Migratory birds at the intersection of ecology and public health: Disseminating critical antimicrobial resistance genes across the globe

Antimicrobial resistance (AMR) is a critical global health threat, and migratory birds have emerged as unexpected yet key players in its ecology and dissemination. Acting as both reservoirs and long-distance vectors. This review uniquely integrates evidence on the role of migratory birds in the global spread of “critical priority” antimicrobial resistance genes (ARGs), including bla _CTX-M (ESBLs), carbapenemases (bla _NDM, bla _KPC), mcr-1 (colistin), and tet (X4) (tigecycline). We advance a three-step causal hypothesis comprising contaminated stopover acquisition, migration-assisted persistence, and shedding at distant receptor habitats. We further apply operational criteria to distinguish true vector species from sentinels and reservoirs: vectors are defined by longitudinal detection across multiple flyway nodes with evidence of viable shedding enroute; reservoirs by persistent colonization independent of migration; and sentinels by transient, locally acquired contamination. These criteria provide a framework for linking molecular resistance determinants to global migratory flyway connectivity. Unlike previous reviews that largely describe local or regional occurrences, we provide a structured comparative synthesis across all major flyways, revealing that scavenging bird guilds and proximity to anthropogenic contamination are the principal determinants of AMR prevalence, rather than flyway geography. Additionally, we highlight the role of mobile genetic elements (MGEs), e.g., plasmid replicon types, to assess whether MGEs in avian isolates mirror those in clinical settings; we observe substantial overlap for IncI2, IncX4, and IncFII replicons. Consequently, we identify the systematic comparison of avian versus clinical MGE profiles as a priority research gap, given their role in facilitating horizontal gene transfer and further amplifying resistance dissemination. By integrating published data from diverse geographic regions across Asia, Europe, the Americas, and Australia, this review advocates the urgent need for a three-tier, flyway-based surveillance framework specifying target species (Larus spp., Ardea spp., Anser spp.), sampling seasons (post-breeding migration), minimum sample sizes (n ≥ 50/site/season), priority resistance markers (bla _CTX-M, mcr-1 , bla _NDM), and international data-sharing mechanisms through WHONET, EAAFP, and CMS. These advances move the field from descriptive catalogue towards a mechanistically grounded, operationally actionable One Health framework for managing AMR at the wildlife-environment interface. © 2026 The Authors.