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Controlling Voles

Crop damage from voles leads UI Extension to explore alternate control methods

One of the first issues Jason Thomas faced as an educator with University of Idaho Extension was small in size, but large in impact. Growers in Minidoka County alerted Thomas to their constant battle with voles — a small rodent that feeds on seeds, roots, stems and leaves of various crops.

Since most of his agricultural work had been in Texas and Indiana, Thomas wasn’t aware of how big of an impact voles have on crops in some parts of Idaho.

“I went out to one of the farmers’ fields and it looked decimated,” Thomas said. “I was amazed at the amount of holes in the ground. It looked almost like 10 to 20 percent of the field was these mounds from voles.”

In Idaho, voles feed on everything from bushes, lawns and trees, to alfalfa, wheat, potatoes and sugar beets, creating serious problems for homeowners and growers. Most growers rely on rodenticides to control populations, however, the poison used in most products is potentially toxic to other animals and to humans. And, if the rodenticides aren’t applied at the right time, they aren’t always effective.

“It’s a very expensive, costly practice in my opinion and as to how that affects the environment and other birds and animals, there is still a lot of work that needs to be done on that,” Thomas said.

Alfalfa field with multiple holes and mounds of dirt
A field of alfalfa shows damage made by voles.

Looking for Alternatives

Thomas began investigating alternative control methods that were more environmentally — and economically — friendly. He discovered research projects in California using natural predators to control vole populations — specifically barn owls.

“With the barn owls, the hope is when we have really bad vole years, they’re eating enough that you’ll think twice about putting out the rodenticides because they are at least helping with the population,” Thomas said. “Most farmers know about hawks and falcons that will come in and kill rodents, but barn owls are going to be working at night, so an extra set of predators out there helping out.”

Barn owls are native to Idaho but require cavities for nesting. So, open agricultural fields aren’t the best location for them. Enter UI Extension and the barn owl box project.

Barn owl in hay pile
A female owl nests in a hay pile in Paul, Idaho.

Providing a Good Home

Thomas and fellow UI Extension educators Joel Packham, Terrell Sorenson and Jacob Rickman are working with growers to install barn owl boxes in their fields. Data will be collected from the boxes where owls are nesting.

Thomas recommends that the boxes be installed at least eight feet off the ground and with the front facing north. They should also be at least 1,000 feet apart, the approximate territory that barn owls defend. Boxes must also be cleaned out once a year.

“We want to provide for them a good home where they can live — that’s the big thing to me,” Thomas said. “There’s no habitat for them to live and nest except for getting into a person’s barn or hay pile and then they get interference from humans.”

The team is partnering with local area youth to produce the boxes.

“We help build them but we also use it as a way to teach kids about the environment and the barn owls,” Thomas said. “In Power County they use this with the sixth grade as part of their curriculum about wildlife. We’re also in the works to get some help from Eagle and Boy Scout projects and maybe some 4-H youth. This is a real world project that is making a difference in the community.”

Wooden box with hole in upper left corner
An example of the barn owl box produced by UI Extension educators and partners.
Two men on ladders attaching box to pole
UI Extension educator Jason Thomas installs a barn owl box at the home of a local producer.

Research on Effectiveness

Thomas and his colleagues will monitor the boxes over the next few years. The team is able to record activity and count babies by using small cameras mounted to poles that are inserted into the boxes. The team will also analyze owl pellets for skulls to make estimates on how many voles the owls are feeding on.

Thomas plans to do a study comparing areas with heavy barn owl nesting versus no boxes, the amount of rodenticides used in each area, and the amount of vole damage. He also hopes to provide estimates on how much money can be saved through the use of barn owls and reduction of rodenticides.

“We want to show that it does have an impact and can help with the vole populations,” Thomas said. “The hope is, those really high years we can keep it lower with the barn owls. If we can get enough data on how much folks are spending on rodenticides each year with or without barn owls then we’ll estimate the amount of savings. It’s relatively cheap to put up one of these barn owl boxes.”

Thomas currently has around 45-50 boxes deployed in farmers’ fields and is pushing to add more during October and November in preparation for next year’s mating season.

“The end goal is that a lot more farmers are using barn owls and understand that we can use the environment to our advantage,” Thomas said. “Even if that’s all that changes, farmers start thinking about how they can use the environment to their advantage and not always turn to rodenticides or chemicals, then that would be a big win for us.”

There is currently a waitlist for pre-built barn boxes but instructions for building your own box are available.

Man speaking into microphone, woman holding barn owl
UI Extension educator Jason Thomas discusses the barn owl project with citizens at the Minidoka County Fair.

Article by Amy Calabretta, College of Agricultural and Life Sciences

Photos by Jason Thomas, University of Idaho Extension

Published in October 2019

University of Idaho Extension

Physical Address:
E. J. Iddings Agricultural Science Laboratory, Room 52
606 S Rayburn St.
Moscow, ID

Mailing Address:
University of Idaho Extension
875 Perimeter Drive MS 2338
Moscow, ID 83844-2338

Phone: 208-885-5883

Fax: 208-885-6654


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