HPAI drives a fourfold increase in adult gannet mortality which requires two decades recovery time

Wildlife disease outbreaks are increasing, representing a growing threat to biodiversity. Despite this, their demographic cost and recover times are poorly quantified. In 2021, HPAI H5Nx viruses entered new wild host groups, infecting colonial seabirds and triggering substantial global die-offs. Here, we estimate annual survival of adult Northern gannets (Morus bassanus) before and after the 2022 outbreak, using longterm (15-year) capture-mark-recapture data from two large UK colonies, and predict post-outbreak time to recovery using a metapopulation state-space model. Adult mortality averaged 6% and 11% (at Bass Rock and Grassholm, respectively) in the 11 years prior to 2022 but increased sharply to ∼ 33% and 47% during the HPAI outbreak. Integrating these survival rates into our metapopulation model predicted 26% and 38% decreases in colony size in 2023, and that colonies will only recover to the pre-2022 levels by 2041, 19 years after the outbreak. Monitoring of key life history traits such as adult survival and integrating these estimates into realistically complex population models is paramount to generate robust evidence for seabird conservation planning, management and mitigation for seabirds. Specifically, we recommend revising the global conservation status of Northern gannets in the light of this unprecedented mortality and subsequent population recovery time from a single disease outbreak.