Wings on the River: Who can eat poison oak berries?

Some birds can tolerate the toxins with which poisonous plants protect themselves from herbivores. Thus, both the plant and bird benefit — the bird fills its stomach, and later deposits the seeds unharmed in a little splot of fertilizer.

But poison oak isn’t toxic to wildlife — turns out, humans just happen to have an allergy to Toxicodendron diversilobum’s potent microbe-repellent compound.

According to Mendocino County Recreation District, up to 45 species of birds forage the numerous tiny, greasy-white berries of this resilient native plant.

Similar to the equally nasty poison ivy, found in moister regions west of the Cascades, poison oak thrives in recently disturbed, dry ground in the Pacific Northwest, from Washington through California. It’s wise to recognize those three-lobed, glistenining-green leaves — and resist the temptation to pick a bouquet when they turn a marvelous salmon-pink, crimson and scarlet in September!

If a human ate poison oak berries, they’d get very sick indeed. That’s because the berries are imbued with urushiol, a compound that causes contact dermatitis in about 90% of humans. Touching the oily-looking stems and leaves, even petting a cat or dog that’s sniffled the plant, can apply a two-week blistering rash that will (I speak from experience) become your summer’s nightmare.

Here in the Gorge, I’ve seen Yellow-rumped Warblers, Downy Woodpeckers, Black-Capped Chickadees, Hermit Thrushes, Red-shafted Flickers, those kinglets and Stellars Jays eating poison oak. Notes and photos from other birdwatchers add sparrows, towhees, robins, grosbeaks and wrentits to the list.

In hard winters, when all other plants are eaten up or frozen beneath an icy crust, I find the sharp upright sticks of poison oak with their buds neatly crunched off. Apparently, our local black-tailed deer (and livestock) can eat poison oak just fine — but I don’t see them eat it as much as rain-softened lichen or dessicated poplar leaves.

Lucky humans: We, and a few other primates, are the only critters with a known allergy to urushiol, a substance scientists think may protect the plant against microbes. When it binds to proteins in the membranes of your skin cells, those cells can no longer recognize each other as part of you — they start attacking and killing each other. When wildfires burn poison oak, inhaling urushiol smoke can be dangerous.

Given those dangers, if you get long-handled pliers and trim it back from the paths, the plant is surprisingly easy to live with — and it’s a life-giving resource for some of the most interesting winter birds, like that tiny Ruby-Crowned Kinglet with its hidden scarlet topknot and two-note “button-click” call.

Indigenous peoples also had medicinal uses for the plant, according to the National Park Service — everything from basket-weaving to tattooing.

So poison oak has a good side. On a cold, snowy winter day — with the rashes of summer healed — it’s a joy to watch tiny kinglets and chickadees bounce and bob as they struggle to tear a giant, fat, juicy toxic fruit from its stem, filling their stomachs in the leafless woods.

One good identification and medical resource is extension.oregonstate.edu/catalog/pub/pnw-108-pacific-poison-oak-western-poison-ivy-identification-management.