Long-term effects of hydropower development on cliff-nesting raptors in a mediterranean landscape

Hydropower is often promoted as a sustainable solution for meeting rising energy demands while reducing greenhouse gas emissions. However, its impacts on terrestrial wildlife remain poorly understood, even in the case of threatened and declining species such as cliff-nesting raptors. This study assesses the long-term impacts of hydropower development in northeastern Portugal on three cliff-nesting raptors: Golden eagle ( Aquila chrysaetos ), Egyptian vulture ( Neophron percnopterus ), and Griffon vulture ( Gyps fulvus ). Besides the dam impacts, these species were also potentially affected by mitigation measures, including prey management for eagles and the establishment of feeding stations for vultures. Using a Before-After-Control-Impact (BACI)-like approach, we analysed changes in territory occupancy, breeding population size, and breeding productivity before (2010–2014) and after (2015–2022) river damming. The extent of flooding around nests served as a proxy for dam impact severity. The Golden eagle population fluctuated, and breeding productivity declined over time, though without a clear link to flooding. Egyptian vultures showed steeper productivity declines in territories most affected by flooding. Conversely, Griffon vulture occupancy and population size increased after flooding, albeit with a weak tendency towards a smaller population increase where flooding was greater. Our findings highlight species-specific responses to hydropower development. While Griffon vultures likely benefited from supplementary feeding, Egyptian vultures may have been negatively affected by habitat loss and competition with the former species. These contrasting trends highlight the complex ecological consequences of hydropower infrastructure and underscore the need for species-focused mitigation strategies. The study emphasizes the importance of long-term monitoring and adaptive management to balance renewable energy development with the conservation of vulnerable wildlife.