Multispecies HPAI spillovers led to the death of one-in-three breeding gannets

Emerging wildlife diseases, such as the recent global outbreak of Highly Pathogenic Avian Influenza, can devastate animal populations, yet identifying transmission pathways and true levels of mortality remains a formidable challenge. We leveraged European carcass counts from the severely impacted Northern Gannet, to which we fit a Bayesian, metapopulation Susceptible-Infected-Recovered-Deceased model, hence uncovering key epidemiological parameters, transmission routes, and overall mortality across the species’ 43-colony metapopulation. Within-colony transmission patterns were consistent with fixed spatial structuring of nests. Between-colony spread was predominantly distance-dependent, in-line with intra-specific transmission, though large-scale outbreak initiation was best explained by inter-specific vectors. We estimate that these multiscale/multispecies dynamics culminated in 33% continental mortality (95% CI: 27–39%) across the Gannet metapopulation. Our approach not only disentangles inter- and intra-specific transmission processes, but offers a scalable tool for real-time assessment of disease spread in wildlife, helping to control threats to biodiversity, agriculture, and public health.