From reintroduction to extinction risk: past, present and future of the newly established population of Ospreys in southern Iberia

Jorge García-Macía , Carlos Torralvo, José Manuel Sayago, María Chirino, Fidel Astudillo, Virginia Morandini, Roberto Muriel, Carlos Florencio, José Rafael Garrido, Alberto Sanabria, Miguel Ferrer

Biodiversity is declining due to the ongoing environmental global change, and raptors are among the most threatened animal groups. To counteract their decline, birds of prey have frequently been the focus of reintroduction programs worldwide. However, newly established populations must be continuously monitored to assess both short- and long-term success. In this work, we investigate the case of the Osprey (Pandion haliaetus) in Andalusia (southern Iberia), a cosmopolitan species formerly extirpated as a breeder from the western Mediterranean in the late 20th century. We used a long-term demographic and reproductive dataset (2003-2024) from the reintroduced population to investigate historical trends and long-term future population viability with VORTEX. The population increased from zero territorial pairs in 2003 to 19 in 2024. We detected three phases in the evolution of the population: establishment (2003-2008), expansion (2009-2015), and stabilization (2016-2024). During the study period, annual productivity averaged 1.09 ± 0.32 (mean ± S.D.), breeding success 79.7 ± 13.6 %, and clutch size 2.20 ± 0.75 eggs. Our baseline stochastic simulations —assuming current reproductive and demographic parameters (‘do-nothing scenario’)— suggests that Andalusian Ospreys face a serious risk of extinction within the next decades —47% within the next 40 years— driven by negative population growth. Population dynamics of the species were especially sensitive to small changes in age-specific mortality rates —particularly those of adults—, breeding performance, and first age of reproduction. These findings highlight the disproportional vulnerability of small populations of long-lived birds to small environmental changes. Specifically, they underscore the urgent need for post-reintroduction management to secure the self-sustainability of the Iberian population of Ospreys and its role as a demographic bridge within the western Mediterranean.