All species › Waders, gulls and terns › Skimmers, noddies, terns and gulls › Bridled Tern
Bridled Tern | Onychoprion anaethetus
Brilstern | Charrán embridado
The Bridled Tern is the smallest and slenderest of the dark sea terns of this genus, and the only one that willingly drops onto whatever happens to be floating: a buoy, a coconut, a raft of sargassum weed or the back of a basking sea turtle. It breeds on rocky islets around the Caribbean and the Gulf of Mexico, always under cover, and in summer it is the commonest dark tern of the Gulf Stream.
Voice
At the colony it gives a low, hoarse, barking wep-wep, alongside a growling rasp that comes out of crevices under boulders where the birds have their nests. The tone is clearly lower and rougher than the shrill screaming of the Sooty Tern. At sea it is nearly silent; over a productive patch it gives short sharp cries. Because it breeds scattered and in small groups, a Bridled Tern colony is never the wall of sound that a Sooty Tern colony is.
Recording: David Darrell-Lambert — CC BY-NC-SA 4.0 · Jana Island, Saudi Arabia · xeno-canto
Identification
A slender tern with long wings and a long, deeply forked tail with white outer edges. The upperparts are brownish grey, clearly paler than a Sooty Tern's, and a pale collar sits between the black cap and the grey mantle. The white forehead patch runs on as a narrow eyebrow behind the eye, with a black loral line below it — the 'bridle' of the name. The underparts are white and the underwing largely white with a dark trailing edge; bill and legs are black. Male and female are alike. Young birds have a shorter tail, pale fringes on the mantle and a dark head heavily speckled with white.
Confusion species
Sooty Tern (Onychoprion fuscatus) is larger, black rather than grey on the back, lacks the pale collar and has a white forehead patch that stops above the eye. Gray-backed Tern (Onychoprion lunatus) of the Pacific is even more similar, but is larger and darker grey and also has no collar; in the Atlantic it does not occur. Young Sooty Terns are entirely dark and much darker than any Bridled Tern. Behaviour helps too: the Bridled Tern flies more loosely and more erratically, stays closer to land and does settle on floating objects — something the Sooty Tern seldom does.
Compare terns: bill, legs, head and tail side by side
Habitat
It feeds over warm seas, usually within a few tens of kilometres of land and with a marked preference for the edges of drifting sargassum mats, where small fish and shrimps shelter. It dives shallowly or picks from the surface while hovering, swooping down from three to ten metres up. It breeds in loose colonies on rocky islets, and always under cover: beneath an overhanging rock, deep in a crevice, or under a bush. That hidden nest site is the clearest division from the Sooty Tern, which nests on open sand. The deep, empty ocean far from any island it uses less than its black counterpart.
Where the bird is most often found, arranged by the USNVC — the vegetation classification of the United States and Canada — and CMECS for sea and coast.
Range and movements
The range is pantropical, with four subspecies. In this region birds of the Atlantic form breed on cays and rock islets of the Bahamas, Cuba, Hispaniola, Puerto Rico, the Cayman Islands, the islands off Yucatán and the coast of Belize and Honduras, and further south on Aruba and Curaçao; on the Pacific side another form breeds on the islands off western Mexico. In the contiguous United States it has been confirmed breeding only since 1987, in the Florida Keys, and since 2005 also on Bush Key in the Dry Tortugas; a handful of pairs are involved. From May to September it is numerous in the Gulf Stream off Florida and the Carolinas and over the deeper parts of the Gulf of Mexico. Outside those months it withdraws to tropical waters and is virtually absent inshore.
- Breeding (summer)
- Winter
- Passage
- dark = core range, pale = thinly spread
Where and when to look
The best chance in the United States is a pelagic trip from Hatteras or Oregon Inlet in North Carolina, from late May to early September: along a line of drifting sargassum it often sits on the weed itself or on a piece of driftwood. Work such a line slowly and look for perched birds — a dark tern resting on something floating is nearly always a Bridled Tern and hardly ever a Sooty. Then check the pale collar on the hindneck, the mark that holds up even in poor light.
Conservation
The world population is put at four hundred thousand to a million mature birds and the species is listed as of Least Concern (LC). Introduced rats and cats on breeding islands and the taking of eggs are a local problem. Because the nests lie deep under rocks and bushes, colonies are hard to count and the trends remain uncertain. In the Caribbean breeding islets are being lost to coastal erosion, severe storms and tourism.
Scientific name
Onychoprion anaethetus | (Scopoli, 1786)
Giovanni Antonio Scopoli described the species in 1786 as Sterna anaethetus; because it has since changed genus, author and year stand in parentheses. The genus Onychoprion is formed from Greek onyx 'claw' and prion 'saw'. anaethetus goes back to Greek anaisthetos, 'senseless, foolish', after the tameness with which breeding seabirds allow an approach. Scopoli gave the locality as 'in Guinea', but the specimen came by way of Sonnerat from the Philippines and had in fact been collected on Panay.