COS 24-4 - Moving towards a holistic assessment of the food-safety risks imposed by wild birds

Abstract: Wild birds pose a unique food-safety risk to agriculture as they carry multiple zoonotic pathogens, are difficult to exclude, and most are federally protected. As a result, farmers have few strategies for reducing bird fecal contamination on their crops. While foodborne pathogen prevalence in avian fecal samples has been studied in some species of wild birds, research often stops at this stage, preventing a holistic evaluation of the food-safety risks imposed by avian communities. Here, we evaluate the food-safety risks of wild birds, from the point of entering farms through harvest of the crop via three complementary approaches. First, we investigated which species are more likely to shed Salmonella, Shiga toxin-producing E. coli, and Campylobacter. Specifically, we expanded a previous database of >11,000 samples across 94 species by collecting fecal samples from 16 under-sampled bird species and assaying them for each pathogen. Second, for crop contamination to occur, infected birds must be present on or over agricultural fields and defecate on the crops. We conducted bird surveys and collected fecal samples for species identification on over 20 leafy-green farms across the Central Coast of California during the planting and harvest seasons. Finally, for successful transmission to occur, pathogens must survive in fecal samples until harvest. We conducted laboratory and field experiments examining E. coli survival in feces from diverse set of bird species, which were then placed on lettuce, soil, and plastic mulch. Our results suggest food-safety risks from birds are dynamic and change across the growing season. Twice as many individuals and nearly quadruple the number of bird flocks were observed in the fall harvest season compared to spring and summer. Despite changes in avian abundance, the community of species remained relatively similar across harvest seasons. Importantly, not all species carried the same risk in terms of pathogen survival. We found that fecal mass was the strongest predictor for how long E. coli survives, with increased survival in larger fecal samples, especially on lettuce plants. Larger birds— with larger feces— may thus carry greater food-safety risks. By investigating which birds are more likely to harbor pathogens, which birds occupy agricultural habitat, and how long pathogens survive in feces after bird defecation, our work contributes to a more holistic understanding of the risk wild birds pose to food safety. These results will better inform farmers and policy makers on how to co-manage agricultural lands for both conservation and human health.