Contrasting vital rate contributions across interconnected populations of a highly vagile avian scavenger: A multisite modelling approach

Identifying the key drivers of population dynamics in long-lived species is critical for understanding their life history and guiding conservation. However, dispersal processes like immigration and emigration are often overlooked in long-term studies of highly vagile, transboundary species such as vultures, despite their role on population trends. Additionally, estimating often-neglected population fractions like non-breeders is essential to assess trends accurately, especially in species of conservation concern. Using the Eurasian griffon vulture (Gyps fulvus) as a model species, we assessed the dynamics of three neighbouring populations in northeastern Iberia (Catalonia -CAT-, Aragon -ARA-, Valencian Community -VAL-) over 14 years using a Bayesian multisite Integrated Population Model (ms-IPM), explicitly incorporating movements between regions. Results showed distinct trends: steady growth (CAT), stabilization (VAL), and decline followed by stabilization (ARA). Adult survival was the key driver of population growth in ARA, despite being the lowest (0.94 vs. 0.97 in VAL and 0.98 in CAT), likely due to mortality from windfarms and electrocution. In contrast, the floater (non-breeder)-to-breeder ratio and immigration were more influential in CAT and VAL, but both were negatively correlated with population size across regions, indicating density dependence. In VAL density dependence suggested that the population was approaching its carrying capacity, increasing dispersal. Our study highlights the importance of ms-IPM for understanding complex demographic processes, such as the role of dispersal and non-breeders, in population dynamics of wide-ranging species. We provide a comprehensive framework to account for spatial and demographic heterogeneity, aimed at improving vulture conservation at both local and transboundary scales.