Shorebirds ingest plastics too: what we know, what we do not know, and what we should do next

Concerns about the impact of plastics pollution on the environment have been growing since the 1970s. Marine debris has reportedly entangled and (or) been ingested by 914 marine species ranging from microinvertebrates to large marine mammals. Shorebirds have a high potential to be exposed to and ingest plastics pollution, as many species migrate long distances and periodically concentrate around shorelines, coastal areas, and estuaries that can have elevated levels of plastics pollution. Currently, little is understood about plastics exposure, frequency of occurrence (FO), and potential impacts relating to shorebirds. In this study, we catalogued and reviewed available studies across the globe that examined plastics pollution in shorebirds. We then quantified relevant traits of species and their environments to explore how shorebirds may be exposed to plastics pollution. Of 1106 samples from 26 shorebird species described within 16 studies that examined plastic ingestion, 53% of individuals contained some form of plastics pollution. Overall, Haematopodidae (oystercatchers) had the highest FO of plastics, followed by Recurvirostridae (avocets), Scolopacidae (sandpipers, phalaropes, godwits, and curlews), and Charadriidae (plovers). Plastics FO was much greater among species that migrated across marine areas (either oceanic or coastal) than those species that used continental flyways. Species that foraged at sea, on mudflats, or on beaches had higher average FO of plastic ingestion than species that foraged in upland or freshwater environments. Finally, species that used a sweeping foraging mode showed higher levels of ingested plastics and contained a far greater number of plastic pieces than all other techniques. These conclusions are based on a limited number of species and samples, with the distribution of samples skewed taxonomically and geographically. Using the combined knowledge of known shorebirds-plastics interactions and shorebird ecology, we present a hierarchical approach to identifying shorebirds that may be more vulnerable and susceptible to plastic ingestion. We provide recommendations on sampling protocols and future areas of research.