From colony to fallout: Artificial lights pose risk to seabird fledglings far from their natal colonies

Abstract

Seabirds are at risk of decline from multiple threats, including artificial light resulting in their grounding (“fallout”). Without evidence, it can be assumed that seabirds travel short distances from natal colonies to their fallout location, potentially to the closest light source. To test this, a case study on wedge-tailed shearwaters (Ardenna pacifica, ʻUaʻu kani) fledging from the island of Oʻahu, Hawaiʻi was conducted. To assess fallout locations in relation to natal colonies, we affixed identification bands to 4648 chicks at nine natal colonies prior to fledging from 2018 to 2022. Distances between fallout location and natal colony were mapped and fallout location characteristics (radiance, elevation, distances to nearest coastline, road, and colony) were analyzed for 27 banded fledglings that were discovered post-fallout. The distance between the natal colony and fallout location was significantly greater than the distance between the nearest colony and the fallout location. Fallout often occurred on opposite coastlines from the natal colonies and at substantial distances (x¯ = 24.91 km), with one fallout event recorded on a different island from the natal colony. Our results demonstrate that all artificial lights, regardless of proximity to seabird colonies, may pose a threat to seabird fallout and that fallout is often occurring far from natal colonies and in inconsistent patterns. Collaborative, large-scale, and multi-island light management alteration, particularly during fledging periods, is critical in recovering Pacific Island seabird populations. Actions such as these will benefit not only light-sensitive species such as seabirds and sea turtles but also human health and night-sky viewing.