Abstract
The observations of occurrence of Pterodroma externa cervicalis were carried out in the west area of North Pacific Ocean during the several cruises by R. V. Hakuho Maru as follows: KH 74-2 (30 April to 26 June, 1974), KH 74-4 (6 November to 7 December, 1974), KH 75-3 (14 May to 2 June, 1975), KH 80-2 (25 April to 18 June, 1980), KH 80-3 (14 July to 6 September, 1980), and KH 80-4 (24 September to 13 October, 1980).
1) P. externa cervicalis did not appear in the area of 30°N and northward in May and June, but this bird was found in the same area late in July. In August, the flocks of P, externa cervicalis (individual number of 2 to 15) associated with several species of tropical and subtropical sea birds, wedge-tailed shearwater Puffinus pacificus, sooty tern Sterna fuscata, white noddy Anous albus and common noddy Anous stolidus, occurred frequently in the east of Mariana Islands and they attacked the fish schools on water surface. And the flyings of solitary or two individuals of this bird scattered widely in the west area of North Pacific Ocean between 25°N and 35°N from September through November.
2) P. externa cervicalis occurred in the area where the water temperature of sea surface ranged from 20.7°C to 31.4°C, and especially this bird distributed abundantly in the area between 27°C and 30°C.
3) From those observations, it is concluded that some considerable number of P. externa cervicalis migrated regularly to the west area of North Pacific Ocean during the period from July through November.
