Orange-billed tern
Encyclopedia
Orange-billed tern is a name applied to a group of three large tern
Tern
Terns are seabirds in the family Sternidae, previously considered a subfamily of the gull family Laridae . They form a lineage with the gulls and skimmers which in turn is related to skuas and auks...

s in the genus Thalasseus
Thalasseus
Thalasseus, the crested terns, is a genus of six species of seabirds in the tern family. Thalasseus signifies a "creature of the sea". It has a worldwide distribution, and many of its species are abundant and well-known birds in their ranges...

with orange bills, which are quite similar in appearance and often considered difficult to identify, namely:
  • Royal Tern
    Royal Tern
    The Royal Tern is a seabird in the tern family Sternidae. This bird has two distinctive subspecies. T. m. maximus breeds on the Atlantic and Pacific coasts of the southern USA and Mexico into the Caribbean. The slightly smaller T. m. albididorsalis breeds in coastal west Africa...

    , Thalasseus maximus
  • Lesser Crested Tern
    Lesser Crested Tern
    The Lesser Crested Tern is a seabird of the tern family Sternidae...

    , Thalasseus bengalensis
  • Elegant Tern
    Elegant Tern
    The Elegant Tern is a seabird of the tern family Sternidae. It breeds on the Pacific coasts of the southern USA and Mexico and winters south to Peru, Ecuador and Chile....

    , Thalasseus elegans


The Greater Crested Tern
Greater Crested Tern
The Greater Crested Tern , also called Crested Tern or Swift Tern, is a seabird in the tern family which nests in dense colonies on coastlines and islands in the tropical and subtropical Old World...

 (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.
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