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.
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.
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