Home & Garden Columns
The week before the Fourth of July we were up at Lassen Volcanic National Park watching the traffic at Hat Lake. The place was jumping.
A male western tanager, resplendent in red and yellow, came down to the lake’s edge to drink. Audubon’s and Wilson’s warblers flashed in and out of the young lodgepole pines. A dipper made repeated shuttle flights from its nest below the highway bridge, alternately ducking underwater to forage or swimming like a little duck as it retrieved insects—mayflies?—from the lake’s surface. Another hard-working parent, a male white-headed woodpecker, commuted between its tree-cavity nest and some beetle-rich dead snag nearby. Tree swallows skimmed low over the lake, and noisy young spotted sandpipers chased each other around the beaver lodge.
No beavers, though. The last time we were there, we watched them late into the buggy twilight as they cruised the lake they had made, or at least augmented. This time the dam was in poor repair, and the lodge was surrounded by mud. We blamed that on the dry winter, but were still worried about the beavers. Later a ranger-naturalist told us they were gone. One had been found dead on the highway last year; another on a hiking trail—disease, old age, who knows.
Maybe another pair will wander up from the Warner Valley and take over the franchise. If not, the lake will inexorably change, and the results of all that dedicated beavering will be gone. And everything in and around it—the tanagers, the woodpeckers, the mayflies, the pines—will be affected, one way or another.
Some years back, before he took on organized religion, Richard Dawkins wrote a book called The Extended Phenotype. A phenotype is the physical manifestation of a genotype—the ensemble of physical traits that the genome codes for. Dawkins’ point was that you have to think of behavior as part of that ensemble, which is fair enough with beavers. Their dam-building drive is so hard-wired that if you play the sound of running water for captives, they’ll pile up sticks and brush in front of the speaker.
Beyond that, Dawkins’ notion of the phenotype also includes the built environment that results from an organism’s behavior—the dam, the pond, the lodge.
We tend to think of our species as the only one that leaves a significant mark on the world, for better or worse. Far from it: beyond the engineering of beavers, consider the cities of the termites or the coral polyps, the soil moved by pocket gophers. All of us, man to microorganism, shape our various environments.
And our environments shape us back. Another book from the ’80s, Richard Levins and Richard Lewontin’s The Dialectical Biologist, tried to make that point, albeit with too much Marxist jargon for most tastes. (With us, there’s another layer when culture feeds back into the genome, as when Northern European and East African cattle herders independently—by separate genetic pathways—evolved adult lactose tolerance.)
Woodpeckers—to pick just one of the cast of characters at Hat Lake—are builders and shapers in their own right. Their nesting cavities provide housing for a whole community of hole-nesting birds: chickadees, nuthatches, flycatchers, swallows, wrens. A woodpecker neighborhood tends to have high avian diversity. Small mammals like flying squirrels also
adopt old woodpecker nests.
But it doesn’t stop there. Working in Lassen National Forest, not far from where we were, Kerry Farris and Steve Zack of the Wildlife Conservation Society and Martin Huss of Arkansas State University made an interesting discovery about woodpeckers. They mist-netted white-headed, hairy, and black-backed woodpeckers, swabbed their beaks, and cultured the contents of the swab in a petri dish. Half a dozen species of filamentous fungi, some known wood-decayers, were identified in the culture.
The woodpeckers seem to be carrying around little fungus colonies, inoculating the ponderosa pine snags where they feed with organisms that hasten the decay of the dead wood, making the birds’ foraging routines a little easier. Other cavity nesters like red-breasted nuthatches and mountain chickadees had their own fungus cultures; a control group of non-cavity-nesters—warblers, kinglets, tanagers, finches—did not.
The jury is still out on whether what’s going on with the woodpeckers and the fungi is dedicated mutualism or opportunistic hitchhiking, and who is part of whose extended phenotype. The more you look at the interface of ecology and evolution, the more complicated it seems to get.
Photograph by Ron Sullivan,
A male white-headed woodpecker at Hat Lake, Lassen Volcanic National Park.
Joe Eaton’s “Wild Neighbors” column appears every other Tuesday in the Berkeley Daily Planet, alternating with Ron Sullivan’s “Green Neighbors” column on East Bay trees.