A one-ounce, stocky blur of blue that warbles a melodious song, rarely strays far from its breeding area, enjoys foraging from a perch, and loves to sleep in a nest of twigs in pre-existing cavities may not seem like an excellent candidate for the annihilation of one’s foes.
Which helps explain why western bluebirds, and many of their twee counterparts, have “flown” under the radar for so long.
“People are still surprisingly ignorant about the bluebird phenomenon,” says Tom Clark, who is based in Napa, owns and manages vineyards and works as a consultant for growers hoping to lure bluebirds and swallows into the vines. “There’s a growing awareness in Napa and Sonoma through word of mouth, and the number of wineries and growers I’ve built and installed boxes for in the past three years has gone up exponentially.”
As winegrowers slowly but surely see the positive impact of these birds on the health of their vineyards and the quality of their wines, Clark says the price of entry (about US$65 per custom-built box, $110 for a site visit) is getting worked into annual farming budgets.
How many insects can these birds consume?
It’s hard to track just how many pests bluebirds and other songbirds manage to eat because they are constantly on the move, and their prey is minuscule. But Dr. Julie Jedlicka, associate professor of biology at Missouri Western State University, managed to analyse DNA fragments of the birds’ faeces in a survey in California’s vineyards.
The analysis, published in The Auk: Ornithological Advances, found that bluebirds ate primarily herbivorous insects, including chronic vineyard pests.
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Breanna Martinico, PhD, a human-wildlife interactions advisor at the University of California, Davis, is in the midst of a DNA-based survey in Napa with other scholars considering which birds target pests in vineyards and what type of habitats they prefer.
“From our initial findings, conducted over two years, we’re finding that bluebirds and tree swallows are attracted to viticultural habitats with nest boxes,” Martinico says. “They like to forage for insects about 200 meters from the box, or closer. Our data shows that bluebirds and tree swallows are consuming alfalfa hoppers, vine mealybugs and blue-green sharpshooters. Bluebirds are also eating variegated and Virginia creeper leafhoppers. These are all vineyard pests!”
The implications, Martinico maintains, are vast.
“If we can reduce the use of chemicals by creating habitats for birds, it’s good for everyone,” Martinico says. “A lot of songbird populations are down because of overdevelopment and invasive species. This helps them, and it helps vineyard owners. It’s also much better for the environment. Imagine if we implemented these practices everywhere?”
A natural solution to chemical dependency
The implications have also arrested the attention of Ivo Jeramaz, winemaker and vice president of vineyards and production at Grgich Hills Estate in Napa. The winery became certified organic in 2006, then Regenerative Organic Certified in 2023. While reducing inputs and boosting biodiversity in the vineyard is part of Jeramaz’s vision for the estate vineyards, he admits that the transition has required adjustment.
“Biodiversity can be a double-edged sword,” Jeramaz says. “Because we steward our land without chemical pesticides and encourage a diverse host of plants and animals to call our vineyards home, creatures of the pestilent variety can take up residence where we prefer them not to.”
To prevent vine mealybugs, leaf hoppers and sharpshooters from “devouring” the vines, he says they’ve installed hundreds of bird boxes designed to lure bluebirds and tree swallows into their vines.
“Our vineyards are an ecosystem, where every creature has a niche to fill,” he says. “While this means that we will never fully eradicate pest species the way a heavy dose of pesticides might, it does mean that we build resilience, ensuring our vineyards can adapt to new environmental stressors more effectively.”
Designing vineyards as ecosystems
At Two Mountain Winery in Washington’s Yakima Valley, vineyard operations manager Patrick Rawn says that he approaches their 430-acre estate as an entire ecosystem, instead of a vineyard.
While they don’t have nest-boxes, and bluebirds aren’t regularly spotted in the region, Rawn says the vineyard team is “developing and reclaiming unfarmable spaces on our farm to promote a natural habitat for the songbirds as part of the ecosystem.”
Since replanting these areas with native plants and shrubs, which are attracting goldfinches, warblers, wrens and magpies.
“We are still in the early stages of directly measuring the impact on bugs,” Rawn says. “But we are starting to see macro-level reduced pest pressure since undertaking the project two years ago.”
