.
[Illustration: Foot of Three-toed Woodpecker.]
That this is exactly what had happened is curiously confirmed. There are
a few woodpeckers in this country which have but three toes. They are
the only North American land birds with less than four toes (though many
sea and shore birds have but three). Compare this picture with a
four-toed woodpecker's foot. One toe is gone completely, when or how no
one can tell. But in some way the _first_ toe, the _thumb_, the one we
always begin to count from, has disappeared. The one left is the
reversed fourth toe, as we know by the number of joints in it.
Undoubtedly this woodpecker needed a hind toe, but he must have needed a
longer, stronger one than his natural first toe. A toe of the right
length was supplied by turning one of the front toes back, and the short
hind toe in some way disappeared.
This may seem a roundabout way to show that a woodpecker's foot is a
pair of nippers. First we studied nippers till we found out that they
were not good nippers unless they were nearly equal-limbed. Next we
studied the woodpecker'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, by 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 woodpecker's way of living, and we find by
examination that every woodpecker shows this type of foot.
There is additional evidence that this is the right explanation. Our
only other North American birds that climb on the bark of trees
professionally, 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 forward and two toes backward is confined neither to
woodpeckers nor to climbing birds. The parrots, which climb after a
fashion, have it; but so do the cuckoos, which do not climb, some of
which, like our road-runner, or ground cuckoo of the West, are strictly
terrestrial. The "yoking" of the toes may occur by the reversion of the
fourth toe, as ordinarily, or of the second toe, as in the trogons; the
arrangement appears to be definitely related to the distribution of the
tendons that control the toes. But though accounting for the structure
may give a clue to its descent, it does not justify its efficiency. The
yoke-toed foot is not exclusively a climbing foot. All our families of
climbers have at least one representative with but one toe behind, and
this clearly proves that the yoke-toed structure is by no means
necessary even though it may be an honorable inheritance among climbers.
The natural conclusion is that the important point in climbing is not
the number nor the arrangement of the toes, but the length of at least
one hind toe so as to give an equally divided foot.
There is an interesting point to notice about the woodpeckers. This
reversed fourth toe is curiously variable in length. In the flickers,
with its claw, it is a little shorter than the middle (third) toe with
its claw; in the red-heads and their friends it a little exceeds the
middle toe and claw; in the downy and the hairy it is much the longest
toe, and in the ivory-billed woodpecker it is abnormally developed. We
at once judge that it is some indication of the bird's manner of life,
and we look for it to be largest in the species that live continually
upon the trunks of trees, obtaining most of their food by drilling. We
expect to see the finest development of drilling bill accompany this
enormously developed toe, and we find them both in the ivory-billed
woodpecker. In imagination we clearly see the use of it. The great bird,
keen in his quest of grubs, sidling hastily round the tree, in an
unsteady balance and unsupported by his tail, throws one long hind toe
downward to steady himself, hooks the other into the bark above him, and
hangs between the two as firmly supported as in his ordinary position.
No doubt he does do this, but does it prove the supposition that the
heaviest and most arboreal woodpeckers have the greatest development of
the fourth toe? Not at all. There is our rare acquaintance the logcock,
or pileated woodpecker, a bird nearly as large as the ivory-billed, one
of the most persistent of our tree-climbers and more than any other
woodpecker I ever observed given to scratching rapidly round and round a
tree-trunk, clinging at ease in almost any position except
head-downward, and drilling incessantly and at all seasons for grubs; he
is a typical woodpecker of the largest size, but his hind toe and claw
are, if anything, a trifle shorter than his middle toe with its claw. He
throws it out and uses it as we have described, but it has not that
disproportion to the other toes which we expected to find as the result
of a strictly arboreal life.
What have we proved? We have not shown that the long toe is _not_ more
useful than the shorter one,--that is a matter of observation; but we
have failed entirely to show that it is so, and this can be done only in
one of two ways: either by proving that the logcock's habits are not
what all previous observers have believed them to be,--which would be
assuming a great burden of proof; or by demonstrating that his ancestry
explains why his feet do not illustrate our theory,--and this, though it
is undoubtedly the true solution, could be settled only by a very
learned man.