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Repeatedly slamming your head against a tree would soon scramble your brains, but the woodpecker can do it as often as one hundred times a minute without any problems. The reason is that the woodpecker's body is perfectly designed for its unusual lifestyle. Let's examine this specialized body to see how the woodpecker can chip its way into almost any type of wood from morning to night.
Strong neck muscles provide the force behind the blow that drives the straight, hard, chisel-pointed beak into the wood. Since the head must take the impact of each stroke, the bones between the beak and the thick skull are not rigidly joined as they are in most other birds. A spongy, elastic tissue connects these flexible joints and acts as a shock absorber. Bristly feathers around the nostrils help filter out the wood dust created as the woodpecker pounds away.
Short, powerful legs connect the body to feet that can grip the side of any tree with ease. In most woodpecker species, the foot has four toes with sharply pointed, curved claws. These toes are arranged so two point to the front and two to the back. This gives the bird a firm, tonglike grip. (The three-toed species, which have only one toe pointed to the back, also manage a firm grip.)
Stiff tail feathers act as a prop to brace and steady the bird as it works. The very tips of these feathers seem to be almost elastic as they bend and spread into every tiny crack or crevice to give support on a smooth-surfaced tree or pole. The woodpecker's need for these stiff tail feathers is emphasized by its method of molting (feather replacement). The two middle feathers, which usually are quite strong and serve as the bird's main props, do not fall out until the other ten tail feathers have been replaced and once again can support the bird.
Woodpecker tongues are even more specialized, with each species having distinctive features designed for its own particular feeding requirements. In general, their tongues are long and can be extended beyond the tip of the bill. (This may not seem unusual to you, but in the bird world, only woodpeckers and hummingbirds can extend their tongues.) Most of their tongue tips are armed with backward-projecting spines or barbs that are used to impale wood-boring insects, making them easier to remove from their hidden tunnels.
The sapsucker, a member of the woodpecker family that gets its name from feeding mainly on tree sap, has no need to extend its tongue into the tree to catch insects. In place of the usual long, barbed tongue, it has a shorter tongue bristling with hairs at the tip. These hairs form a brushlike instrument just perfect for licking up sap and the occasional insect drawn to the oozing liquid.
The flicker is found on the ground more often than other woodpeckers because it feeds there. Its extra long tongue has few barbs, but it is specially adapted for lapping up ants, a major food item for the bird. Large salivary glands on each side of its mouth secrete a sticky mucous coating for the tongue. When the flicker extends its long tongue into an anthill or along a well-traveled ant trail, the insects rush to attack what looks like an invading worm. They are caught by the sticky mucus and are quickly eaten.
But where does the flicker put such a long tongue when it is not extended catching ants? The tongue is divided into two branches at the rear, but instead of being attached to the bottom of the skull as in most birds, these branches pass on either side of the windpipe. Lengthened by two bony ligaments, they slide up over the skull (beneath the skin, of course), come together at the forehead and extend down into the right nostril. As easily as a knife slips in and out of its sheath, the woodpecker's tongue glides smoothly along its path over the skull as the bird flicks it in and out while feeding. Depending upon the species of woodpecker, the back of the tongue ends at the base of the bill, in the upper beak, or, rarely, behind or below the eye. In any case, the woodpecker has part of its tongue on top of its head.
The woodpecker's strong beak and barbed tongue are a great combination for getting rid of insect pests living beneath the tree bark. However, without its excellent hearing, the bird would not be very good at locating its prey. The evidence of this can be seen in the following account by a forester. "I once saw a pileated woodpecker fly to a tough old hickory tree in which ants were using a little knothole as their entrance. The bird didn't drill in this obvious place. Instead, it circled the trunk, gently tapping, then pausing. Finally it proceeded to whack into the very heart of the ant nest – five feet below the knothole."
We do not know whether the bird heard the movements of the disturbed insects or was able to distinguish subtle differences in the tapping sound caused by the ants' hollowed-out tunnels and nest. However, we do know that something pinpointed the spot where further investigation was needed and, since the bird cannot boast x-ray vision, it is fairly safe to assume that the woodpecker's hearing played a major role in locating the ant nest.
Some people believe all woodpeckers are destructive pests because they chip holes into trees looking for food. But by stripping the bark from a dead or dying tree and eliminating the resident populations of carpenter ants or wood-boring grubs and insects, the woodpecker actually helps to prevent the spread of these destructive creatures to healthy trees nearby.
The story is told of a man who awoke one morning to find a woodpecker hammering away at his favorite oak tree. Thinking that he was protecting the tree, he chased away the bird and covered the riddled part of the tree trunk with wire mesh. Bright and early the next morning the bird was back. Persistent pecking reduced the wire mesh to tatters and the bird resumed its drilling into the oak. The man continued to harass the bird until the woodpecker finally gave up and flew away. The man congratulated himself for saving his prized oak from the bird. Time, however, proved him wrong. A few years later, during a severe storm, the tree trunk snapped at the spot where the woodpecker had been drilling. An examination revealed that a colony of carpenter ants had riddled the seemingly healthy tree with a maze of galleries and tunnels. If the woodpecker had been allowed to continue its drilling, the ant nest probably would have been eradicated and the tree saved from the unseen destruction lurking within.
In addition to the wood-chiseling activities associated with feeding, all woodpeckers use their beaks to chip out a nesting cavity of some type in a tree, stump, telephone pole, fence post, or other such wooden object. Their white, unmarked eggs are laid on a bed of wood chips and splinters in the bottom of the cavity. Both parents feed the young, pumping them full of predigested food until they are able to forage for themselves.
Other than a rattling, cackling call, which can hardly be called singing, woodpeckers communicate with each other by drumming. The sound is made by rapidly striking the beak against a hollow tree trunk, dead branch, tin roof, garbage can lid, or other resonant object. This drumming serves as a warning to territorial trespassers and is used to attract a mate.
When one woodpecker's drumming was analyzed with special recording equipment, it was discovered that the bird produced 500 to 600 two-second bursts of sound a day. Each two-second burst contained as many as forty rapid blows. In some species the tapping is so varied it sounds like a complicated code. These tapped conversations take place between the male and female throughout the courting and nesting. Each coming and going from the nest is accompanied by the proper number and sequence of strokes.
The next time you hear a woodpecker's jackhammerlike blows you will know it is either talking, feeding, or building a home. Whichever the bird is doing, it is filling its niche in the woodland environment.
1989 – Woodpeckers: Introducing Birds to Young Naturalists. The Louise Lindsey Merrick Texas Environment Series, No. 9, pp. 32-34. Texas A&M University Press, College Station.