Seasonal Appearences of Short-tailed (Puffinus tenuirostris) and Sooty (Puffinus griseus) Shearwaters on the Tokyo-Kushiro Line, Japan

The short-tailed (Puffinus tenuirostris) and Sooty (Puffinus griseus) Shearwaters were counted from the ferry boat during eleven voyages between Tokyo and Kushiro from December 1982 to March 1984. More than 90 percent of both shearwaters were observed during the voyages from April to June, during their spring migration. The appearence of Sooty Shearwaters reached a peak in early May along the Pacific coasts of northern Honshu, one month earlier than Short-tailed Shearwaters. Their early occurrence suggests that these Sooty Shearwaters were adult birds. During the autumn migration season both shearwaters were observed to be limited in the waters off Hokkaido. Only a few birds of both shearwaters were observed in mid summer and winter. The emaciated birds of both species were observed during the voyages in mid June, 1983, but most of them were Short-tailed Shearwaters and they were also observed in late September to early October in that year.