Countdown to extinction: Role of invasive wild boars in the population dynamics of the Yelkouan shearwater ( <i>Puffinus yelkouan</i> ) on Port‐Cros Island

Abstract The Yelkouan shearwater, Puffinus yelkouan , is an endangered Mediterranean endemic species of ground nesting burrowing birds. The Yelkouan shearwaters living in the Port‐Cros National park, which encompasses the Porquerolles, Bagaud, Port‐Cros and Le Levant islands, represent 95% of the French population. Previous studies demonstrated that Port‐Cros Island is a sink sustained by immigration. Wild boars are recent invaders on Port‐Cros Island. We investigated the negative impacts of invasive wild boars on Port‐Cros shearwaters by monitoring the nests and using a population model derived from long‐term monitoring of the Yelkouan shearwater population at a reference colony. Our results confirm that wild boar prey on shearwaters and destroy their eggs and nests. Wild boar caused an average mortality of 20 [95% CI: 0; 47.3] Yelkouan shearwater chicks per year from 2019 to 2024 on Port‐Cros Island; the overall mortality due to wild boar in the whole Port‐Cros National Park was estimated at 75 [95% CI: 0; 177.5] per year from 2019 to 2024. Furthermore, the number of potential nesting burrows decreased by 35% due to trampling and crushing by wild boar, causing habitat loss. The shearwater reproduction success rate was significantly reduced due to wild boar impact. Based on matrix population model, we calculated that the wild boar impact on the Yelkouan shearwater would significantly hasten its extinction on Port‐Cros Island. Measures to control the number of wild boars help to limit this impact. Nevertheless, the population of Yelkouan shearwaters in Port‐Cros National Park is declining in all scenarios. This could lead to local extinction within a few decades unless immigration reinforces the population. Solution : Wild boar population eradication would help protect the population of shearwaters but will not be sufficient to stop the decline of Yelkouan shearwaters on Port‐Cros Island.