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

There are many things that winemakers must pay close attention to, including their soil, the heat, the rain, and the sunlight. However, pests like gophers and mice can wreak havoc even on a well-maintained vineyard.

Napa Valley vintners have long relied on rodenticides to eradicate pests, but graduate students at Humboldt State University in California are studying the use of a safer alternative: owls.

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.

An owl nest box in a vineyard
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The students have surveyed 75 wineries in the area, and four-fifths now use the owl nest boxes and notice a change in the presence of rodents.

Barn owls have a four-month nesting season, one-third of which they spend hunting in the fields. A family of barn owls may eat as many as a thousand rodents during the nesting season, which equates to around 3,400 in a year.

So far, the graduate students have discovered that the barn owls in vineyards are reducing the gopher population, but not mice. They are also assessing the owls’ impact on voles, but that remains unclear at this time.

A barn owl
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The most important aspect of the study is whether or not the presence of barn owls has resulted in a decrease in rodenticide use in Napa Valley vineyards. As of January 2021, the California Department of Pesticide Regulation imposed stricter limits on the use of rodenticides.

These pesticides cause internal bleeding and ultimately death for the rodents that ingest them. The birds and other animals that eat rodents poisoned by the rodenticides can also die.

According to the researchers, most of the vintners in their study have stopped using rodenticides ever since installing nest boxes in their properties.

“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 have learned that barn owls like their boxes to sit at least nine feet off the ground, facing away from the sun, adjacent to grassy fields, and far from forested acres.

A pair of barn owls
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For centuries, farmers relied on owls and other raptors to hunt rodents. However, modern chemical pesticides have outweighed natural methods in recent times.

In an effort to lessen their environmental impact, farmers worldwide are going back to using raptors to control pests rather than toxic pesticides.

The good news is that nest boxes are popping up in agricultural fields for other crops across other countries, including Kenya (mixed vegetables), Malaysia (palm orchards), and Israel (alfalfa and other crops), helping farmers naturally remove rodents that ruin crops.

John C. Robinson, a Bay Area-based ornithologist, told Bay Nature:

“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
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In Napa Valley, wine grape growers are promoting a more sustainable farmland by putting up nest boxes and minimizing their water usage and tilling. The farmers are also planting perennial grasses between rows of grapes to help reduce soil erosion and enhance nutrient and carbon cycling.

Napa Valley has more than 4,000 acres of vineyards, and 3,800 of those acres are certified organic.

Despite these improvements, the world still has a long way to go to develop sustainable agriculture, including in the wine industry. But with the rising popularity of nest boxes, there is hope that farmers all over will use these natural methods over toxic rodenticides.

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

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