Microplastics are small plastic particles of less than 5 mm in length that can contaminate terrestrial, aquatic and air environments. Their abundance is highly concerning, as they can have a negative impact on the health of living organisms. Previous studies reported that microplastics could change the gut microbiome and impact the overall health of laboratory mice. However, the impact of microplastic pollution on the gut microbiome of wild populations is unknown. In this study, Fackelmann et al. explored the effects of microplastic chronic ingestion in two seabird species — Cory’s shearwaters (Calonectris borealis) and northern fulmars (Fulmarus glacialis). The authors obtained samples from the proventriculus and cloaca to analyse the microbiome in different parts of the birds’ gastrointestinal tracts. They performed 16S ribosomal RNA gene sequencing and found that microplastics affected the microbial diversity and composition of both seabirds’ gastrointestinal microbiomes. Increased microplastics ingestion was linked to a reduced commensal microbiota, and an increase in pathogens such as Clostridium perfringens, Parvimonas spp. and Fusobacterium spp., as well as other antibiotic-resistant and plastic-degrading microorganisms. Whether microplastics can impact the gut microbiome and health of other wildlife species and humans is unknown and warrants further investigation.