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Project looks at pathogen risks from farmland birds

December 15, 2022
Research led by Daniel Karp, Ph.D., with the University of California, Davis, is picking up where previous projects have left off to examine the prevalence of different wild bird species in agriculture and whether they carry and transmit food-borne pathogens. From there, he hopes to develop a photographic guide to help growers identify birds and the potential food safety risks they may pose under different contexts.

Key Take-Aways

• Little is known about potential risks posed by many bird species frequenting farm fields.
• Project is collecting fecal samples from birds caught in fields and assaying them for 3 pathogens.
• Crews also are sampling bird feces found in fields and determining how long pathogens survive in bird feces.
• Results will be used to develop a holistic food safety risk assessment for farmland birds.
“We’re trying to figure out how we can co-manage these agricultural systems for food production, food safety and bird conservation at the same time,” Karp said. “It’s not like you can exclude all birds from farms. We’re trying to understand the relative risks of different species and how farm management affects those risks.”
Much of the previous research on enteric pathogens in wild birds focused on species that congregate in large flocks around animal feeding operations and refuse sites, such as starlings and gulls, respectively. But Karp said little is known about the risks posed by many other bird species, ranging from bluebirds to swallows to killdeers, frequently found in farm fields or simply flying over them.
“We started work on this years ago, building up a large dataset to get more information about which birds are carrying pathogens and defecating in fields,” he said. As part of continuing work, they have already built a dataset that includes more than 100 bird species and more than 10,000 pathogen tests.
Joining him in the project, titled “Towards a holistic assessment of the food-safety risks imposed by wild birds,” is co-principal investigator Jeffery McGarvey, Ph.D., with the U.S. Department of Agriculture’s Agricultural Research Service.
“My training’s in ecology, so it’s really essential to be working with Jeff, who’s a microbiologist and doing the molecular work,” Karp said.
The current project grew out of conversations Karp had with producers who were unsure of the risks posed by birds. If they implemented a 1-meter or so buffer around each feces they found — even the small ones produced by perching birds — large portions of their fields would have to be disked.
Karp and his crew are working with 20 California farming operations that gave them access to their fields to survey for feces and capture birds using mist nets. Without this type of cooperation, Karp said the research would not be possible.
“It’s key — those relationships are so important,” he said. Cooperating farms also receive research updates.
Karp was quick to point out that he has the necessary permits and training and years of experience that allows birds to be handled without injury.
One part of the project involves capturing birds, identifying the species and collecting fecal samples to assay for Campylobacter, Salmonella and Shiga toxin-producing E. coli. The birds are banded before being released so they can be quickly identified if recaptured.
Crews also are conducting fecal transects, where they grid out an area, search for feces and sample any they find. So far, Karp said, they’ve collected about 1,000 samples. Using DNA, McGarvey is often able to identify the species from which the feces came and whether pathogens are present.
In the third part of the project, the researchers inoculated about 200 fecal samples from wild turkeys and Western bluebirds with E. coli in experimental field plots. The samples were placed on one of three different substrates — bare soil, plastic mulch or lettuce leaves — to determine how long pathogens survive in bird feces under field conditions.
“Early on, we wanted to know if the bird identity mattered or if survival just depended on the size of feces,” Karp said. Preliminary results found both fecal size and the substrate type affected die-off, with the pathogens dying off faster in the smaller masses than in the larger ones. Bacterial survival also was lower on soil and plastic mulch than on lettuce leaves.
From their results, Karp said he plans to develop a holistic food safety risk assessment for farmland birds.
“There might be instances where it would be a benefit for farmers to have birds in their fields,” Karp said about birds that feed on insects or other pests. “Our early results found that small insect-eating birds produce small feces, and pathogens don’t seem to survive long in these. If we find these species present relatively low risks to food safety, then farmers might be able to take advantage of the small birds that provide them benefits while excluding the species that pose food safety risks.”
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