Some birds are viewed as pests and vectors of foodborne pathogens in farmlands, yet birds also benefit growers by consuming pests. While many growers seek to exclude birds from their farms, few studies ask how the functional role of birds shifts across farming contexts. We ask how local (i.e., hedgerows, multiple crops) and landscape (e.g., more non-crop habitat surrounding farms within 1.5km) level diversification influence the likelihood of different bird species to function as beneficial, pest, and vector species. We captured birds and collected fecal samples, and surveyed crop fields for fecal contamination, on 20 California strawberry farms that varied in local management practices and landscape context. We characterized bird diets using a combination of metabarcoding and targeted PCR to screen for a key pest (Lygus hespersus), strawberries, arthropod natural enemies (e.g., spiders, ground beetles etc.), and foodborne pathogens (pathogenic Escherichia coli, Salmonella, and Campylobacter) in bird feces. We tested the effect of local and landscape diversification in determining the probability that different bird species consumed pests, potentially disrupted pest suppression by consuming arthropod natural enemies, damaged crops, and vectored foodborne pathogens.
Results/Conclusions
We captured 1,498 birds, representing 74 species, and collected 1,328 fecal samples. We found very low incidence rates of E. coli and Campylobacter (<4%), and did not detect Salmonella in any samples. E. coli incidence was weakly negatively correlated with seminatural habitat, such that birds were less likely to carry E. coli on farms with more conserved habitat in the surrounding landscape. Campylobacter incidence was significantly lower on farms surrounded by more seminatural habitat. We also found that fecal contamination in crop fields did not increase with seminatural habitat. From preliminary analyses, we also found that birds were most likely to function as pests (i.e., consuming strawberries) on monoculture farms in landscapes with little remaining seminatural habitat. Finally, our preliminary analyses also indicated that the influence of seminatural habitat surrounding farms had differential effects on invertebrate pest and natural enemy consumption for different bird species. In recent years, market pressures have encouraged farmers to remove non-crop vegetation in an effort exclude wildlife from farms and mitigate food safety risks. Our results suggest that habitat removal does not increase pathogen prevalence or fecal contamination, and could exacerbate crop damage. Taken together, our findings suggest that conserving natural habitat in farming landscapes may help to limit the role of birds as both pests and vectors on farms.