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Gull-billed Tern | Gelochelidon nilotica
Lachstern | Pagaza piconegra
The Gull-billed Tern often behaves like a gull: it rarely dives, but picks its food from the water or the ground in flight and hunts a lot over land. Crabs, insects, lizards and small fish are on the menu. In the guide area it breeds locally in Mexico and is otherwise a winter visitor along both coasts south to Panama. The subspecies vanrossemi lives on the Pacific side, aranea on the Atlantic side.
Voice
A nasal, rather hoarse ker-wik or kay-wek, often repeated in flight; at the colony also a harsh kraak.
Recording: Walter Wallner — CC BY-NC-SA 4.0 · converted to mono · xeno-canto
Identification
33–42 cm, stocky for a tern, with broad wings, a short, shallowly forked tail and long black legs. The key feature is the short, thick, all-black bill, more like a gull's than that of other terns. In breeding plumage the cap is entirely black; in non-breeding plumage the head is white with a dark patch behind the eye. The upperparts are very pale silvery grey, the rump and tail grey too. In flight a narrow dark trailing edge to the wingtip. Juveniles have a pale brown wash on the crown and back and a dark eye patch.
Confusion species
Sandwich Tern Thalasseus sandvicensis is slimmer, with a longer, thin black bill with a yellow tip, a shaggy crest and shorter legs. Forster's Tern Sterna forsteri also has a dark eye patch in non-breeding plumage, but is smaller, with a thin bill, a longer, deeply forked tail and orange legs. Caspian Tern Hydroprogne caspia is much larger and has a thick red bill.
Habitat
Lagoons, salt pans, mudflats, coastal marshes, rice fields, wet pastures and beaches; more often over land and shallow water than over open sea. It flies low and unhurried back and forth and swoops down at an angle to pick prey from the surface or the ground. It breeds in small colonies on bare sandbars and islets in lagoons, with a shallow scrape as a nest.
Where the bird is most at home, classified by the vegetation units of Mexico and Central America.
Range and movements
Breeds locally along the Gulf of California and the Pacific coast of northwestern Mexico, and along the Gulf of Mexico, including the Yucatán Peninsula. Outside the breeding season along both coasts of Mexico and Central America south to Panama, most numerous on the Pacific side, and also at inland waters in the lowlands. Outside the guide area the species breeds along the coasts of the United States, locally in South America and in Europe, Africa, Asia and Australia.
- Resident
- Summer visitor (c. Apr–Sep)
- Winter visitor (c. Oct–Mar)
- Passage (Mar–Apr, Oct–Nov)
- dark = core range, pale = thinly spread
How and when to look
Salt pans, shallow lagoons and rice fields in the coastal lowlands are the places to search. A pale tern hunting low over dry ground or a rice field without diving is often a Gull-billed Tern. The short black bill is the decisive feature in every plumage.
Conservation status
Not threatened. Widespread worldwide, but in North America it has declined in many places through loss of breeding sites and disturbance. Colonies on sandbars and islets are vulnerable to flooding, recreation and predation by introduced mammals.
Scientific name
Gelochelidon nilotica | (Gmelin, 1789)
Gmelin described the species in 1789 as Sterna nilotica; because it was later moved to another genus, the author and year stand in brackets. The genus Gelochelidon was introduced in 1830 by Brehm. Gelochelidon is Greek, from gelaō 'to laugh' and khelidōn 'swallow'. nilotica is Latin for 'of the River Nile', after the region the described bird came from. The specimen the first description was based on came from Egypt.