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Woodpeckers Give People Headaches, But Not Themselves

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Illustration by Adelaide Tyrol

Spring having arrived, people can expect to be jolted from their early morning sleep by an outrageous burst of hammering on the side of the house. Their rude awakening is not the work of some nightmarish carpenter gone berserk, but merely a bird, one of our several species of woodpeckers engaging in the behavior known as drumming. But why drum?

Woodpeckers are superbly evolved to find food and make nest cavities by excavating into trees with their beaks. Somewhere along the way they also began using the blows to make sound. Modern-day woodpeckers use drumming on resonant surfaces as most other birds use song – to communicate. Ornithologists believe that woodpeckers drum to claim territory and to attract and strengthen bonds with mates. The trunk or limbs of dead trees resonate nicely, but the siding, trim or metal chimney on your house may be even better. Drumming usually is not seriously damaging, though it can leave clusters of small dents in wooden surfaces.

In our area we may encounter, in order of increasing size, the downy woodpecker, hairy woodpecker, northern flicker and pileated woodpecker. All these birds produce intense drum rolls, a repeated hammering at a rate of 18-26 beats per second. You may also have heard from the yellow-bellied sapsucker, another type of woodpecker that drums but in its case with less gusto. Their sounds start with closely spaced beats that soon trail off. Sapsuckers, unlike most other woodpeckers, do not excavate in trees for food. Instead they bore rows of small holes into trees, often birches or apples, to drink the sap that then leaks out. They do this by licking, not by ‘sucking,’ with their brush-like tongues. They will also feed on insects on the surface of tree bark. A sapsucker’s holes can damage a tree’s health, so orchardists often wrap trunks of their trees with mesh or burlap to deter the bird.

Downy, hairy, and pileated woodpeckers often can be seen methodically tapping their way along tree trunks or limbs. In such cases they are looking for food, not broadcasting their presence. They peck and listen for differences in resonance to locate the tunnels of their prey, usually wood-boring grubs. Once a tunnel is found the woodpecker excavates a feeding hole using its whole body to deliver heavier, chisel-like blows to free chunks of wood. Scientists estimate that a woodpecker may strike its bill some 12,000 times in a day, enduring deceleration forces of up to 1,200 times the force of gravity with each blow. That’s like hitting a tree face-first at 16 miles per hour. How do they do this without suffering a skull fracture, brain damage or detached retinas?

Nature has equipped woodpeckers with thick yet spongy skull bones, so their skull can withstand tremendous pounding without cracking. The skull, and the brain, also benefit from a cushion of cartilage located where the skull meets the jawbone. The jawbone attaches to the skull through powerful muscles that contract a millisecond ahead of each strike, forming a resilient unit that transmits and deflects the full brunt of the blow to the sides and base of the skull.

Finally, the woodpecker’s brain is held tightly against the skull, so there is no room to slap about and become damaged.

As for retina protection, high-speed photography has revealed that woodpeckers close their thick, muscular eyelids an instant before each strike. This keeps their eyeballs under pressure, so the retina can’t move, while also protecting against flying splinters.

Once a woodpecker has excavated into a grub’s tunnel, it extracts its prey using its tongue, a long and extraordinary device. Woodpeckers, like other birds, have a flexible bone in their tongue called the hyoid. The special bone is Y-shaped, with the tail of the ‘Y’ inside the tongue. The two arms of the ‘Y’ are greatly elongated in woodpeckers, curving back around each side of the skull, allowing a woodpecker to deploy its tongue with great strength. Their tongue has bristles covered with sticky saliva, making it a formidable insect-trapping tool.

Downy, hairy and pileated woodpeckers, after pairing up in early spring, begin excavating their nest sites in the trunk of a living tree that’s usually afflicted with heart rot. The birds peck through a few inches of solid wood before excavating downwards in the tree’s core. Nests of hairy woodpeckers may run 12-16 inches deep, while those of the pileated woodpecker may be two feet deep. Creating the cavities is hard work and can take days to complete.

And their labor can serve other wildlife, such as flying squirrels, which will move into abandoned nests, and other cavity-nesting birds that cannot easily peck holes – such as, nuthatches, chickadees, titmice and house wrens.

A dead or dying tree with woodpecker holes is a good find for these birds, offering ready-made shelters and multitudes of insects just waiting to be eaten.

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