Ecological interactions influencing microplastic loading in small terrestrial birds

The accumulation of microplastics (MP <5mm), is an increasing global problem. MP ingestion causes intestinal blockage, and the chemicals MP readily absorb increase the risk of developmental dysfunction and other health problems. There is little research on MP loading in terrestrial birds despite their usefulness as indicators to measure the ecological effects of pollution using their diverse behavior and morphology, as well as their relative easiness to study. Here, we tested whether MP were present in terrestrial birds ranging in size from 7-36 cm via two methods of collection: (1) gastrointestinal (GI) tract dissections using already-deceased specimens and (2) non-invasive fecal sampling via non-targeted bird capture. We assessed the impacts of ecology on MP loading among species using published behavioral and morphological characteristics. We found MP using both collection methods. Most were identified by Fourier Transform Infrared (FTIR) spectroscopy as polyethylene, rayon, polyester, or nylon. MP were ubiquitous across species, banding locations, body size and ecomorphotypes. Nesting behavior predicted MP loading in both GI tract and fecal data. Cavity nesters were more likely to have higher MP loads, possibly attributed to a higher chance of ingesting MP in a small, confined cavity versus open nesters. This study highlights the usefulness of bird banding and fecal sampling to measure MP loading using larger datasets and presents indication that there is long-term retention of MP in these species. Currently, this is the most comprehensive study on MP loading in small terrestrial birds and the first time sampling the feces for MP while bird banding.