(1) Ozawa (1966) reported the Brown booby,
Sula leucogaster ranged as far north as Kusagaki-jima and Sumisu-to, froming the northernmost limit of its breed-ing range, likely on the latter island, in the North-west Pacific Ocean. After that, observations of the Brown booby and other species around these islands were carried out by two ships, the Umitaka Maru and Seiyo Maru, of the Tokyo University of Fisheries. The Umitaka Maru cruised around Kusagaki-jima in July, 1967 and Tori-shima west of the Danjyo-guntto in August 1967. Sumisu-to was observed by the cruises of the Seiyo Maru in July, 1966 and July, 1967 as well as by the Umitaka Maru in February, 1968. The Umitaka Maru cruised around Sofu-gan lying approximately 40 miles south of Tori-shima, Izu-retto on her way northward to Sumisu-to on February 18, 1968.
(2) In total 1669 Brown boobies consisted of 6 individuals and 50 flocks were recorded at sea from 42 miles east of Kusagaki-jima westward to the Islands during the period of 1600-1900 (Sunset time) July 23, 1967. The Brown booby flying towards the Islands (nesting place) increased in percentages and the average number per flock decreased as the island was near and the Sunset closed.The distance (mile), then the Brown booby came in sight without an aid of binocular, in relation to the number of the birds in a flock (n) was estimated: D (mile)=0.7 n 0. 19
(3) A total of 5 Brown boobies was recorded around Tori-shima lying 18.5 milesnorth-west of the Danjyo-guntto, west of Kyushu on August 6, 1967.
(4) The birds recorded around Sumisu-to, in July 1966 were 80 individuals in total of Sooty tern,
Sterna fuscata and Common noddy,
Anous stolidus and then no Brown booby. In July 1967, 7 Brown boobies and a total of 64 individuals of Sooty tern and Common noddy were observed. In February 1968, 15 individuals of the Brown booby were sighted at all.
(5) No birds were seen around Sofu-gan in February 18, 1968.
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