Permalink : http://hdl.handle.net/2115/38453

KEYWORDS : Leach's Storm-Petrel;Diet;Climatic regime shift;Sea census

Leach's Storm-Petrels Oceanodroma leucorhoa (LSTP) represent one of the smallest seabirds that feed on small micronektons available only in the surface of the sea. Therefore, they may be sensitive to the change of prey abundance. Daikoku Island (42°52'N, 144°52'E) located in the coast of eastern Hokkaido is known as one of their largest colonies. Samples of diet of LSTPs on the island were collected to examine interannual differences in diet and an at sea census of these birds was conducted in waters adjacent to the island to extract information on feeding habitats. Results of analysis reveal that LSTPs fed mainly on fish, krill, amphipods and squids. Because the change in marine ecosystem derived from 1988/89 climatic regime shift, LSPTs fed on a similar range of prey items throughout the shift. This indicates to high ability of LSTPs to search and forage a range of prey items. But lower diversity of food items in 1995 and 2003 than in 1982 and 1986 points to the potential effects of the 1988/89 climatic regime shift on the variability of prey in LSTPs. Density of LSTPs on the sea surface was significantly greater in slope (200-1000m depth) and basin (> 1,000m depth) compared to the shelf (< 200m depth). Productive and predictable upward water transportation in the slope area observed in this study probably supports the energy requirements of large number of LSTPs breeding on Daikoku Island.