Wilhelm, Sabina
Behavioural Responses of Nocturnally Stranded Seabirds Toward Artificial Light, and Implications for Rescue Programs
Globally, fledglings of more than 50 seabird species are vulnerable to stranding in human settlements near their colonies as they leave their nests for the first time. This phenomenon has been attributed to attraction toward and disorientation by artificial light at night (ALAN). Grassroots rescue programs find more birds in illuminated locations than in dark ones, but it is unclear to what extent this pattern is driven by seabird versus rescuer behaviour. I studied behavioural responses to ALAN in stranding-prone Atlantic puffin (Fratercula arctica) and Leach's storm-petrel (Hydrobates leucorhous) fledglings and investigated detection probabilities of 3D-printed puffin fledgling decoys by rescuers. I hypothesized that seabird strandings are due to attraction toward ALAN; that post-stranding behaviour varies with taxon and lighting conditions; and that post-stranding behaviour (e.g., concealment) and lighting conditions drive variance in detection probability of stranded seabirds by rescuers. To address my first hypothesis, I alternately illuminated two beaches near a Newfoundland puffin colony and found significantly more puffin fledglings stranded when the beaches were illuminated than when they were dark, supporting the light attraction hypothesis. Stranded puffins similarly moved toward light over darkness in a Y-maze choice experiment and were less active under LED light than in darkness or under high-pressure sodium light, demonstrating a preference toward certain light conditions post-stranding. In contrast, storm-petrels predominantly avoided lit conditions in a Y-maze and were less active in darkness than under light. Further, when provided with a place to hide, more than half of storm-petrels concealed themselves when in light conditions versus none in darkness. To test my third hypothesis, I deployed puffin decoys and found that rescuers detected them more easily in higher light levels, in less concealed locations, and with increased search effort. My results support historical deductions that seabird fledgling strandings are caused by attraction toward artificial light but demonstrate that post-stranding behavioural responses to ALAN depend on species and light type, which may in turn affect detection probability by rescuers.
Author Keywords: artificial light, atlantic puffin, charadriiform, Leach's storm-petrel, light attraction, procellariiform