 The greater crested tern has grey upperparts , white underparts , a yellow bill , and a shaggy black crest that recedes in winter . Its young have a distinctive appearance , with strongly patterned grey , brown and white plumage , and rely on their parents for food for several months after they have fledged . Like all members of the genus Thalasseus , the greater crested tern feeds by plunge diving for fish , usually in marine environments ; the male offers fish to the female as part of the courtship ritual . 
