Spatially explicit risk mapping reveals direct anthropogenic impacts on migratory birds

Aim: Migratory species rely on multiple ranges across the annual cycle, rendering them vulnerable to a wide range of spatially disparate anthropogenic threats. The spatial distribution of these threats will strongly influence the magnitude of their population-scale effects, but this has not been quantitatively assessed for most species. Location: Europe, Central Asia, Western Asia, Africa. Time period: Modern. Major taxa studied: Aves. Methods: We combined remote-sensed data and expert opinion to map 16 anthropogenic threats relevant to migratory birds across Europe, Africa and the Middle East – including the first spatially-explicit pan-continental assessment of relative hunting pressure. By combining the resulting composite threat maps with species range polygons and morpho-behavioural traits-based weightings (reflecting relative threat susceptibility), we created species-specific risk maps for 103 Afro-Palaearctic migratory birds breeding in Europe and evaluated how spatial threat vulnerability relates to long-term population trends. Results: We found that greater vulnerability to direct mortality threats (including hunting pressure, infrastructure and nocturnal lights), especially in the non-breeding season, is associated with declining bird population trends. Main conclusions: Our results emphasize the importance of spatially explicit approaches to quantifying anthropogenic drivers of population declines. Composite risk maps represent a valuable resource for spatial analyses of anthropogenic threats to migratory birds, allowing for targeted conservation actions.