About Onychoprion anaethetus (Scopoli, 1786)
Onychoprion anaethetus (Scopoli, 1786), commonly known as the bridled tern, is a medium-sized tern. It measures 30–32 cm in length with a 77–81 cm wingspan, a size similar to the common tern, but has a heavier build. It has long wings, a deeply forked tail, dark grey upperparts, and white underparts. Its forehead, eyebrows, and a distinct collar on the hindneck are all white, and it has black legs and a black bill. Juvenile bridled terns have scaly grey plumage on their upperparts and pale plumage on their underparts. This species is unlikely to be confused with most other terns, with only two exceptions: the similarly dark-backed sooty tern, and the spectacled tern native to the Tropical Pacific. Compared to the sooty tern, the bridled tern has paler upperparts (though it is not as pale as the grey-backed tern), a narrower white forehead patch, and a pale neck collar. The bridled tern is a migratory and dispersive bird that winters across a broader range of tropical oceans. Compared to most other tern species, it has strongly marine habits. The Atlantic subspecies O. a. melanopterus breeds in Mexico, the Caribbean, and west Africa. Other recognized subspecies occur around the Arabian Peninsula, in Southeast Asia, and in Australasia, but the exact number of valid subspecies for this species is disputed. The International Ornithological Congress (IOC) recognizes four distinct subspecies: O. a. melanopterus (Swainson, 1837), found in the Caribbean and West Africa; O. a. antarcticus (Lesson, 1831), found in the Red Sea, Persian Gulf, and western Indian Ocean; O. a. anaethetus (Scopoli, 1786), found in the eastern Indian Ocean and Pacific Oceans; and O. a. nelsoni (Ridgway, 1919), found along the west coast of Mexico and Central America. The bridled tern is a rare vagrant to western Europe.
