- Gelochelidon nilotica
Length 33–43 cm (13-17 in), wingspan 85-103 cm, weight 130-300 g.
A stocky, but long-legged, gull-like tern with a stout, all-black bill, black cap in summer (reduced to a small black ear patch in winter); tail only shallowly forked. Upperparts, including rump and tail, pale silvery-grey (tips of primaries darker), underparts white, legs black. In flight, broad-winged, reminiscent of a small gull or a large marsh tern. Juvenile with buffy-brown to blackish 'V'-marks above, otherwise similar to adult winter.
- 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.
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, Australia and New Zealand. Migratory in the temperate Northern Hemisphere, wintering south to the tropics; resident or dispersive in the subtropics and the temperate Southern Hemisphere.
An annual vagrant in the British Isles, mostly to the south coast.
Six subspecies are recognised; differences between them slight, involving overall size and bill size:
- G. n. nilotica:
- G. n. addenda:
- G. n. macrotarsa:
- Australia (except arid areas); the largest subspecies
- G. n. aranea:
- G. n. vanrossemi:
- G. n. gronvoldi:
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).
The diet consists mostly of large insects, but also feeds on frogs and small mammals.
Breeds colonially in a variety of habitats: lakes, fresh and saline marshes. Also mountain lakes to a height of around 2000m.
- Clements, J. F., T. S. Schulenberg, M. J. Iliff, S. M. Billerman, T. A. Fredericks, B. L. Sullivan, and C. L. Wood. 2019. The eBird/Clements Checklist of Birds of the World: v2019. Downloaded from http://www.birds.cornell.edu/clementschecklist/download/
- Collins Pocket Guide to British Birds 1966
- Collins Field Guide 5th Edition
- Collins Bird Guide ISBN 0 00 219728 6
- BirdForum Opus contributors. (2021) Gull-billed Tern. In: BirdForum, the forum for wild birds and birding. Retrieved 27 January 2021 from https://www.birdforum.net/wiki/Gull-billed_Tern