Farmers cleared habitat to reduce wildlife disease. For birds, their efforts backfired.

A deadly 2006 E. coli The spinach outbreak from a farm in central California prompted growers there to clear pastures and forests that line their fields, amid fears they harbored disease-carrying wild animals. It appears that strategy may have done more harm than good.

Birds on farms in California with wild habitat nearby were less likely to have disease-causing microbes in their feces, while also feeding less on farmers’ crops, scientists have learned. The new findings point to possible benefits of farming alongside nature, and the ways in which strategies aimed at warding off wildlife can have unexpected consequences.

The research suggests “that agricultural landscapes with natural habitat tend to be good for conservation, farmers, and public health,” said Daniel Karp, an ecologist at the University of California, Davis whose laboratory led the work.

The 2006 incident sickened at least 204 people in 26 states and Canada, including 104 who were hospitalized. Three people died. For some time, the US Food and Drug Administration recommended against eating fresh spinach. Clues eventually led federal inspectors to a 2.8-acre field in San Benito County, a farm-dotted region just south of California’s Silicon Valley. That’s where they found the tribe E. coli in faeces of neighboring cattle and wild pigs, as well as river water.

The consequences extended far beyond the lone farm, shaking the fresh produce industry, especially in California. Among the new food safety measures adopted in the wake of the outbreak, farmers were pressured to fence fields and remove strips of nearby wild vegetation to reduce the presence of wild animals that carry disease. can carry

But Karp and his fellow scientists questioned whether such measures really had the intended effect. To find out, they focused on one type of organism known to carry disease-causing bacteria — wild birds. Farmers often have a conflicted relationship with birds. On the one hand, they feed on nasty crop-eating insects. On the other hand, they can feed on the same crops as beneficial insects.

To tease apart the interplay of these different forces, researchers went to 21 organic strawberry farms in Santa Cruz and Monterey counties armed with delicate nets known as mistnets. Between 2017 and 2019, the scientists caught more than 1,000 birds of 55 species and collected faecal samples. In the lab, they sifted through the DNA in the feces, looking for clues about what insects and plants they ate, and what germs they carried.

At the same time, the researchers built maps of the farms and the surrounding land, tracing the mosaic of crops and untended vegetation that they described as “semi-natural habitat.”

The results showed that what went into a bird depended in part on the landscape in which they were caught. Birds caught on a dozen farms classified as having relatively little surrounding natural habitat were more likely to have strawberry DNA in their feces, as well Campylobactera bacterium which can cause diarrhea and vomiting in humans, and, in rare cases, death, according to findings reported February 22 in the Journal of Applied Ecology.

The presence of natural habitat stood out statistically as the most important factor when it came to whether the benefits of wild birds outweighed the harm, according to the researchers. “Bird communities respond to changes in the landscape,” said lead author Elissa Olimpi, who was a postdoctoral scientist at UC Davis during the study. “As birds change in response to management, so do the costs and benefits they provide.”

Although it is not exactly clear why closer to natural habitat might be a plus, it is possible that these areas provide more attractive food such as seeds and insects, leading birds to ignore strawberries. The more heavily farmed areas may also support bird communities that are more likely to carry or transmit disease.

Among the various species, barn swallows received a “gold star”, partly due to their appetite for plague. The aerial acrobats catch insects on the wing and build mud nests in the underside of roof trees. The American goldfin, meanwhile, was at the other end of the spectrum.

The split between species suggests that farmers can take steps to encourage more beneficial birds. In addition to letting the land grow wild, people could leave barn swallow nests untouched and build bird boxes with entrance holes small enough to let insect-eating birds in to build nests while excluding larger, more harmful birds like starlings, the scientists said. “The best thing we can do is to understand how we can take advantage of the benefits while reducing the harm,” said Olimpi. “Growers will tell you it’s impossible to keep birds off your farm.”

Olympia, op. already “Semi-natural habitat surrounding farms promotes multifunctionality in avian ecosystem services.” Journal of Applied Ecology. February 22, 2022.

photo taken by Katherine Kerlin, “Birds, Strawberries, and Natural Habitat Study,” University of California, Davis


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