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Birds and Berries – Friend or Foe?

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By Lucas Patzek, Napa County Resource Conservation District and Ariel Rivers, NACD Pacific Region Representative

Photo Credit John Comisky

No one can be blamed for thinking that birds and berries don’t mix. Anyone growing grapes or blueberries has at some point broken into a sweat or paced their fence line with a pitchfork after spotting a cloud of starlings on the horizon. But not every bird is bent on eating the fruit, and in fact, native birds can provide many on-farm benefits.

In California’s wine country, Wild Farm Alliance recently partnered with the Napa County Recourse Conservation District (Napa RCD) and others to hold an “All Things Avian” field day about supporting beneficial birds and managing pest birds in the vineyard. It was a unique gathering of farmers and ornithologists to explore the latest research, learn about farmer assistance programs, and view birds up close using mist-nets.

Photo Credit John Comisky

Songbirds, especially insectivorous and cavity nesting types (those that build nests in sheltered chambers), can reduce pest damage, reduce yield loss, and help maintain fruit quality. Dr. Julie Jedlicka of Missouri Western State University presented some of her research findings concerning bluebirds and pest control in California’s vineyards. A diet analysis of adult and nestling Western Bluebirds revealed they predominantly eat herbivorous insects. Thus, the birds are selectively eating insects that are likely to be feeding on the crop or transmitting plant-infecting diseases. For instance, sage leafhopper was found in 55 percent of all birds sampled. This finding suggests that bluebirds can control major grape pests, including leafhoppers and sharpshooters, some of which are insect vectors for the dreaded Pierce’s disease. Dr. Jedlicka also found bluebirds ate hardly any beneficial insects, so natural predators of the pest insects were left to do their work in the vineyard.

Birds of prey can reduce the presence of pest birds and rodents on the farm. Dr. Sara Kross of Columbia University and Dr. Matt Johnson of Humboldt State University discussed the benefits of barn owls and falcons. Dr. Kross showed that introducing falcons into vineyards resulted in a dramatic reduction in pest birds, including 83 percent fewer blackbirds and 79 percent fewer starlings. With fewer pest birds, there were 95 percent fewer removed grapes and 55 percent fewer pecked grapes in the study areas. The presence of a falcon could potentially result in savings of $234/ha for Sauvignon Blanc and $326/ha for Pinot Noir. Dr. Johnson’s lab has been studying barn owls on 65 Napa Valley vineyards and has found they are killing large numbers of rodents that could otherwise cause damage to soil, the vines, and eat fruit depending on the critter. In fact, one owl box containing two adults and four nestlings can kill over 1,000 rodents in an average breeding season. Preliminary GPS tracking information shows barn owls residing in on-farm nest boxes hunt about one-third of the time within the vineyard. Thus, the average owl box can remove 333 rodents from a farm based on their standard hunting ranges. Barn owls also have no problem nesting close to each other, so several owl boxes can be installed in each vineyard.

Conservation districts and the Natural Resources Conservation Service (NRCS) play an important role in bringing the science of predatory birds to the field by promoting the adoption of agricultural practices that support birds and increase on-farm resilience. As one example of augmenting predatory bird habitat, the Napa RCD launched the “Re-oaking the Valley” project with the goal of planting hundreds of native trees and shrubs each year on farms and public lands with the help of school kids and community volunteers. California’s oak woodlands sustain higher levels of biodiversity than virtually any other terrestrial ecosystem in the state, and over 150 bird species depend on them. Thus, the Napa RCD has prioritized tree-planting and woodland restoration to address oak losses resulting from development and wildfire, and farmers have been key partners in this effort. In 2018, Napa RCD planted 1,315 native plants, including 346 oak trees, throughout the district with the community’s help.

Napa RCD and NRCS technical staff also provide free technical assistance, and sometimes financial assistance, to farmers interested in implementing bird-friendly farming practices, including hedgerow plantings and raptor perches. These practices can provide opportunities that are mutually beneficial for farmers and wildlife by enhancing habitat within vineyards, while reducing pest control costs and increasing the quantity and quality of yields.

Photo Credit John Comisky

A perfect example is installing nest boxes to attract insectivorous songbirds like bluebirds, tree swallows and house wrens. Nest boxes can also be used to attract barn owls and kestrels to the farm. The style of nest box should be chosen based on local bird species, climate, predators and other factors, and construction plans are available from NRCS and the Cornell Lab of Ornithology.

Artificial perches that are 10-15 feet tall with a single crossbeam will also increase the hunting activity of raptors on the farm. Lastly, providing even a small amount of habitat around the farm can significantly increase the diversity and abundance of beneficial birds. Riparian areas and large trees will provide habitat for songbirds, and many raptors hunt from trees, use them for resting, and nest in them. Farmers can plant hedgerows if there are no trees on or adjacent to their land. Napa RCD’s and NRCS’ conservation planners are also aptly prepared to assist local farmers in the selection of appropriate species to include in hedgerows and appropriate management practices to best attract beneficial species.

Next time you pour a glass of Napa Cabernet, remember that bluebirds and barn owls are one of the secrets to world-class wines!

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