The next time you hear a tapping sound in the woods, consider the importance of birds that do construction work.
Window On Nature
By Lowell & Kaye Christie, F47166
Just like us, wild critters need a safe location to live and raise a family. Many small birds and mammals solve the dilemma by choosing a home built by the master carpenters of the bird world, the woodpeckers. Fortunately for them, most woodpeckers use a nest hole for only a single season, leaving a vacancy for those with more limited construction skills.
Small owls and other birds; bats; squirrels; and even bees have been known to take over an abandoned woodpecker nest while the original occupant goes on to do what it does best — pecking away at another tree. These members of the Picidae family are uniquely adapted to using their beaks for building homes and also in foraging for food.
Of the 200-plus species of woodpeckers in the world, approximately 20 species live in North America. We’re a little hesitant to give an actual number because of the dispute over whether the ivory-billed woodpecker, which is supposedly extinct, has been sighted recently. The ivory-billed was once the largest woodpecker on the continent, measuring roughly 20 inches long.
Ignoring the ivory-billed, North American woodpeckers range in size from the pileated (usually pronounced PIE-lee-ay-ted), which is about the size of a crow, down to the little 1-ounce downy woodpecker, whose average length is only 6 1/2 inches. The downy may be the smallest, but it’s also the most common of the woodpeckers.
Most people know that woodpeckers drill holes with their beaks, either from seeing them in action or perhaps from watching the cartoon image of Woody Woodpecker (who was modeled after the pileated). But few understand the complexity of the structure that allows that beak to get banged against a relatively unyielding block of wood at speeds as high as 15 or 20 times per second (for short periods), and perhaps totaling 12,000 individual pecks in a day. The force of a single peck has been compared to that created by a human running into a tree face-first at a speed of 16 miles per hour.
The bird’s bill is a wedge-edged pecking and prying device with a horny sheath that grows rapidly as the front edge wears away. This keeps the tip of the bill sharp even with the constant beating it takes from hitting wood at high speeds. At the other end of the bill, a layer of shock-absorbing tissue attaches to the bird’s skull. The bones of the skull are made of a thick but somewhat spongy material, so the constant pounding doesn’t cause it to crack.
While pecking, a woodpecker must maintain an erect posture so it can hit its target at a precise right angle. Anything else might result in a sideways rebound that could actually detach the bird’s bill from its skull. For stability, the bird creates a tripod between its two feet and its tail, which contains a pair of stiff central feathers that press against the trunk of the tree. These tail feathers are so important to the woodpecker that they are not molted until the replacement feathers have fully developed.
The bird’s neck and shoulder muscles are much larger than those in other birds. Just a millisecond before impact, these muscles tense and deflect the force of the blow to the sides and base of the skull, protecting the bird’s brain. High-speed photography has shown that as the woodpecker makes impact, it closes its eyelids, which keeps the eyeballs under pressure so the retinas can’t move, and also protects the eyes from flying wood chips.
When foraging for food, the woodpecker will often give light taps on the tree trunk or branches, listening to the sound produced as it searches for tunnels created by wood-boring insects. When it hears the hollow sound of a tunnel, it switches to its more powerful digging taps to chip through the outer layers of bark.
Many woodpecker species have long tongues to help them extract prey from these wooden cavities. The tongue has bristles and is covered with sticky saliva, making it easy to capture insects, especially since some of the birds can extend their tongues as much as two inches beyond the tips of their bills.
Not all of the woodpecker tribe has these modifications to the same degree. Flickers and sapsuckers are woodpeckers, but they go after dinner in different ways. Flickers are most often found on the ground searching for ants. Sapsuckers drill small holes about the diameter of a pencil in the trunks of trees (they can drill as many as 50 holes an hour), and return later to lap up the syrupy sap, along with any insects it has attracted.
The acorn woodpecker, which lives in the western part of the continent, also drills many small holes, not to find food, but to store it. This woodpecker lives in extended families, and as a group they drill hundreds of holes in the dead wood of a standing tree. Into each hole they’ll insert a single acorn that will become part of the family’s food supply in winter.
Sometimes the activity of woodpeckers conflicts with humans, as they make holes where we don’t think they belong. Telephone poles in this bird’s range can become granaries holding thousands of acorns. The weakened poles eventually have to be replaced.
During the spring, an enterprising woodpecker may discover that drumming on a portion of a house creates the perfect sound to attract a mate. Back in 1995 some woodpeckers decided to drill more than 200 holes in the foam covering of the fuel tanks of the Space Shuttle while it was on the launching pad. Not surprisingly, the launch was delayed.
For the most part, however, woodpeckers stick to their own business, with flickers eating ants on the ground, sapsuckers making the rounds to harvest their liquid meals, and the master builders creating homes for themselves and those that depend on them. Woodpeckers are entertaining to watch, fairly easy to find because of the racket they make, and an important part of our natural world.