Leach's Storm Petrel

Leach's Storm Petrel (Hydrobates leucorhous) is a small dark storm petrel with a forked tail and a contrasting white rump divided by a darker central line. 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 spends much of the year over cool ocean waters, takes planktonic prey near the surface and visits island burrows and crevices mainly after dark during breeding. 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).