Bridled tern  (Sterna anaethetus)

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

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

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

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).

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).

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).

Environment Agency - Abu Dhabi is a principal sponsor of ARKive. EAD is working to protect and conserve the environment as well as promoting sustainable development in the Emirate of Abu Dhabi.

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

To find out more about the bridled tern and its conservation see:

• The Birds of North America Online:
  http://bna.birds.cornell.edu/bna/species/468/articles/introduction

For more information on this and other bird species please see:

• BirdLife International:
  http://www.birdlife.org