Microplastic loading in terrestrial birds from nonlethal sampling

The accumulation of microplastics (MP, <5 mm), is a global issue that is increasing for a widening list of taxonomic groups and trophic levels. There is little research on MP loading in terrestrial birds, even though their diverse behavior and morphology and their relative ease to study make them useful indicators of the ecological effects of pollution. We tested whether MP were present in terrestrial birds ranging in size from 7 to 36 cm via two methods of nonlethal sample collection: (1) gastrointestinal (GI) tract dissections using 75 already deceased specimens and (2) noninvasive fecal sampling (n = 322) from non-targeted bird capture from July to October 2022 in the USA. We assessed the associations between MP load and aspects of avian ecology. We detected MP with both methods—fecal sampling yielded lower recovery, but results were comparable to GI tract sampling. We demonstrate the value of avian capture and release via bird banding with fecal sampling as a nonlethal approach for larger datasets and the GI tract results suggest long-term retention in the sampled species. Our results suggest that MP loads are more influenced by fine-scale local variation on individuals rather than ecological characteristics like diet or foraging strategy, or morphological variation like body size. We detail the use of fecal sampling during nontargeted terrestrial bird banding to measure MP and the first documentation of MP ingestion for many of the species and locations in this study.