Records of Wedge-tailed Shearwater and Swinhoe's Storm Petrel Around the Nansei Islands

Wedge-tailed Shearwaters Ardenna pacifica and Swinhoe's Storm Petrels Hydrobates monorhis are passage migrants around the Nansei Islands, Japan. However, their detailed distribution in relation to breeding sites have not been thoroughly investigated. We summarized their records collected during our surveys conducted from July to September between 2009 and 2024 and the historical records of photograph and specimens. Most of Wedge-tailed Shearwaters (97% of 537 individuals at 41 observations) were the dark morph; suggesting that most individuals migrating to the waters around the Nansei Islands likely originate from breeding populations in the regions south of 10°N. A total of 10 observations, including 30 individuals, of Swinhoe's Storm Petrel were recorded mainly during their breeding season and some of them showed molt patterns of breeding adults, suggesting the possibility of breeding in the Nansei Islands.