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Caspian Tern | Hydroprogne caspia
Reuzenstern | Pagaza piquirroja
The Caspian Tern is the largest tern in the world, with a build closer to that of a gull. It breeds across five continents. In the guide area it breeds locally in northwestern Mexico; elsewhere it is a winter visitor and passage migrant from North America that becomes scarcer to the south.
Voice
A deep, raw, heron-like kraa-ah or kreeeh-ap, lower than any other tern. Juveniles following their parents give a high, whistled wheeoo.
Recording: Clément Bruneau — CC BY-NC-SA 4.0 · converted to mono · xeno-canto
Identification
48–60 cm, heavily built, with broad wings, a short, shallowly forked tail and a very thick, deep red bill with a dark smudge near the tip. In breeding plumage the cap is entirely black and without a crest; outside the breeding season the forehead is finely streaked white and the cap mottled blackish-grey, but never as white as in Royal Tern. Upperparts are pale grey, underparts white. In flight the dark grey tips of the primaries form an obvious dark patch from below. The legs are black. Juveniles have an orange-red bill, a brown-spotted back and a dark cap.
Confusion species
Royal Tern Thalasseus maximus is slightly smaller and slimmer, with a thinner orange bill, a short crest and, outside the breeding season, a white forehead with black confined to the hindcrown; from below the primaries are mostly pale. Gull-billed Tern Gelochelidon nilotica is much smaller, with a short black bill. At a distance the bulky shape may suggest a gull, but gulls lack the red dagger bill and do not dive.
Habitat
Sheltered coastal waters: lagoons, estuaries, salt pans, shallow bays and mudflats, as well as large lakes and reservoirs inland. It hunts by patrolling high above the water with the bill pointed down, then plunging steeply; the diet is mainly fish. It roosts on sandbars, beaches and quays, often among Royal Terns and gulls. It breeds in colonies on bare sandy or shelly islets.
Where the bird is most at home, classified by the vegetation units of Mexico and Central America.
Range and movements
Breeds locally in colonies along the Pacific coast of Baja California and in the Gulf of California. Outside the breeding season along both coasts of Mexico, fairly common in the north and scarcer southwards; in Central America a scarce winter visitor south to Panama, mainly on the Pacific side. Outside the guide area the species breeds in North America, Europe, Asia, Africa and Australia; North American birds winter from the southern United States to northern South America.
- 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
Lagoons, salt pans and estuaries in northwestern Mexico offer the best chance, especially in winter. In resting flocks of terns it stands out by its thick red bill and dark cap; in flight the dark underside of the primaries is the best feature. The low, raw call is often heard before the bird comes into view.
Conservation status
Not threatened. The world population is large and has increased in North America in recent decades, although large colonies are vulnerable to disturbance, flooding and conflicts with fisheries.
Scientific name
Hydroprogne caspia | (Pallas, 1770)
Pallas described the species in 1770 as Sterna caspia; because it was later moved to another genus, the author and year stand in brackets. The genus Hydroprogne was introduced in 1829 by Kaup. Hydroprogne joins Greek hudro- 'water' to Latin progne 'swallow'. caspia is Latin and refers, like the English name, to the Caspian Sea. The specimen the first description was based on came from Caspian Sea.