Swinhoe's Storm Petrel

Swinhoe's Storm Petrel (Oceanodroma monorhis) is a small dark storm petrel with long wings, a shallowly forked tail and no contrasting white rump. Body shape, bill structure, plumage pattern and voice provide the strongest field characters. Age, sex and season may alter its appearance, so identification should combine several features and careful direct field comparisons with similar species in the same habitat (Wikipedia, general species account).

It forages over the north-western Pacific by taking small fish, squid and planktonic animals near the surface, and breeds colonially on offshore islands. Its movements and social behaviour vary through the year, with breeding birds generally more dispersed and non-breeding birds gathering where food is concentrated. Japanese records place it within the country's documented avifauna as a resident, migrant or visitor (Wikipedia, general species account; Wildlife of Japan occurrence records).