Bridled tern (Sterna anaethetus)

Bridled tern in flight
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Bridled tern fact file

Bridled tern description

GenusSterna (1)

The specific name of the bridled tern, anathetus, is derived from the Greek for senseless or stupid, a reference to the ease with which hungry sailors captured this relatively docile seabird (3). Relative to other terns, the bridled tern is of average size, with a deeply-forked tail and long narrow wings. During the breeding season, the upperparts of its plumage, including the back, wings and tail, are brownish grey, while the underparts are generally whitish. The crown and nape are black but the forehead is marked by a triangular white patch that extends above and behind the eyes. The bill is about as long as the head and is black in colour, as are the legs and feet. Outside of the breeding season, the bridled tern is slightly paler, with its black crown streaked white and brown, and the dark feathers of the upperparts having white-tips, giving it a peppered appearance. Juveniles are similar in appearance to the adults but have a paler, streaked crown and upperparts heavily scaled with white and buff. Four to six subspecies, differing only slightly in appearance but occupying different parts of the bridled tern’s overall range, are variably recognised (2) (3).

Onychoprion anaethetus.
Sterne bridée.
Length: 35- 38 cm (2)
95 - 150 g (2)

Bridled tern biology

The seasonal movements of the bridled tern are not well known, but most populations abandon the breeding sites in loose flocks at the end of the breeding season to overwinter at sea. During this time, the bridled tern typically associates with large patches of macroalgae and general flotsam, which it uses as a floating perch (2) (3) (4). It feeds mainly on surface-schooling fish, which it catches by diving head first into the water, or by swooping low over the sea to collect prey from the surface. As an alternative it will rest on the surface and catch fish merely by dipping its head or bill into the water (2). Aside from fish, the bridled tern also takes small amounts of squid and crustaceans, and occasionally aquatic insects (2) (4).

The timing of the breeding season varies geographically, but most populations breed in small groups ranging in size from 2 to 30 pairs, but sometimes comprising several hundred (2) (4). The nests are often distributed in vegetation, rock or rubble, where they can be concealed to reduce the chances of predation. Each breeding pair produces just a single egg which is incubated for 28 to 30 days before hatching. The young fledge when around 50 to 65 days old, but remain dependent on the parent birds for another 30 to 35 days (2).


Bridled tern range

A large distribution encompassing tropical and subtropical coasts of the Atlantic, Indian and western Pacific Oceans (2) (3) (4).


Bridled tern habitat

The bridled tern breeds on coral, rock, or sandy shorelines, and forages over inshore waters and up to 50 kilometres offshore (2) (4).


Bridled tern status

Classified as Least Concern (LC) on the IUCN Red List (1).

IUCN Red List species status – Least Concern


Bridled tern threats

Although the bridled tern is not globally threatened (2), it is extremely vulnerable to oil spills and is known to respond poorly to severe human disturbance and the introduction of domestic cats at breeding sites (4).


Bridled tern conservation

The focus of conservation efforts is to protect vulnerable bridled tern nesting colonies through barriers and signs, the education and supervision of visitors, and to habituate the species to the presence of humans at sites exposed to long term visitation (4).

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View information on this species at the UNEP World Conservation Monitoring Centre.

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The act of keeping eggs warm so that development is possible.
Specific name
The second name in the binomial nomenclature system that distinguishes a species from other species of the same genus.
A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.


  1. IUCN Red List (January, 2009)
  2. del Hoyo, J., Elliott, A. and Sargatal, J. (1996) Handbook of the Birds of the World. Volume 3: Hoatzin to Auks. Lynx Edicions, Barcelona.
  3. Haney, C.J., Lee, D.S. and Morris, R.D. (1999) Bridled Tern (Sterna anaethetus), The Birds of North America Online. Cornell Lab of Ornithology, Ithaca. Available at:
  4. BirdLife International (July, 2009)

Image credit

Bridled tern in flight  
Bridled tern in flight

© Don Hadden /

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