The Qinghai-Tibet Plateau serves as a critical hub along the Central Asian Flyway (CAF) and a recognized hotspot for the emergence of highly pathogenic avian influenza (HPAI) viruses. Despite recurrent outbreaks, the migratory dynamics of key reservoir species, such as the Brown-headed Gull (Chroicocephalus brunnicephalus) and their potential contributions to viral dissemination remain poorly understood. Here, we integrated high-resolution GPS telemetry with Bayesian phylogeographic analyses to investigate the potential association between migration and HPAI H5Nx virus spread. Based on tracking data from 11 individuals, we identified 5 major life-history stages and 12 important stopover sites used during migration, including 6 in autumn and 6 in spring, and characterized their spatiotemporal distribution patterns. Phylogenetic reconstruction showed that three independent introductions of HPAI H5Nx viruses occurred on the Qinghai-Tibet Plateau between 2021 and 2024, all involving strains associated with Brown-headed Gulls and classified into the 2021-H5N8 I, 2021-H5N8 II, and 2022-H5N1 clusters. These viral clusters were distributed primarily along the CAF and the East Asian–Australasian Flyway (EAAF), with diffusion patterns broadly consistent with the spatiotemporal dynamics of migratory birds. Notably, the spread of the 2022-H5N1 cluster along the CAF was highly concordant with the migratory route and phenology of Brown-headed Gulls, while host transition analysis suggested that gulls may serve as bridging hosts in interspecies transmission. Together, these findings suggest that Brown-headed Gulls may contribute to the cross-regional dissemination and interspecies transmission of HPAI H5Nx viruses, and highlight the value of combining tracking data with viral genomics for cross-border surveillance.