Greater Crested Tern

Greater Crested Tern (Thalasseus bergii) is a large tern with dark grey upperparts, white forehead, shaggy black crest and a long greenish-yellow bill. 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 nests densely on tropical coasts and islands and plunge-dives for fish, sometimes following fishing vessels for discarded catch. 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).