Fork-tailed Storm Petrel

Fork-tailed Storm Petrel (Hydrobates furcatus) is a bluish-grey North Pacific storm petrel with darker flight feathers, a pale face and a distinctly forked tail. 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 takes plankton, small fish and squid from the sea surface, often pattering with its feet, and lays a single egg in a rock crevice or burrow. 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).