A meteorological consideration on the breeding places and migration of Diomedea albatrus

Abstract

The reported breeding places of Diomedea albatrus have been: 1. Torishima, Izu Is., 2. Some islands of the Bonin Is., 3. Kobisho, Senkaku Is., 4. Agincourt I. and 5. Pescadores I. The environmental conditions common to these breeding islands are: a) Safety especially from man, being non-inhabited islands or nearly so and very hard to access. They have however not abandoned Torishima after a long lasted slaughter. b) Coasts are steep cliffs of more than 5 meters. c) Highest altitudes are less than 200m (but 400m at Torishima) and the islands are alway flat type, with the area of less than 5 square km. d) No, or few tall trees at the most and without forest on any of the islands. e) Often with dense grass less than two meters high and rather extensive sandy slope existing among them. f) The breeding islands are scatterd in subtropical belt within 119°-145° E, 24°-30° N. g) These islands are within or adjacent to the warm currents and they feed on fishes of these currents.The meteorologically, these islands are in a temperature zone with average more than 12°C and less than 28°C, humidity more than 70% (though this preference is doubtful), rainfall less than 180mm which is relatively less than in other subtropical islands, while fine-cloudy ratio is considered of little significance.The above islands are in the zone of seasonal winds, with the velocity frequently more than 10m/sec., blowing from the Asian continent with prevailing NE local winds, rather than NW. These winds may also influence the movements and distributions of food fishes, as well as aiding the leaving and arriving of the albatrosses of the islands.Special descriptions of the environments of Torishima where D. albatrus and D. nigripes are segregated by habitat (the former in grassy and the latter on sandy places) are given.They arrive Torishima in October-November and leave in April-May. In the autumn, the NE winds become prevailed from E. Asiatic High and breeding islands are included in the temperature belt of average 23°-26°C (Fig. 3, a). In the spring, North Pacific High becomes prevailed causing the SW winds and the breeding islands are in the belt of 23°-25°C (Fig. 3, b). Their pelagic movements and migrations should also be correlated with such oceanic winds and temperatures.