Wedge-tailed Shearwater Ardenna pacifica
Status : Locally common
Distribution : Local breeder (Mar-Dec; laying and incubation in June, hatching in Aug, fledging in Nov) on islands off far south of Honshu (Tori-shima, Izu Islands; Ogasawara Islands; Volcano Islands). About 100 nests on Tori-shima, Izu Islands (環境省 2021); presumed 13,608 nests (about 41% were used) on Kitano-shima, presumed 5,264 nests (about 65% were used) on Mukojima-tori-shima, 2,167 nests on Muko-jima, 2,363 nests on Nakodo-jima, 2,330 nests on Yome-jima Mukojima Islands (環境省 2021b, 鈴木ほか 2019); breeding on Higashi-jima, Nishi-jima and Minami-jima Chichijima Islands but poorly known recently (川口ほか 2013); 40 nests on Mukoh-jima, 40 nests on Hira-jima, 20 nests Ane-jima, 10 nests on Imohto-jima, 60 nests on Mei-jima, the number of nests is unknown but some pairs breed on Minami-zaki Hahajima Islands (川口ほか 2013); 30 pairs breed on Nishino-shima (川上＆小山田 2020); presumed several hundreds pairs breed on the coast line of Minami-iwo-to (川上ほか 2021). There is the record of breeding on Kita-iwo-to in the past but there were no breeding birds on Kita-iwo-to when the survey conduced in 2019 (川上ほか 2021).
Common around breeding islands year-round. Regularly seen off the Pacific coast and East China Sea coast of Tokara Islands (Kagoshima Pref.) and Sakishima Islands (Okinawa Pref.) mainly in Mar-Oct and poorly known in winter.
Tips : Almost all of the birds around Ogasawara Islands is light morph. Dark morph is rare in the area. Breeding birds in Ogasawara Islands are only light morph. Not only light morph but also dark morph are seen regularly around Tokara Islands and Sakishima Islands. Most of the dark morph birds around Tokara and Sakishima Islands wing molt in July. Dark morph birds were seen off north of Izu Islands. These birds may move along the Kuroshio Current from Sakishima Islands to Izu Islands.
There are some records at off the Pacific coast of Aomori Pref. and Iwate Pref. These records are tend to be increased when the sea temperature is high or strong east wind is blowing. There are records in other areas of Japan after typhoons passed.
環境省(2021). 2020度モニタリングサイト1000小島嶼(海鳥)調査報告書. 環境省自然環境局
環境省(2021b). モニタリングサイト1000小島嶼(海鳥)調査 2004-2018年度とりまとめ報告
ドリPuffinus pacificusの繁殖確認. 小笠原研究年報, 36: 79-82.
Ogasawara research, 44: 217-250.
川上和人・小山田佑輔(2020). 2019年における西之島の鳥類相. Ogasawara research, 46:
川上和人・鈴木 創・堀越 宙 (2021). 2019年における北硫黄島の鳥類相. Ogasawara
research, 47: 185-200.
鈴木 創・堀越和夫・佐々木哲朗・川上和人(2019). 小笠原諸島聟島列島におけるノヤギ排
除後の海鳥営巣数の急激な増加. 日本鳥学会誌, 68(2): 273-287.