Under Cover of Darkness: Refuge from Artificial Light at Night may Mitigate Risks to Stranded Seabirds

ABSTRACT Artificial light at night is an anthropogenic pollutant that has wide-ranging effects on wildlife. Fledgling seabirds of the order Procellariiformes exhibit phototaxis toward artificial lights on their first flights from the nest, causing them to become grounded in human settlements where they are subject to increased risk of predation. Limited evidence suggests that certain light types may be less attractive than others, yet there is also evidence for an aversion to light under certain circumstances. We investigated differences in phototactic behaviour, activity level, and shelter-seeking behaviour of grounded Hydrobates leucorhous (Leach’s storm-petrel) fledglings exposed to artificial light in three experiments: a Y-maze choice experiment, an open field test, and a modified open field test with a hide box provided (“Safe Haven test”). When provided with combinations of different light types in the Y-maze, storm-petrels typically remained stationary in the darkest part of the apparatus and exhibited no response toward one light type over another. This was consistent with results from the open field test, in which individuals were less active in darkness than when exposed to two out of three light conditions (Warm White Light-Emitting Diode and High Pressure Sodium). More than half of birds entered the hide box in light conditions, compared to none in the dark. Considered together, our results indicate Leach’s storm-petrel fledglings exhibit photophobic behaviour after stranding, which may be part of a behavioural strategy to avoid predation. Further, we demonstrate the utility of providing hide boxes to protect stranded seabird fledglings in locations where lighting cannot be eliminated or where rescue efforts may be limited in spatial or temporal coverage. However, hide boxes would have limited utility in dark locations. Hide boxes constitute a novel mitigation measure that merits future testing for its ability to reduce stranding-induced mortality, especially in imperiled procellariiform species. LAY SUMMARY Globally, fledglings of many seabird species become stranded in towns and at industrial sites near their breeding colonies Strandings are thought to be caused by attraction to lights, although some species appear to avoid light We tested behavioural responses and activity levels of Leach’s storm-petrel fledglings toward several different light types When presented with different types of light in a choice experiment, most birds remained stationary Fledglings were more active in warm-hued lights than in darkness Birds sought shelter when it was provided in light conditions, but not when provided in darkness Our results suggest that rescue programs targeting Leach’s storm-petrels should include searches in dark, hidden locations where fledglings are likely to hide, and support the use of small shelters to protect stranded seabirds when lights cannot be turned off

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