Birds can be a mixed blessing for farmers. Sometimes birds increase yields by gobbling crop-eating insects and rodents. But they may also devour crops, ingest beneficial bugs, or harbor pathogens that pose a risk to human health when they show up in food. “We really have to think of [birds] as a package deal, with all of the different ways that each species interacts with the farm,” says Elissa Olimpi, a conservation biologist at Virginia Tech.
For two years, Olimpi spent her spring and summer mornings on strawberry farms, weighing that balance. The work—which involved carefully extracting birds from mist nets and placing them in cotton bags until they could be measured—was also a package deal. “It is really a special feeling to be up before sunrise, hearing birds and having a bird in your hand,” says Olimpi, who was at the University of California, Davis, at the time. But she also had to scoop up poop that birds left behind in the bags and freeze it for later examination. “Sometimes, it can be messy.”
While hosting flocks in their fields has pros and cons for growers, Olimpi’s research suggests there are ways to tip the scales in their favor. In a recent study, published in the Journal of Applied Ecology, Olimpi and colleagues report that the amount of natural habitat around a farm—such as woodlands, shrublands, and wetlands—was the most important factor in determining whether birds offered more benefits than costs. Birds did less crop damage and carried fewer risky pathogens on farms with more wildness.
For farmers, the study offers an endorsement for creating or maintaining natural areas—or, if that’s not an option, installing nest boxes to attract Barn Swallows and other insect-eating birds.
The researchers visited 21 organic farms in California’s Central Coast, which produces nearly half of the nation’s strawberries. Some of the farms featured natural habitats while others included only planted fields. In 2018 and 2019, between March and July, they collected more than 1,000 fecal samples from 55 bird species. Then, like detectives, they inspected DNA traces in the samples to find out what the birds ate and which foodborne pathogens they carried.
On farms without natural areas, the results showed, birds ate up to twice as many strawberries, causing significant crop damage. However, on habitat-rich farms, they opted for more nutritious food sources, like wild seeds, fruits, and insects.
Strawberry farms with natural habitats were also more likely to host bird species that the study ranked as most beneficial for growers, including Barn Swallow, Black Phoebe, California Quail, and Purple Finch. On the other hand, farms without those wild features were more likely to attract species that form large flocks that damage crops, such as European Starling, Bushtit, and American Goldfinch.
The findings may also alleviate farmers’ concerns about food safety risks from birds. In recent years, commercial produce buyers have pressured growers to remove natural habitats to keep away birds and other wildlife suspected of causing foodborne illness, even when livestock proved to be the source of contamination. But the new study and other recent findings suggest that doing so could have the opposite effect. Olimpi’s team found fewer birds carrying Campylobacter bacteria, for example, on farms with wild areas. Irrespective of farm type, her study found Campylobacter in less than 4 percent of all birds, around 2 percent with E. coli, and none with Salmonella. “Even though we are explicitly looking for these pathogens in birds, the risks that we’re seeing are just incredibly low,” Olimpi says.
The study is the first to assess what sorts of agricultural landscapes maximize the benefits birds provide. “There’s been a lot of work on individual ecosystem services, but nobody I think previously had put it all together like this one has,” says Matthew Johnson, a Humboldt State University habitat ecologist who has conducted similar research but was not part of the study.
For more than a century, scientists have recognized the benefits birds provide to farmlands. In 1885, the U.S. Department of Agriculture created an Office of Economic Ornithology to understand which birds could help control pests and which ones might be pests themselves. But this interest in birds as a form of pest control petered out as pesticides became widespread. “There have certainly been major ebbs and flows in our interest in the role of wild birds on farms,” says Sara Kross, a Columbia University environmental biologist.
Over the past two decades, scientific evidence has stacked up on the benefits birds provide to farmers. Johnson’s research, for example, showed that shade trees in Jamaican coffee farms host insects and flowers that attract songbirds like American Redstarts, which also eat pest insects in the plantations. Kross’s work revealed that lining sunflower farms with trees attracted nearly twice as many bird species and reduced pest damage to sunflower seeds by nearly four times. In California’s vineyards, more than twice as many vine-damaging beet armyworms fell prey to birds in farms where researchers set up nest boxes to attract insect-eating Western Bluebirds.
More farmers are now warming up to this idea, Kross says. In her informal interactions with growers and through her research, she has found that most organic farmers like having birds around and are willing to invest in attracting them. “They usually know what the birds like,” Kross says. “They’ve grown up listening to them and watching them, and they’re usually very interested in them.”
Even so, it will take more than a love for birds to convince many growers to spend time and money attracting avian helpers to their land. “Farmers typically are really busy, and to get interested, they want to see some kind of benefit,” says Jo Ann Baumgartner, executive director of Wild Farm Alliance, an organization that works with farmers to set up nest boxes, plant hedgerows and restore riparian habitats to help them reap the economic benefits that birds provide.
Fortunately, the new study adds to a growing body of evidence that farming with nature can be good for birds and for the bottom line. “The farmer can be farming their land in a way that is not only producing food the rest of us enjoy but also harbors biodiversity,” Johnson says. “There’s really an opportunity for a reciprocal relationship right now.”