Bluebirds are not picky about what they eat: caterpillars, beetles, and grasshoppers are all fair game.

NOVEMBER 14, 2011, 7:35 AM

In a California Vineyard, Bluebirds Earn Their Keep

By RACHEL NUWER

Julie JedlickaA male Western bluebird on a vineyard trellis.

In an innovative study, nest boxes installed at a California vineyard attracted hundreds of birds that picked the farmers’ crops clean of pests in exchange for the free housing. The experiment is heartening news for conservationists amid reports of shrinking habitats and population declines for so many species.

“Placing songbird nesting boxes in agricultural landscapes can provide suitable nesting sites for a lot of birds that used to be plentiful 100 or 200 years ago but lost their natural landscapes,” said Julie Jedlicka, an ornithologist at the University of California, Berkeley.

Dr. Jedlicka set out to study whether installing the nest boxes would help attract the birds and reduce pests. Her research, published last week in the journal PLoS One, confirmed her hunch. Compared with control areas in the same vineyard that did not have the nest boxes, areas with the boxes attracted twice as many birds early in the nesting season and had 2.6 times as many birds later in the breeding season.

Western bluebirds were responsible for much of the increase: 313 of them were counted at the nest box sites, versus 39 in control portions of the vineyard.

Over all, 1,122 birds representing 25 species made an appearance. Both the nest box sites and the sites without boxes had about the same number of species present, but the numbers of insect-eating species was 50 percent greater in areas with the nest boxes. Insectivorous birds removed about 2.4 times as many insect larvae at the nest box sites as they did in the control
areas.

                                                  
     Laura BarrowJulie Jedlicka checks on a nest box in a vineyard in central California.

Dr. Jedlicka’s idea is not new. From 1885 to 1940, the federal
Department of Agriculture devoted resources to studying “economic ornithology,” or using birds as biological controls for agricultural pests. After pesticides like DDT were developed during World War II, that approach largely faded in favor of a quick chemical fix. Now Dr. Jedlicka envisions a revival of economic ornithology through the lens of ecosystem services and bird conservation.

As cavity-nesting songbirds, bluebirds are particularly well suited to the task. Although they look for enclosures to build their nests, they tend to prefer those found within otherwise open spaces, and agricultural fields fit the bill. What is more, “they respond rapidly to new nesting opportunities,” Dr. Jedlicka said. Within one year of placing about 100 nest boxes in two vineyard study sites, bluebird families occupied over 75 percent of the boxes, she said.

Bluebirds are not picky about what they eat: caterpillars, beetles, and grasshoppers are all fair game. A bluebird family of five nestlings requires 125 grams of arthropods per day, and bluebird pairs can produce two broods per year.

The birds probably won’t replace farm pesticide use entirely. Some pests, like spider mites, are too small for bluebirds to consume.

Dr. Jedlicka hopes that wineries will gradually adopt the “Bird Friendly®” stamp, a certification already widely available for coffee growers. Vintners could then market their products to the growing eco-friendly consumer sector while helping the birds.

Wine growers aren’t the only farmers who can benefit: the combined range of North America’s three bluebird species extends across the United States. Farmers in Florida already use nest boxes to attract insect-eating birds, as do some apple orchard managers in New England.

Nest boxes can be used to attract bluebirds to urban gardens as well. “I imagine it would be difficult to find an agricultural system where this wouldn’t work,” Dr. Jedlicka said.