Microplastics and terrestrial birds: a review on plastic ingestion in ecological linchpins

Microplastic (MP; plastics 5 mm or less) pollution appears to be ubiquitous, leading to concerns on how MPs affect organisms. While some plastics are manufactured at a small size, most MPs are broken down from larger plastics with often unknown origin. With documented risks of intestinal blockage, false satiation, and developmental dysfunction in organisms, understanding how MPs move through food webs is imperative to determine what organisms may be predisposed to MP pollution and where to focus regulations. Terrestrial birds have the potential to strategically inform researchers about MP pollution, since they are incredibly diverse, span many different habitats and behaviors, and are readily accessible to study. However, research is lacking for how important this group is as ecological indicators, with most studies focused on aquatic birds and those that exist on terrestrials focus on larger raptors. This review details the origins of MPs, their potential toxicity, movement through the environment, and our understanding of the role terrestrial birds play in ingestion and movement of MPs. Research on this topic is increasing, with plastics found in almost all terrestrial species that were sampled in the reviewed studies. Recent findings and future interests are focused on the varying levels of MPs in terrestrial bird species, likely due to individual behavior, morphology, and daily habitat use.