Migratory birds as global vectors and evolutionary incubators of antibiotic resistance genes

The global antimicrobial resistance (AMR) crisis, fueled by the cross-border dissemination of antibiotic resistance genes (ARGs), poses a critical and escalating threat to public health. Migratory birds, with their extensive mobility and broad ecological connectivity, effectively bridge human-influenced and natural ecosystems, thereby playing a key role in the worldwide circulation of ARGs. While significant advances have been made in detecting ARGs in birds and tracing their links to anthropogenic sources, research remains fragmented: birds are often regarded merely as passive samplers, without due consideration of the mechanistic processes through which ARGs are acquired via avian traits, evolve within gut microbiomes, and are disseminated across continents through migratory networks. This review synthesizes current evidence to position migratory birds not only as global vectors but also as evolutionary incubators of ARGs. Integrating ecological, microbiological, and One Health perspectives, we delineate the pathways of bird-mediated ARG transmission across multiple scales—from molecular events within the avian gut and individual-level traits, to population-level migratory networks, and up to global flyways. A particular focus is placed on the gut microbiome, where mobile genetic elements (MGEs) serve as crucial drivers of ARG reassortment, stabilization, and horizontal transfer, thereby bridging micro-scale genetic mechanisms with macro-scale ecological spread. Looking forward, we recommend future studies to quantify ARG fluxes at key stopover sites, clarify the role of under-represented migratory taxa, and develop predictive frameworks that integrate avian movement ecology with resistome surveillance. We advocate for integrated One Health strategies and propose the Flyway-Node-Resistome (FNR) Framework as a basis for future research and transnational governance, aimed at mitigating AMR spread while conserving migratory bird populations.