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Bridled tern
Onychoprion anaethetus | Brilstern | Charrán embridado
The warm-water counterpart of the Sooty Tern, but a bird of the shelf rather than the deep ocean: it feeds along current lines, over reefs and around rafts of floating weed. The name refers to the narrow white brow that runs back past the eye like the strap of a bridle.
Voice
A yapping, high wep-wep and a hoarse kerr, given at the colony and by parties feeding together. The call is shorter and higher than the Sooty Tern's wide-awake, and vagrants are almost always silent.
No freely licensed recording is available for this species yet.
Identification
A medium-sized, slender tern with grey-brown upperparts distinctly paler than the black cap. A narrow white brow starts in front of the eye and continues behind it, and a white collar separates cap from mantle. The underparts are white with a grey wash, the tail is deeply forked with long white outer feathers, and the bill and legs are black. Juveniles are paler and more finely scaled than young Sooty Terns, with a pale head and a dark line through the eye.
Confusion species
Sooty Tern is the comparison that matters. Bridled has a grey-brown back, Sooty a black one, and against the light at sea that contrast can vanish, at which point the head decides. The white forehead of Bridled is narrow and carries on behind the eye as a brow; on Sooty it is broader and stops at the eye. Only Bridled shows a white collar between cap and mantle, and its outer tail feathers are longer and whiter. Set against Arctic Tern on a seawatch, Arctic is pale grey above with a translucent hand and a red bill, while Bridled is dark above, white below and black-billed and flies on slower, deeper beats with a longer tail.
Habitat
Warm seas over the continental shelf, along current lines and over reefs, where the birds pick small fish, squid and shrimps from the surface. They perch readily on driftwood, buoys and weed rafts, which is unusual in a tern. Nests are hidden under boulders, in rock crevices and beneath low scrub on rocky islets.
Where the bird is most at home, classified with EUNIS — the European standard for habitats.
Range and movements
Breeds in the Red Sea, the Persian Gulf, the Caribbean, off West Africa and through the Indian and Pacific Oceans. In Europe it amounts to a handful of records a decade, mostly in summer, along Atlantic coasts and in the western Mediterranean, and individual birds have lingered for weeks at seabird colonies in north-west Europe.
- Breeding (summer)
- Passage
- dark = core range, pale = thinly spread
Where and when to look
Seawatching in July and August after a spell of southerly winds gives the best odds. Check tern flocks on groynes and sandbanks for a bird that is dark above with a narrow white brow and long white outer tail feathers, and remember that Bridled Tern will settle on floating objects offshore where other terns keep flying.
Conservation status
Not globally threatened. Colonies are nonetheless sensitive to introduced rats and cats, to disturbance from boat traffic around small islands and to egg collecting, and coastal development is removing nesting sites in the Red Sea and the Gulf.