Bulwer's Petrel

Bulwer's Petrel (Bulweria bulwerii) is a small, slender, uniformly dark petrel with long pointed wings and an elongated, graduated 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 spends most of its life over warm oceanic water, taking squid, small fish and planktonic prey from near the surface, and nests in cavities or crevices on remote 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).