Towards a holistic assessment of the food-safety risks imposed by wild birds

Towards a holistic assessment of the food-safety risks imposed by wild birds

Jan. 1, 2022 - Dec. 31, 2023

$370,123.00

Daniel Karp, Ph.D.
University of California, Davis

Jeffery McGarvey, Ph.D.

Poster

Poster

Birds introduce complex food-safety risks, as they carry multiple pathogens, are difficult to exclude from farms, and regularly defecate on crops. Yet very few wild bird species have been studied, and those that have form a minority of farm bird communities. Moreover, existing studies stop at examining pathogen prevalence in birds and do not holistically assess foodsafety risk. For a species to pose a significant risk, it must carry pathogens, visit fields, defecate on crops, and produce feces that support pathogen survival. Here, we propose to first identify species that carry pathogenic E. coli, Salmonella, and Campylobacter by coupling existing studies with assays of field-collected feces. Second, we will survey birds and collect feces on 15-20 farms near rangeland, natural habitats, or produce farms to determine which species enter farms and defecate on crops and in which contexts. Third, we will compare E. coli survival between feces placed on different substrates (crops, organic/conventional soils, plastic mulch) and between feces from different species. Finally, we will compile holistic risk assessments for >50 species into a photographic guide to help growers identify and manage birds. Ultimately, we hope to help growers implement practices that bolster beneficial species without compromising food safety.

Technical Abstract

Foodborne disease outbreaks attributed to wildlife have heightened pressure on growers to prevent wildlife from entering their farms (Beretti and Stuart 2007, Gardner et al. 2011, Langholz and Jay-Russell 2013, Baur et al. 2016). Birds are of particular concern as they carry enteric pathogens and move long distances, including between livestock operations and fresh produce fields (Rivadeneira et al. 2016, Navarro-Gonzalez et al. 2019, Smith et al. 2020b). As a result, growers often implement economically and ecologically costly measures to prevent bird intrusion (e.g., bird netting and habitat removal; Beretti and Stuart 2007, Karp et al. 2015, Olimpi et al. 2019). However, despite widespread concern, our knowledge of the risks posed by different species by farming context is still in its infancy. Few species have been studied, with disproportionate focus on species that frequent feedlots, refuse sites, or water bodies rather than crop fields (Smith et al. 2020b). Moreover, no studies have assessed the entire pathogen spillover cycle; that is, the combined likelihood that bird species carry pathogens, enter farms, defecate on crops, and produce feces that enable pathogen survival (Smith et al. 2020b).

We will produce holistic food-safety risk assessments for wild birds on produce farms in California. We have already assembled a database of ~10,000 pathogen tests across ~100 bird species (i.e., Campylobacter spp., Shiga-toxin producing E. coli, and Salmonella spp. assays). First, we will capture wild birds on or near farms, collect their feces, and test them for each pathogen, prioritizing birds that are poorly represented in our database, especially those that use nest boxes. Second, we will quantify how proximity to rangeland affects bird abundance on farms and identify species most likely to defecate on crops. Specifically, across 15-20 farms, we will census birds, collect feces, and use DNA barcoding to identify which species produced ~1,000 fecal samples. Third, we will conduct laboratory and field experiments to estimate E. coli survival curves in feces from different bird species, placed on lettuce, organic/conventional soils, or plastic. Finally, we will combine our data on pathogen prevalence, defecation rates, and pathogen survival to develop risk assessments for common farmland bird species.

Assessing which species increase near rangeland will allow us to contextualize our findings and help farmers develop farm-specific management strategies. For example, based on preliminary data, we suspect birds associated with livestock will be more likely to carry pathogens, intrude into farms, and defecate on crops. If true, then growers near rangeland would be advised to deter birds, whereas those further away may be able to co-manage their farms for food safety and bird conservation. Indeed, farmers regularly use nest boxes to attract insect-eating birds to their farms and control crop pests (Jedlicka et al. 2011): we will assess the food-safety risks associated with these species. Upon completion, we will disseminate our risk assessments and management strategies through webinars and a photographic guide that will help growers identify birds on their farms and assess their risks.