Changing vertical substrate color and pattern to reduce seabird collisions associated with artificial light

Abstract The magnitude and extent of increased artificial light at night is a growing concern for various species and ecosystems, including procellariiform seabirds. Artificial light on coastlines, ships, and fossil fuel platforms attracts procellariiforms that are foraging or migrating at night, causing fallout at illuminated sites that lead to fatalities through exhaustion, dehydration, predation, vehicle collisions, and impact injuries. To assess effects of different illuminated vertical substrates on collisions, we suspended different colored (white, black, and beige) and patterned (plain, grid, and striped) cloth sheets in a colony of Hydrobates leucorhous (Leach’s Storm-Petrel) on 40 nights in 2024 and 2025. Sheets were illuminated with a white floodlight using 5-min on/off intervals, and sheet treatment was changed every 30 min. Petrels were 9 times more likely to collide with colored sheets when lights were on rather than off, nearly 3 times more likely to collide with white than black sheets, and between 2 and 3 times more likely to collide with plain than patterned sheets. Despite decreased collisions with darker sheets, petrels flying overhead were noticeably repelled by light, offering support for the hypothesis that artificial light causes disorientation rather than attraction at small spatial scales. Dark colors or patterned walls could reduce fallout and collisions for seabirds as well as for migrating passerines and could have implications for conservation of other organisms affected by artificial light.