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Gull-billed Tern - BirdForum Opus

(Redirected from Sterna nilotica)
G. n. nilotica : Breeding plumage
Photo © by scottishdude
Goa, India, March 2009
Gelochelidon nilotica

Sterna nilotica

Identification

G. n. nilotica : Non-breeding plumage
Photo © by Alok Tewari
Jamnagar, Coastal Gujarat, India, Jan-2016

Length 33–43 cm (13-17 in), wingspan 80-95 cm.
A stocky but long-legged, gull-like tern with a stout, all-black bill. In flight, broad-winged, reminiscent of a small gull or a large marsh tern.

  • cap black in summer, reduced to a small black ear patch in winter
  • tail only shallowly forked
  • upperparts, including wings, pale silvery-grey
  • tips of primaries dark, generally giving a dark trailing edge
  • rump and tail pale silvery grey
  • underparts white
  • legs black, long

Juvenile with buffy-brown to blackish 'V'-marks above, otherwise similar to winter adult, but smaller.

Variation

European birds average larger and heavier than birds in the Americas.

Similar Species

G. n. nilotica Juvenile
Photo © by AJDH
Al Khobar, Saudi Arabia, July 2006
  • Australian Tern is larger with a larger bill, back and wings very pale with white rather than grey rump and upper tail. Non-breeding: larger black ear coverts which are square-ended.
  • Sandwich Tern has a yellow tip to the black bill, shorter legs, relatively longer, narrower wings in flight, shaggy crest, and white rump and tail; in winter plumage, retains black at rear of head, less so over ear coverts.
  • Whiskered Tern has similar structure, and plumage pattern in winter, but is substantially smaller - though can be hard to tell where size not easily judged - and with slightly more extensive black on rear of head.
  • In winter plumage, Forster's Tern has similar, though more obvious, black ear patches.

Distribution

Like the Caspian Tern, widespread but patchy distributed, breeding in temperate and subtropical regions globally, though not extending so far north as Caspian Tern, in Europe only to 54°N (in northern Germany, though formerly also bred in western Denmark at 56°N), and in North America to 41°N (on Long Island, New York).

Also local in Asia, South America, and as non-breeding in Australia. Migratory in the temperate Northern Hemisphere, wintering south to the tropics; southernmost populations in South America disperse northward even if not too far.

An annual vagrant in the British Isles, mostly to the south coast.

Taxonomy

Adult/G. n. nilotica in flight
Photo © by Kevin Wade
Laguna Salada, Málaga, Spain, April 2018

Australian Tern has been split from this species.

This species was in the past included in the genus Sterna.

Subspecies

Subspecies G. n. Aranea
Photo © by NJLarsen
Pitt Street Causeway, Charleston, South Carolina, 1 May 2023

Morphological differences between races are slight, involving overall size and bill size.

Clements recognises the following subspecies [1]:

Race affinis was formerly called addenda.

Habitat

Breeds on sandy shores of the sea and large lakes, but - uniquely for a tern - feeds mainly over land, typically over coastal marshes and fields. Also overwinters near inland waters (lagoons, marshes, lakes, rivers etc).

Behaviour

Diet

The diet consists mostly of large insects, but also feeds on frogs and small mammals.

Breeding

Breeds colonially in a variety of habitats: lakes, fresh and saline marshes. Also mountain lakes to a height of around 2000m.

References

  1. Clements, J. F., P. C. Rasmussen, T. S. Schulenberg, M. J. Iliff, T. A. Fredericks, J. A. Gerbracht, D. Lepage, A. Spencer, S. M. Billerman, B. L. Sullivan, and C. L. Wood. 2023. The eBird/Clements checklist of Birds of the World: v2023. Downloaded from https://www.birds.cornell.edu/clementschecklist/download/
  2. Gill, F, D Donsker, and P Rasmussen (Eds). 2023. IOC World Bird List (v 13.2). Doi 10.14344/IOC.ML.13.2. http://www.worldbirdnames.org/
  3. Collins Pocket Guide to British Birds 1966
  4. Grant, P.J., K. Mullarney, L. Svensson, D. Zetterstrom (1999) Collins Bird Guide: The Most Complete Field Guide to the Birds of Britain and Europe. Harpercollins Pub Ltd ISBN 0 00 219728 6
  5. Collins Bird Guide ISBN 0 00 219728 6

Recommended Citation

External Links


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