Similar Elegant tern, Cabot's tern, Lesser crested tern, Thalasseus, Royal tern | ||
Orange-billed tern is a name applied to a group of three large terns in the genus Thalasseus with orange bills, which are quite similar in appearance and often considered difficult to identify, namely:
The greater crested tern (Thalasseus bergii) and the Cayenne tern (Thalasseus sandvicensis eurygnatha), which have yellow rather than orange bills, are sometimes also considered part of this group.
Identification
Identification of orange-billed terns within their range is straightforward. Crested and Cayenne terns (which do not overlap in range) can be identified by their bill colour. Of the truly orange-billed species, the only geographical overlaps are between royal and lesser crested, and between royal and elegant Terns, and in both cases the larger size and strong bill of royal tern should prevent misidentifications (in addition, lesser crested terns have a grey, not white, rump).
Identification of vagrants has proved to be much more difficult however, with known hybridisation, and birds which do not match the classic character sets of individual species. See the references list below for more information.