Spectacled Tern

Spectacled Tern (Onychoprion lunatus) is a dark-backed tropical tern with white forehead and a broad black eye mask resembling spectacles. 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 comparisons with similar species in the same habitat (Wikipedia, general species account).

It feeds on small fish and squid over tropical seas and nests colonially on remote oceanic 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).