Breeding of Swinhoe's Storm-petrel Oceanodroma monorhis in the Kitsujima Islands, Kyoto, Japan

Marine Ornithology 38: 133–136 (2010) Breeding of Swinhoe’s Storm-Petrel Oceanodroma monorhis is only known on coastal islands in Japan, Korea, far-east Russia and China (Lee & Won 1988, Sato 1996, Kondratyev et al. 2000). Global population estimates range from 30 000 individuals (Boersma & Groom 1993) to 100 000 pairs (Birdlife International 2009), far fewer than the closely related Leach’s Storm-Petrel Oceanodroma leucorhoa (Boersma & Groom 1993). Most reports of O. monorhis are from observations or captures of birds outside breeding areas (Bailey et al. 1968, James & Robertson 1985, Bretagnolle et al. 1991, Cubitt 1995), whereas studies of the breeding biology of this species are very limited (Won & Lee 1986, Lee & Won 1988). In addition to having a limited population, some colonies of O. monorhis are threatened by human activities and introduced predators. Although several colonies are known to be active in Japan, most contain only small numbers of individuals (Sato 1996). Yoshida (1981) noted breeding of Swinhoe’s StormPetrel on the Kutsujima Islands, Kyoto, Japan, but details of this colony had remained unexamined. Because the size of the Kutsujima Islands suggested the possibility of a large breeding population, we surveyed the colony and estimated the size of the breeding population. The Kutsujima Islands (35°43′N, 135°26′E) are located in the Sea of Japan, 25 km north of the port city of Maizuru in Kyoto, Japan (Figs. 1, 2). The islands are composed of two rocky islets, surrounded by steep rocky cliffs. They extend 650 m from north to south, and their maximum width is approximately 150 m. The highest points are 89 m and 74 m above sea level on the north and south islets, BREEDING OF SWINHOE’S STORM-PETREL OCEANODROMA MONORHIS IN THE KUTSUJIMA ISLANDS, KYOTO, JAPAN