Sunday, January 3, 2010

In the woods... Acorn Woodpecker

Acorn WoodpeckerAcorn Woodpecker, Forest Grove, Oregon on 2 January 2010 by Greg Gillson.


Four noisy birds emerged from the hole in the old oak tree, pictured above. These birds are resident at Pacific University in Forest Grove, Oregon. This woodpecker colony, west of Portland, is the most well-known location of these birds in the Pacific Northwest. This fact is perhaps surprising as this location is nearly as far north as these striking woodpeckers live.

A small colony is along the Columbia River near Lyle, Washington, across from The Dalles, Oregon. Otherwise, in the Pacific NW, this species can only be found in western Oregon and NW California. From there it occurs south through California. Other populations occur from southern Utah, southern Colorado, and Texas, south through Mexico, to northern South America.

Each colony of these woodpeckers is an extended family. They work together to care for their stash of acorns, wedged into the bark or dead limb of their granary trees. The acorns are inserted while green and shrink as they dry. Thus the woodpeckers are constantly tending their larder, testing whether the nuts are still tight. If not, squirrels will steal them. So they must fit every loose acorn to a new hole.

Throughout most of their range in North America these birds rely on having several species of oak trees available. Oak species tend to fluctuate in acorn productivity from year to year. So having more than one species of oak increases the chance that one or both will be productive. In the Willamette Valley of western Oregon, however, the only oak available is the white oak. Somehow these woodpeckers are thriving after extending their range here in the second half of the 20th century.

With white wing and rump patches, and a clown face and loud whack-up, whack-up call, they are unlikely to be mistaken for any other woodpecker.

1 comment:

  1. I have four of these that come to visit my feeder often in Mcminnville. Thanks for the info on them!