California wineries use owls instead of pesticides

Winegrowers must be very careful with their soil, rain, heat and sun. But rodents like ground squirrels and mice can wreak havoc in a vineyard. Rather than turning to rodenticides to deter pests, graduate students at Humboldt State University in California are testing a more natural approach using owls.


The experiment is part of a long-term research study under the direction of Professor Matt Johnson of the university’s wildlife department. The current cohort, comprising students Laura Echávez, Samantha Chavez and Jaime Carlino, has sporadically placed around 300 owl nesting boxes in the vineyards of Napa Valley. They document the impact of using owls to deter and control pests rather than rodenticides.

Researchers surveyed 75 Napa Valley wineries, and four-fifths now use owl nesting boxes and notice a difference in rodent control. Barn owls have a four-month nesting season, during which they spend about a third of their time hunting in fields. A barn owl family can eat up to 1,000 rodents during the nesting season or about 3,400 in a single year.

So far, graduate students have found that barn owls in vineyards reduce the number of ground squirrels, but not mice. They are also evaluating the impact of owls on voles, but this is inconclusive at this time.

But the most important part of the study is whether or not the presence of these owls led to a decrease in rodenticide use in Napa Valley. Since January 2021, the California Department of Pesticide Regulation has placed stricter limits on the use of rodenticides, which can kill birds and other animals that eat rodents poisoned by rodenticides. These pesticides cause horrific deaths from internal bleeding in rodents that ingest them.

The researchers say most of the wine growers in their study no longer use rodenticides since adding birdhouses to their properties. But it’s not certain that relying on owls will reduce pesticide use in Napa Valley. A recent study found that among farmers who grow wine grapes in Napa Valley, about 80% use nest boxes and about 21% use rodenticides.

“Whether the use of barn owl cans caused this reduction in rodenticides is of course not proven,” Johnson says Bay Nature. “Nevertheless, this result is encouraging.

Farmers have used owls and other raptors to hunt rodents for centuries, but modern chemical pesticides have taken precedence over natural methods in recent times. In an effort to leave less of a negative impact on the environment, farmers around the world are relying on raptors for pest control, rather than toxic pesticides. Birdhouses are appearing in agricultural fields in the United States, Malaysia, Kenya, and Israel to help naturally eliminate rodents that destroy crops.

In Napa Valley, birdhouses aren’t the only tactic for creating more sustainable farmland. Winegrowers also try to minimize water consumption and plowing. They also plant perennial grasses between rows of grapes, as this can reduce soil erosion and improve nutrient and carbon cycling.

Yet there is still a long way to go to improve sustainable agriculture, including in the wine industry. Napa Valley has over 40,000 acres of vineyards and only 3,800 acres are certified organic. With the increasing use of nest boxes, it is hoped that farmers will rely on these more natural methods rather than rodenticides.


Barn Owl: Secret Saviors of Napa Valley Wineries

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