Mortality at wind-farms is positively related to large-scale distribution and aggregation in griffon vultures

Wind-farms have negative impacts on the environment, mainly through habitat destruction and bird mortality, making it urgent to design predictive tools to use in landscape planning. A frequent assumption of wind-farm assessment studies is that bird distribution and abundance and bird mortality through collision with turbines are closely related. However, previous results are contradictory and question the usefulness of these variables to select safer wind-farm locations. We focused on a species highly vulnerable to collision at wind-farms, the griffon vulture, to test whether mortality at turbines was related to the relative position of turbines within the vulture population. We used the location of all turbines on 34 wind-farms in southern Spain, details on 342 griffon vultures found dead, and the location and size of breeding colonies and roost sites of the species during the breeding and non-breeding seasons, respectively. Using variables that describe the large-scale distribution and aggregation of vultures, we found that year-round mortality at turbines increased when they were located in highly populated areas, a result that can be translated into management guidelines to plan wind-farm locations. Bird abundances can help to guide wind-farm plans at large scales. Current protocols of counting birds at specific points during particular periods of time have low predictive power. However, other more integrative cues such as the spatial distribution and aggregation of some vulnerable species should be used as criteria for large-scale environmental planning. Local inspection of the relationship between mortality at existing turbines and their relative position within the spatial distribution of bird populations can guide managers in planning future wind-farms and in managing currently operating developments.