Bridled Tern (Sterna anaethetus)

Taxonomy

At least 6 subspecies:
S. a. melanoptera - Atlantic coast of Africa.
S. a. fuligula - Red Sea, Persian Gulf, Arabia to western India. S. a. antarctica - eastern Africa, Madagascar, Seychelles, Mascarenes to Andaman Is.
S. a. anaethetus - southern Japan, Taiwan, Philippines, Indonesia to Australia.
S. a. nelsoni - western Mexico and Central America.
S. a. recognita - West Indies.

Also known as Brown-winged Tern.



Figures 1 and 2. Bridled Terns like to rest on surface debris such as pieces of wood or fishing floats. Photograph taken in the Gulf Stream off North Carolina in August. Photograph copyright of Angus Wilson©.
 

Identification

Very similar to Sooty Tern. Might also be confused with Aleutian Tern. Bridled Tern is about the size of a Common Tern but appears slightly longer winged and heavier in flight. Separation from Sooty Tern requires good views (supplemented with field experience of both species). One very useful difference between adult Bridled and Sooty Terns is the shape of the white forhead patch: in Bridled Tern, the white extends back over the eye (like a supercilium) while in Sooty Tern the white just reaches the eye. The black loral stripe is narrower in Bridled Tern and reaches the base of the upper mandible rather than the gape.


Figure 3. In flight. Off North Carolina in August. Photograph copyright of Angus Wilson©.

The mantle is paler than that of Sooty Tern and in good light there is a visible contrast between the black cap and gray nape and back. Adult winter and first winter birds show extensive white mottling on the crown. While the supercilium is still evident, the loral stripe can be much reduced.

Compared to adults, juveniles have pale feather edging to the upperparts. The outer tail feathers have whitish tips, contrasting with the completely white outer tail feathers of adults. Note that the number of white outer tail feathers differs between subspecies. Unlike juvenile Sooty Terns, the underparts of juvenile Bridled Terns are white.

Can be vocal at sea, especially when actively feeding. Utters a variety of short, harsh calls. Often encountered well offshore feeding in small groups on surface fish (most less than 6 cm long) associated with current lines, sargassum patches and floating debris. Picks fish from the surface by making shallow dives (up to 1 m) or by hovering.
 

Where and When

Not globally threatened. Population estimated at more than 200,000 pairs. Movements between breeding and non-breeding grounds poorly understood. More details of European records can be found here.
 

Photographs on the web


Figure 4. In flight, showing the darker trailing edge to the underwing. Sooty Terns show a more uniformly dark undering hand. Taken off North Carolina in August. Photograph copyright of Angus Wilson©.
 

Literature

Marantz, C. A., & A. W. Kratter. (1998) Unusual bird observations near Baton Rouge [LA] associated with Hurricane Andrew, with notes on identification of adult Bridled and Sooty Terns. J. Louisiana Ornithol. 4: 17-24.



Copyright © 2002 All rights reserved. Angus Wilson
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