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Barn owl study shows they can keep gophers at bay

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Posted: Monday, May 6, 2013 7:20 am

Everyday backyard gardeners know that gophers can be a true nuisance.

But for grape growers, these root-chewing, hole-digging vermin can destroy entire fields of vines, undermining a farmer’s very livelihood.

“They burrow and dig holes. It created uneven ground and impedes drainage for the vines,” said Matt Hoffman, grower program coordinator for the Lodi Winegrape Commission.

The pests can be dealt with by chemical means — or by inviting their natural predators, barn owls, to move in.

Many landowners slap together a simple plywood box and post it on the nearest pole to encourage owls to take up residence. Farmers have used this practice for years as an inexpensive and chemical-free way to keep pest numbers low in the fields. One box can house the same breeding pair for years if there are enough pests to feed them.

“The goal isn’t to completely eradicate the gophers and voles. We don’t want to create an ecological void,” said Hoffman. “We want to keep the numbers down to a certain level.”

But one electrical company wants to make sure those poles aren’t connected to any power lines.

If an owl has made its home on a utility pole, federal law prevents the electric company from doing any work there.

PG&E provides vouchers for a free-standing plastic barn owl box designed to keep the raptors comfortable. Growers pick up the voucher, trade it in for a box and set it up in the springtime during breeding season for the owls. Very little maintenance is necessary. But they aren’t experts on owl behavior.

There are a few unanswered questions about the best way to set up the owl boxes to encourage residents.

That’s where ornithologist and former zookeeper Matt Browning comes in.

Browning is something of a barn owl expert. He started a breed-and-release program for the owls in western Pennsylvania, which introduced more than 25 owls back into nature.

Next, he tagged barn owls and tracked their migration for a year. Now his research is focused on the use of barn owls as pest management for vineyards.

On a visit to California three years ago, he met with the Lodi Winegrape Commission and started a collaborative project to figure out the best way to convince barn owls to call local vineyards home.

“The study was designed to measure the effect of a large population of barn owls on a resident rodent occupation,” Browning said.

With a $5,000 grant from PG&E, he set up 25 sturdy plastic barn owl boxes on 100 acres of land north of Lodi, and measured the rodent population.

At the end of the first year, 10 breeding pairs of barn owls had moved in and produced 44 offspring.

By the end of year two, 18 mating pairs were residents and produced 66 young.

Browning said he hasn’t gone through every scrap of data just yet, but he sees a strong suppressive effect by the barn owls on gopher numbers.

Each of those owls is eating about one gopher a night, he said. That’s more than 22,000 gophers annually. This year, the number of owls roosting in the study field has dropped, and it might be for a few reasons. It’s a pretty dry season in California, meaning there’s less wildlife. Or the study may be going so well that there aren’t enough gophers to feed such a large owl population.

“We want to show growers that barn owl boxes can be used to create a very dramatic barn owl population. They hunt relentlessly and ride the gopher population down, and they do it year after year,” said Browning.

This year, the Lodi Winegrape Commission funded two cameras to film the inside of nest boxes, and a stipend for a student team leader.

Browning thought the study would end in three years, but with enthusiastic interns from the University of California, Davis, Cosumes River College and California State University, Sacramento, it’s possible it will continue.

“This partnership with PG&E is the sort we’d like to see more of,” said Hoffman.

Contact reporter Sara Jane Pohlman at sarap@lodinews.com.

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