Invasion of the Acorn Snatchers

I’ve always thought of wild turkeys as benign, maybe even beneficial birds—not troublemakers like starlings (prime suspects in the decline of native bluebirds), or cowbirds, rudely plopping their eggs into other birds’ nests, or even the raucous crows caucusing everywhere these days, obviously up to no good. So the recent sightings of wild turkeys in the East Bay hills and flatlands—even one strolling down Solano Avenue and another in Berkeley’s People’s Park—seemed like a positive sign: at least one native (or so I thought) bird is thriving in the midst of our urban mayhem.

It turns out that California’s wild turkeys are of the Rio Grande subspecies (M. gallopavo intermedia), caught wild in Texas and brought here by the Department of Fish and Game in the 1970s and 1980s, for the benefit of hunters. It also turns out that like the rogue’s gallery of other critters and plants we’ve introduced into our unique and ecologically sensitive region, turkeys may not be so harmless.

Daniel Gluesenkamp, a restoration ecologist with Audubon, has been studying the wild gobblers since 2002 on the nonprofit’s Sonoma County Bouverie Preserve. Gluesenkamp set up two sites, each divided into two plots—one with a cage excluding turkeys, another in which turkeys were able to enter and roam freely. He added acorns and bay nuts to the plots to see how rapidly they disappeared, and used pitfall traps (cups full of a brine solution set into the ground) to capture ground-dwelling invertebrates. The difference in the sites was dramatic, says Gluesenkamp: “When we had turkeys in a plot, we lost acorns at a rate four times that of the turkey-free plot; bay nuts were lost at a rate three times the turkey-free plot, and there was a ten-fold increase in soil disturbance.”

What does that mean over time? “You get a whole bunch of bare dirt instead of nice old oak leaf litter,” says Gluesenkamp. “Some things—ruderal weeds like thistles—will probably love the soil disturbance. More sensitive native plants probably won’t.”

But even more interesting says Gluesenkamp, was what fell—or didn’t fall—into the pitfall traps. “There was a big decrease in the number of ground-dwelling invertebrates on the plots where turkeys were not excluded,” he explains. “Plots with turkeys had less [bug] diversity and became less diverse over time; the turkey-free plots were more diverse, and increased in diversity from year to year.”

Why does this matter? “The little ground-dwelling things most of us don’t even know the names of or care about are probably being impacted by wild turkeys,” he says. “It might not be important, but it might be—we just don’t know. It probably is important to whoever eats [the bugs], though.”

Gluesenkamp thinks preserving biodiversity—including all of the small things—matters a lot. “They evolved here. They’re part of the system whether we fully understand it or not,” he says. Native birds such as California quail scratch in the soil and eat these same bugs, adds Gluesenkamp. Another worry is that omnivorous turkeys—they scarf down lizards, seeds, native plants, weeds, bugs, and even occasionally smaller birds and other delicacies—could be eating rare or endangered critters like the California red-legged frog. But it’s hard to prove. It’s tough enough to find rare species, let alone observe them being eaten by a turkey, says Gluesenkamp.

Fish and Game’s wild turkey introductions of decades past were so successful that the birds are now common throughout California west of the Sierra Nevada, having successfully reproduced and expanded their range. No one knows exactly how many wild turkeys live in the state, but they could number in the hundreds of thousands, says Gluesenkamp; Fish and Game has stopped the introductions. “We do know they are increasing, and the population hasn’t leveled off yet,” he adds.

Gluesenkamp compares the turkey invasion to that of wild pigs. “There’s nothing evil or innately bad about them, but they are something we’ve introduced that disrupts the system, and if we want to keep diversity, we need to manage their populations. Hopefully we can have turkeys and calachortus.”

Meanwhile, the reintroduction of turkeys to eastern North America—where they were native before being overhunted and almost driven to extinction—is a success story up there with that of the California condor, says Gluesenkamp. “But some things aren’t meant to be everywhere,” he says, “the same way we don’t want to plant trees in something that’s supposed to be a grassland.”

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