The habitat characteristics and breeding status of Leach’s Storm-Petrel on Daikoku Island, Hokkaido

Abstract

A disproportionately high number of seabird species are threatened. Particularly severe population declines have been observed in the order Procellariiformes. Understanding the nesting habitat characteristics and breeding status of such species is essential for sustainable management and conservation of breeding sites. Leach's Storm-Petrel Hydrobates leucorhous, a burrow-nesting seabird widely distributed across the Northern Hemisphere, is listed as Vulnerable by the IUCN. While habitat characteristics and breeding ecology are relatively well studied for Atlantic populations, such information remains scarce for the Pacific population even though one of the largest known colonies breeds on Daikoku Island, Hokkaido. We investigated the nesting habitat and breeding status of Leach's Storm-Petrel on Daikoku Island in eastern Hokkaido, Japan. During the 2021 and 2022 breeding seasons, we mapped vegetation across the island, established multiple 2 m × 10 m study plots across five dominant plant species, and recorded burrow density, soil hardness, soil texture, and slope within each plot. Additionally, we assessed burrow occupancy rates during five years between 2009 and 2024. Our results revealed that burrow density was negatively associated with soil hardness and positively associated with slope. Although overall trends in burrow density by vegetation type were consistent with previous studies, the plant species with the highest burrow densities differed. Burrow occupancy rates varied greatly among years, suggesting interannual variation in the likelihood of breeding success or failure. These findings enhance understanding of habitat selection and reproductive dynamics in a Pacific population of this vulnerable species and provide a foundation for future conservation efforts.