Our Window on Nature

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Acorn Woodpecker – Master Carpenter

Filed under: Birds — Lowell Christie -- January 28, 2007 @ 4:58 pm

Acorn GranaryAcorn woodpeckers leave very little to chance. Pessimists by nature, these birds devote their waking hours to storing insects and acorns from late summer through fall, making sure that they’ll have ample food for the coming winter.

In much of California and the Southwest, you can’t help seeing or hearing acorn woodpeckers. They’re common wherever you find a mixture of oaks, junipers, and pines. You won’t have to look hard for them either, because they’ll be sharing your backyard or campground. These birds rank among the noisiest of the woodpecker tribe, and their loud “jacka, jacka, jacka” announces their presence long before you spot the clownlike pattern of their facial feathers. More than most birds, they seem to take pleasure in the sound of their own voices.

Of course, they have a lot to discuss. Whereas typical woodpeckers move about in pairs, acorn woodpeckers live in groups of six to a dozen or more. It takes a lot of hemming and hawing, screeching and cawing to live, work, and raise young in close quarters.

As one might expect, such communal living produces distinctive behavior patterns. The most noticeable – and perhaps the most interesting – of these behaviors is the acorn woodpecker’s habit of storing food in communal granaries.

All North American species of woodpeckers are woodworkers, but none approaches the efforts that acorn woodpeckers make to build and stock their community larder. Find a dead snag in acorn woodpecker country, and it’s apt to be so riddled with holes that it looks like a sponge.

Given enough time and enough birds, acorn woodpeckers will change a branch into a honeycomb of one-inch holes, all just large enough to hold a few beetles or an acorn. The building and storage cycle begins with spring housecleaning. Acorns work cooperatively to clean out the debris from the previous year before they settle down to add a few dozen, or a few hundred, new cells. They’ll spend the rest of the summer and fall stocking the holes with enough food to live off of throughout much of the winter.

We’ve found some masterfully built granaries over the years, especially in Arizona, but nothing we’ve seen compares with the masterpiece that was found and documented back in the 1920s. One California sycamore tree reportedly held an incredible 20,000 cells.

Oddly enough, the granaries don’t appear to affect the health of the tree much, mostly because the holes are chiseled into dead wood. And when there is plenty of wood available, the birds can spread out to peck on several trees, fence posts, and an occasional power pole. It’s only when acorn woodpeckers become overexuberant about nest building that they inflict more than cosmetic damage.

Nobody fusses much when there are numerous acorn nest holes in a single tree, but utility company officials become more than a little irritated when the birds focus their efforts on power poles. For a bird, an electrical or telephone post is merely a tall tree without branches, and it makes an admirable home. But the birds have been known to riddle these poles with so many nest cavities that the wood snaps in a heavy wind. Replacing the pole with a new one costs power companies several thousand dollars in materials and labor. Besides, this measure often merely provides the woodpeckers with a nice new pole to peck on.

So, in an effort to prove that man can outsmart, outmaneuver, or outwit a nine-inch bird the companies have tried wrapping the more popular poles with metal (which is dangerous, since it conducts electricity) or plastic mesh (which is expensive, and faulty, because the plastic rots in the sun). They’ve tried woodpecker repellents and even attaching rubber snakes that appear to be climbing up the pole. So far the most promising method has been to fill the nest cavities with rocks and gravel and then inject epoxy into the air spaces between the rocks. This strengthens the pole enough so that it can withstand a few more holes. Ultimately, however, the woodpeckers always win.

All woodpeckers are interesting to watch, yet the acorn is the most fascinating of all, because this species is so tame and so vividly marked. You can relax and rest beneath the very tree that these woodpeckers are filling with acorns – or coming to for a meal. Males and females are clad basically alike, with iridescent black bodies and wings, marked by a white rump patch and wingspots, and a dingy white breast. The black-and-white face of an acorn woodpecker is dramatically marked with a red cap (on the male) and brilliant white eyes. They’ll also be seen flying overhead, if the day is warm enough for insects to be buzzing about. Acorn woodpeckers catch insects on the wing much as flycatchers do, although not as gracefully. And of course, they do none of it quietly.

With all of the stored wealth that these birds protect, it’s no surprise that they are very territorial. Only members of their own group are tolerated anywhere near the granary or the nest. Anyone else gets a hostile reception. This doesn’t mean that squirrels, jays, and even other bands of acorns won’t try a sneak attack; however, such raids seldom produce much booty. A band of acorn woodpeckers doesn’t go to the trouble of producing a huge storehouse and stocking it with food with the intention of sharing it with others. Nature isn’t altruistic; in the animal world it’s every bird and mammal for itself, and acorn woodpeckers are no exception.


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