California vineyards replace toxic chemicals with nesting owls for pest control

Napa Valley vintners who have relied heavily on rodenticides for their pest control are increasingly turning towards winged predators. Vineyards across California are welcoming birds of prey aka raptors like hawks and barn owls to gobble up rats, voles, gophers, etc instead of using rodenticides, all in order to keep their land as toxin-free as possible. Matthew Johnson, professor in the Department of Wildlife at Humboldt State University in northern California, and some of his students have spent the past few years studying the role of birds in these winegrape vineyards and their findings have been extremely encouraging so far.

"Many winegrape farm managers have installed nest boxes for barn owls, bluebirds, and swallows in hopes that the birds control insects and rodent pests such as gophers and voles. My lab is pursuing this line of research with a series of related projects, starting with determining how barn owls select boxes, how they hunt across the landscape, how surrounding habitats affect hunting in the vineyards, and farmers' perceptions of the owls and their potential to control rodents," Johnson explains. Speaking to Living Bird Magazine about his research, he explained that his interest in the topic was piqued as he drove around California wine country.

"I kept seeing these Barn Owl nest boxes in vineyards and thought those have got to be up for more than just feeling good. The farmers have put those up in hopes of trying to control rodents," he explained. "But there hadn't really been a lot in terms of scientific research on the topic." Through their study — which began in 2015 — they found that each chick in a brood consumes nearly 200 pests — gophers, voles, and mice — in the 10 weeks before it fledges from the nest box. "We estimated 3,000 rodents killed over the course of the year by a single family of Barn Owls," Johnson revealed.

The study also found that the owls showed a strong preference for nesting boxes located near nat­ural cover, such as grasslands and oak savanna. Based on this observation, the researchers set out to determine whether the owls nesting in the vineyards prefer hunting amid the grapevines or eating rodents in the nearby wild areas. By tagging some of the owls with GPS tracking devices, they found that even with native habitat nearby, the owls spent a third of their time hunting in cultivated land.

Based on his findings, Johnson advises vineyard owners to leave some wild habitat near the areas where owl boxes are posted. Doing so, he said, creates "an incentive for the farmers to conserve those uncultivated habitats—the riparian areas, the oak woodlands, and so on [that have] strong conserva­tion benefits for all sorts of species, not just the Barn Owls." This partnership could contribute to reducing the environmental footprint of the $9.4 billion industry that has made Napa Valley an internationally known wine region. "I'm interested in two sides of the same coin. How can farms be good for wildlife? And on the flip side, how can some of those birds or wildlife be good for the farmers?" said Johnson.

While ecologists usually use the term "eco­system services" to describe nature's benefits to humans, Johnson prefers a different term. "I think a better way to describe it is more like a gift economy," he said. "This is something we've learned from indigenous cultures. That is, if people do things for wildlife, wildlife will do things for people."