“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.”
