Aleutian Tern

Aleutian Tern (Onychoprion aleuticus) is a slender grey tern with black cap, white forehead, black bill and feet, and a dark bar across the secondary feathers. 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 breeds colonially on subarctic coasts in Alaska and eastern Siberia and migrates to tropical western Pacific waters. Its movements and social behaviour vary through the year, with breeding birds generally more dispersed and non-breeding birds gathering where food is concentrated. The Korean vertebrate catalogue used for this guide records the species in South Korea (Wikipedia, general species account; Wildlife of Korea occurrence records).