Assessing foodborne pathogen survival in bird faeces to co-manage farms for bird conservation, production, and food safety.
Abstract
Because birds can carry foodborne pathogens, widespread concern exists that birds impose food-safety risks to farms. Growers are thus often encouraged to deter birds and forego harvesting crops near bird faeces (e.g., no-harvest buffers). Developing a holistic understanding of the pathogen spillover process-from individual infection to pathogen persistence on crops-is essential to understand and manage food-safety risks associated with birds. Here, we coupled field and greenhouse experiments to understand the relative risks associated with different bird species on California farms. We first compared E. coli survival in bird faeces on lettuce, soil, and plastic mulch to identify where pathogens are likely to persist. Next, we quantified pathogen survival in faeces from 10 bird species to identify higher-risk species. Finally, we combined pathogen survival data with bird surveys and faecal transects to assess food-safety risks across 29 California lettuce farms. E. coli abundance rapidly declined in bird faeces, but rates varied across substrates. E. coli survival was higher on lettuce compared to soil and plastic mulch, likely because of lettuce's cooler and wetter microclimate. E. coli persistence was also much higher in faeces from larger birds-which produce larger faeces-than small songbirds. Importantly, minimal differences in persistence among species were observed after all faeces were standardized to the same mass. Though bird faeces were common on farms, most birds entering farms, contacting crops, and defecating on crops were small songbirds that defecate small faeces. Coupled with our finding that ~90% of faeces were deposited on soil, these results suggest that most birds on farms present relatively low food-safety risks. Synthesis and applications. Growers are often encouraged to deter all bird species and forego harvesting crops near all bird faeces, but our work suggests not all birds and faeces pose the same food-safety risks. If growers ignored small bird faeces on soil, then we estimate that the area of California lettuce farms affected by no-harvest buffers could decrease from ~10.3% to ~2.7%. More broadly, our results suggest farmers could promote small, insect-eating birds by erecting nest boxes or preserving habitat without necessarily compromising food safety.