Differences in microplastics in passerine feces across species, diet, and foraging location

Environmental microplastics (MPs) are ubiquitous contaminants with potential to harm organisms, including birds. Birds are exposed to MPs, although the mechanisms through which they ingest MPs are currently unclear. Examining the gut contents or feces of birds has provided insight into their ingestion of MPs, but previous research has put relatively little focus on passerines, which are the largest and most diverse order of birds. We collected fecal samples from five species of passerines which vary in their diets and foraging locations: Common Yellowthroat Geothlypis trichas, Gray Catbird Dumetella carolinensis, Northern Cardinal Cardinalis cardinalis, Wood Thrush Hylochichla mustelina, and White-throated Sparrow Zonotrichia albicollis. We quantified and characterized MPs in fecal samples, and used procedural and field blanks to account for MP contamination. We found MPs in samples from all five species. Ground foraging birds had more MPs in their feces by both count and density. While all species had mostly fiber-shaped MPs in their feces, insectivorous birds had more fragment-shaped MPs compared to birds with mixed diets. Transparent was the most common color of MP across all species. Our results suggest that MP exposure differs between species based on characteristics of their feeding behavior, and thus certain species of passerines may be more at risk than others of the deleterious effects of MPs on fitness. Moving forward, bird feces could be used to monitor MP presence in the environment, but it is important to consider these differences among species when designing monitoring efforts.