Reduction of coastal lighting decreases seabird strandings

Abstract Leach’s Storm-Petrels ( Hydrobates leucorhous ) are small, threatened seabirds with an extensive breeding range in the North Atlantic and North Pacific Oceans. The Atlantic population, which represents approximately 40 - 48% of the global population, is declining sharply. Positive phototaxis, the movement towards artificial light at night (ALAN), is considered to be a key contributing factor. Many seabirds exhibit positive phototaxis, which can result in stranding on land. The Leach’s Storm-Petrel is the seabird most often found stranded around ALAN in the North Atlantic, though there is little experimental evidence showing that reducing ALAN will decrease the occurrence of stranded storm-petrels. During a two-year study at a large, brightly illuminated seafood processing plant adjacent to the Leach’s Storm-Petrel’s largest colony, we compared the number of birds that stranded when the lights at the plant were turned on versus off. We recorded survival, performed carcass counts of both adults and juveniles, and released any rescued individuals. Turning the lights off reduced strandings by 39.15% (CI: 11.45% - 58.19%). The peak stranding period occurred from 25 September to 28 October, and most of the stranded birds were fledglings. These results provide evidence to support the widespread reduction and modification of coastal artificial light, especially during avian fledging and migration periods.