Quantifying wedge-tailed shearwater (Ardenna pacifica) fallout after changes in highway lighting on Southeast O'ahu, Hawai'i

Attraction to artificial light at night (ALAN) poses a threat to many fledgling seabirds leaving their nests for the first time. In Hawai`i, fledgling wedge-tailed shearwaters disoriented by lights may become grounded due to exhaustion or collision, exposing them to additional threats from road traffic and predation. While the timing and magnitude of shearwater fallout varies from year to year, little is known about how changing lighting and environmental conditions influence the risk of grounding for this species. We analyzed 8 years (2012-2019) of observations of road-killed shearwaters along the Kalaniana`ole Highway on O`ahu to quantify the timing and magnitude of fallout during the fledging season (November-December). Our goal was to compare fallout before (2012-15) and after (2016-19) a transition in highway lighting from unshielded high-pressure sodium (HPS) to full-cutoff light-emitting diode (LED) streetlights. To detect the shearwater response to the lighting regime, we also accounted for three potential environmental drivers of interannual variability in fallout: moon illumination, wind speed, and wind direction. The effects of these environmental drivers varied across years, with moon illumination, wind speed and wind direction significantly affecting fallout in at least one year. Altogether, the interaction between moon illumination and wind speed was the most important predictor, suggesting that fallout increases during nights with low moon and strong winds. The lack of an increase in fallout after the change from HPS to shielded 3000K - 4000K LED streetlights suggests the new streetlights did not worsen the light pollution impacts on wedge-tailed shearwaters on Southeast O`ahu. However, due to potential species-specific disparities in the behavior and light attraction of petrels, similar studies are needed before energy saving LED lights are implemented throughout the Hawaiian archipelago.

Automated summary

Attraction to artificial light at night poses a threat to fledgling seabirds. This study found that the interaction between moon illumination and wind speed is the most important predictor of seabird fallout, and changing the type of streetlights did not worsen the light pollution impacts on wedge-tailed shearwaters. However, further research is needed to determine if these findings apply to other bird species.