Spectacled tern Spectacled tern The spectacled tern ("Onychoprion lunatus"), also known as the grey-backed tern, is a seabird in the family Laridae. A close relative of the bridled and sooty terns (with which it is sometimes confused), the spectacled tern is less common than the other members of its genus and it has been studied less. The three species, along with the Aleutian tern were recently split into a new genus "Onychoprion" from "Sterna" (Bridge "et al.", 2005). They resemble the sooty tern but with a grey back instead of a black one. Their breast and underparts are white, and they have
Royal tern adult royal tern has an average wingspan of , for both sexes, but their wingspan can range from . The royal tern's length ranges from and their average weight is anywhere from . The calls of the royal tern are usually short, clear shrills. Some of the shrills sound like "kree" or "tsirr"; the royal tern also has a more plover like whistle that is longer, rolling and is more melodious. In various parts of its range, the royal tern could be confused with the elegant tern, lesser crested tern (the other orange-billed terns), and the greater crested tern. It