Using integrated wildlife monitoring for quantifying the impact of emerging Bagaza virus in red-legged partridges in Portugal, 2012-2024

Bagaza virus, a vector-borne flavivirus that causes significant mortality in wild bird species, emerged in Portugal in September 2021. This study used integrated wildlife monitoring to quantify its impact on a natural population of red-legged partridge ( Alectoris rufa ) in southern Portugal. We constructed a baseline model of population dynamics prior to the outbreak (2012-2021) and used this model to predict population size in subsequent years (2022-2024). This model, which included population abundance and demographic data of red-legged partridge, as well as climatic variables, showed a strong fit to the observed data, and the difference between the predicted and observed population size in 2022 suggests a Bagaza-induced mortality rate of at least 59% (95% CI 52-66%). In addition to enabling the adaptive management of populations, our results demonstrate that integrated wildlife monitoring offers epidemiological insights for risk assessment, highlighting its role in proactive wildlife disease surveillance within the One Health framework.