The orange-billed terns provide an exciting identification challenge. Out-of-range individuals may be very difficult to identify. We need more information on variation within and among the taxa. Various hybrids may also obscure the pattern of extreme vagrants such as Elegant Terns in Europe. In this section we will deal with the “Thalasseus” terns : Crested Tern, Royal Tern, Lesser Crested Tern, Chinese Crested Tern, Elegant Tern, Cayenne Tern and Sandwich Tern.