A single borer may kill a tree; so, too, may a few beetles; while a small number of weevils will injure and stunt a tree so that it is left an easy victim for other insects. Borers, beetles, and weevils are among the worst enemies of trees. They multiply with astounding rapidity and annually kill millions of scattered trees. Annually, too, there are numerous outbreaks of beetles, whose depredations extend over hundreds and occasionally over thousands of acres. Caterpillars, moths, and saw-flies are exceedingly injurious tree-pests, but they damage the outer parts of the tree. Both they and their eggs are easily accessible to many kinds of birds, including the woodpeckers; but borers, beetles, and weevils live and deposit their eggs in the very vitals of the tree. In the tree's vitals, protected by a heavy barrier of wood or bark, they are secure from the beaks and claws of all birds except Dr. Woodpecker, the chief surgeon of the forest. About the only opportunity that other birds have to feed upon borers and beetles is during the brief time they occupy in emerging from the tree that they have killed, in their flight to some live tree, and during their brief exposure while boring into it.
Beetles live and move in swarms, and, according to their numbers, concentrate their attack upon a single tree or upon many trees. Most beetles are one of a dozen species of Dendroctonus, which means "tree-killer." Left in undisturbed possession of a tree, many mother beetles may have half a million descendants in a single season. Fortunately for the forest, Dr. Woodpecker, during his ceaseless round of inspection and service, generally discovers infested trees. If one woodpecker is not equal to the situation, many are concentrated at this insect-breeding place; and here they remain until the last dweller in darkness is reached and devoured. Thus most beetle outbreaks are prevented. Now and then all the conditions are favorable for the beetles, or the woodpecker may be persecuted and lose some of his family; so that, despite his utmost efforts, he fails to make the rounds of his forest, and the result is an outbreak of insects, with wide depredations. So important are these birds that the shooting of a single one may allow insects to multiply and waste acres of forest.
During the periods in which the insects are held in check the woodpecker ranges through the forest, inspecting tree after tree. Many times, during their tireless rounds of search and inspection, I have followed them for hours. On one occasion in the mountains of Colorado I followed a Batchelder woodpecker through a spruce forest all day long. Both of us had a busy day. He inspected eight hundred and twenty-seven trees, most of which were spruce or lodge-pole pine. Although he moved quickly, he was intensely concentrated, was systematic, and apparently did the inspection carefully. The forest was a healthy one and harbored only straggling insects. Now and then he picked up an isolated insect from a limb or took an egg-cluster from a break in the bark on a trunk. Only two pecking operations were required. On another occasion I watched a hairy woodpecker spend more than three days upon one tree-trunk; this he pecked full of holes and from its vitals he dragged more than a gross of devouring grubs. In this case not only was the beetle colony destroyed but the tree survived.
WOODPECKER HOLES IN A PINE INJURED BY LIGHTNING
Woodpecker holes commonly are shallow, except in dead trees. Most of the burrowing or boring insects which infest living trees work in the outermost sapwood, just beneath the bark, or in the inner bark. Hence the doctor does not need to cut deeply. In most cases his peckings in the wood are so shallow that no scar or record is found. Hence a tree might be operated on by him a dozen times in a season, and still not show a scar when split or sawed into pieces. Most of his peckings simply penetrate the bark, and on living trees this epidermis scales off; thus in a short time all traces of his feast-getting are obliterated. I have, however, in dissecting and studying fallen trees, found a number of deep holes in their trunks which woodpeckers had made years before the trees came to their death. In one instance, as I have related in "The Story of a Thousand-Year Pine" in "Wild Life on the Rockies," a deep oblong hole was pecked in a pine nearly eight hundred years before it died. The hole filled with pitch and was overgrown with bark and wood.
Woodpeckers commonly nest in a dead limb or trunk, a number of feet from the ground. Here, in the heart of things, they excavate a moderately roomy nest. It is common for many woodpeckers to peck out a deep hole in a dead tree for individual shelter during the winter. Generally neither nest nor winter lodging is used longer than a season. The abandoned holes are welcomed as shelters and nesting-places by many birds that prefer wooden-walled houses but cannot themselves construct them. Chickadees and bluebirds often nest in them. Screech owls frequently philosophize within these retreats. On bitter cold nights these holes shelter and save birds of many species. One autumn day, while watching beneath a pine, I saw fifteen brown nuthatches issue from a woodpecker's hole in a dead limb. Just what they were doing inside I cannot imagine; the extraordinary number that had gathered therein made the incident so unusual that for a long time I hesitated to tell it. However, early one autumn, Mr. Frank M. Chapman climbed up the mountainside to see me, and, while resting on the way up, he beheld twenty-seven nuthatches emerge from a hole in a pine.
By tapping against dead tree-trunks I have often roused Mother Woodpecker from her nest. Thrusting out her head from a hole far above, she peered down with one eye and comically tilted her head to discover the cause of the disturbance. With long nose and head tilted to one side, she had both a storky and a philosophical appearance. The woodpecker, more than any other bird of my acquaintance, at times actually appears to need only a pair of spectacles upon his nose in order fully to complete his attitude and expression of wisdom.
The downy woodpecker, the smallest member of a family of twenty-four distinguished species, is the honored one. He is a confiding little fellow and I have often accompanied him on his daily rounds. He does not confine his attacks to the concealed enemies of the trees, but preys freely upon caterpillars and other enemies which feast upon their leaves and bloom. He appears most content close to the haunts of man and spends much of his time caring for orchards and cleaning up the shade trees. One morning in Missouri a downy alighted against the base of an apple tree within a few feet of where I was standing. He arrived with an undulating flight and swept in sideways toward the trunk, as though thrown. Spat! he struck. For a moment he stuck motionless, then he began to sidle round and up the trunk. Every now and then he tapped with his bill or else stopped to peer into a bark-cavity. He devoured an insect egg-cluster, a spider, and a beetle of some kind before ascending to the first limb.
Just below the point of a limb's attachment he edged about, giving the tree-trunk a rattling patter of taps with his bill. He was sounding for something. Presently a spot appeared to satisfy him. Adjusting himself, he rained blows with his pick-axe bill upon this, tilting his head and directing the strokes with an apparently automatic action, now and then giving a side swipe with his bill, probably to tear out a splinter or throw off a chip. In six minutes his prey was evidently in sight. Then he enlarged the hole and slightly deepened it vertically. Pausing, he thrust his head into the hole and his bill into a cavity beyond. With a backward tug he pulled his head out, then his bill, and at last his extended tongue with a grub impaled on its barbed point. This grub was dragged from the bottom of a crooked gallery at a point more than three inches beyond the bottom of the pecked hole. A useful bread-getting tool, this tongue of his,—a flexible, extensible spear.