Linking favourability models with breeding output: a modelling approach to improve management and conservation actions for a threatened avian scavenger

In the current period of unprecedented global change, urgent action is needed to establish proactive management strategies for vulnerable species. The obligate avian scavenger guild is a group that provides important ecosystem services and 80 % of the species within the group are threatened. In this study, we applied species distribution models incorporating the favourability function to the threatened bearded vulture (Gypaetus barbatus), to predict the best areas for this species in NE Spain, the home of nearly 50 % of its European breeding population. The model incorporated various environmental variables, including the sheep stocking rate as a proxy for food availability. We also correlated environmental favourability with breeding performance (productivity, breeding success and mating behaviour) taken from 141 reproductive territories, compiled over the last 10 years. Five variables were supported in the favourability model: steepness of slope, distance to an unpaved road, surrounding human population density, minimum temperature, and sheep stocking rate. Favourability was positively correlated with productivity and breeding success, suggesting that high quality habitats are associated with high breeding performance. Regarding the association between environmental favourability and mating behaviour, we found that environmental favourability was only marginally statistically significantly correlated with the event of polygamous reproductive trios. Considering the prevailing environmental conditions, including topography, land use, and livestock density, our findings suggest that NE Spain still has unused potentially suitable breeding sites for the future geographical expansion of the species. Our results identified specific areas that should be prioritized for future landscape protection, management, and conservation action.