California vineyards are shifting from using toxic chemicals to nesting owls for pest control

Winemakers need to pay close attention not only to their soil but also to the heat, rain and sunlight. Even a well-maintained vineyard can be ravaged by pests like mice and gophers.

Napa Valley vintners used rodenticides to control pests for a long time. But, Humboldt State University graduate students in California are exploring owls as an alternative.

The experiment is spearheaded by professor Matt Johnson of the university’s Department of Wildlife. The researchers randomly placed around 300 owl nest boxes through Napa Valley vineyards to document the birds’ impact on deterring and removing pests.


The students surveyed 75 wineries in the region and found that four-fifths use the owl nest boxes. They also noticed a decrease in rodents.

Barn owls spend a four-month nesting period, and one-third of their time hunting in the field. A family of barn-owls can eat up to a thousand rodents each year during their nesting season.

Graduate students have so far discovered that barn owls in vineyards decrease the population of gophers but not mice. They are also assessing the owls’ impact on voles, but that remains unclear at this time.

A barn owl

The most important aspect is whether the presence of barn-owls has resulted or not in a decrease of rodenticide usage in Napa Valley vineyards. The California Department of Pesticide Regulation has set stricter limits on rodenticide use as of January 20, 2021.

These pesticides can cause internal bleeding and eventually death in rodents who ingest them. The rodenticides can also cause death of birds and other animals that eat rodenticides.

Researchers found that the majority of vintners who participated in the study have stopped using rodenticides after installing nest boxes on their property.

“Whether the use of barn owl boxes caused that reduction in rodenticides is, of course, not proven,” Johnson told Bay Nature. “Nonetheless, this result is encouraging.”

Johnson and the graduate students learned from Johnson that barn owls prefer their boxes to be at least nine feet above the ground, facing away towards the sun, adjacent grassy fields, far from forested areas.

A pair of barn owls

Farmers have relied on owls for centuries to hunt rodents. Modern chemical pesticides have overtaken natural methods in recent years.

Farmers worldwide are returning to raptors as a way to reduce their environmental impact.

The good news? Nest boxes are appearing in other countries for other crops, including Kenya (mixed vegetable), Malaysia (palm Orchards), Israel (alfalfa) and Israel (alfalfa), which help farmers remove rodents from crops.

Bay Nature was informed by John C. Robinson (an ornithologist from the Bay Area).

“You can literally put a barn owl nest box in the exact location where you think you have a problem with the small mammals, and voilà! The owls will start using that area.”

An owl nest box

Napa Valley wine grape farmers are encouraging a more sustainable farmland. This includes putting up nest boxes, minimizing water usage, and not tilling as much. Perennial grasses are being planted by farmers between rows of grapes to reduce soil erosion, improve nutrient andcarbon cycling, and increase yield.

Napa Valley boasts more than 4,000 acres worth of vineyards. 3,800 acres are organic.

Despite these advancements, there is still much to be done to ensure sustainable agriculture in all areas, including the wine industry. Nest boxes are becoming more popular and farmers around the world will be able to use them instead of toxic rodenticides.

Click on the video below to learn more about Napa Valley’s barn owls.

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