25 years of light-induced petrel groundings in Reunion Island: Retrospective analysis and predicted trends

Abstract

Artificial lights are known to induce mass mortality of petrels. This study analyzes this phenomenon in Reunion Island, where four species are impacted: the endemic Barau’s petrel ( Pterodroma baraui ) and Mascarene petrel ( Pseudobulweria aterrima ), the tropical shearwater ( Puffinus bailloni ) and the wedge-tailed shearwater ( Ardenna pacifica ). 40,036 birds were found grounded between January 1996 and December 2021, most of which were fledglings. Spatial distribution of groundings matched with the distribution and intensity of light pollution. With a mark and recapture method, we estimated that at least 3.93 % of Barau's petrels fledglings are affected by light-induced groundings each year. This method was also used to estimate Barau’s Petrel population around 33,000 breeding pairs. Time series analyses showed strong positive trends of the number of groundings for all species, which were positively correlated with the intensity of light pollution. All species showed a seasonal increase in groundings coinciding with their fledging periods. Interannual variations of Barau's petrel and wedge-tailed shearwater groundings were explained by moon phase at their fledging peaks. We built statistical models to explain year-to-year changes in the number of groundings for each species, and used them to predict the number of groundings in the next decades. We predicted that up to 87,000 petrels may be found grounded from 2022 to 2050 if nothing is done to reduce light pollution. These results and predictions underline the urgent need to strengthen the rescue campaign and to implement strong light reduction measures. • 40,036 petrels were found grounded on Reunion island between 1996 and 2021. • The local rescue campaign successfully released 88.2 % of these birds. • Light pollution is the main factor explaining the increase in petrel groundings on Reunion island. • At least 3.93 % of Barau's petrels fledglings are grounded by light pollution. • Up to 87,000 petrels may be found grounded on Reunion island from 2022 to 2050.