Yellow-billed Tern

How to find it

Begin with a slow boat trip on the Río Frío at Caño Negro with local guides, since Costa Rica's first accepted bird was found in this wetland. Scan mudflats and lagoon edges where waterbirds gather, because the photographed birds were perched among other waterbirds or resting with sandpipers. Look up as well, since one was seen hovering above the wetland. The lagoons and rice areas of the Caño Negro and Tempisque lowlands are the wetland types worth scanning. Photos from local birders are how Costa Rica finds vagrant terns like this one, so a camera helps. Treat any sighting as a bonus.

How to recognise it

Start with size and colour: this is a very small tern with a yellow bill and yellow legs.

The adult shows:

- a black cap

- a short white V on the forehead

- a gray back

- white underparts

Non-breeding birds, across the species' range, have a mostly white head with dark streaks on the nape and around the eyes, and the yellow bill has a dusky tip. The bird photographed at Caño Negro and the one at Camaronera Tempisque were both in non-breeding plumage, so that paler look is the one to expect here.

In flight, look for a broader black wedge on the upper wing, made by 4 to 5 black outer primaries. The tail is shorter and less forked than that of the Least Tern, and the bill carries no black tip.

What it sounds like

Recording: Eduardo Luis Beltrocco, CC BY 4.0, source, read 4 Nov 2026.

Behaviour and diet

The Yellow-billed Tern feeds in daylight on small fish, shrimp and insects. It hovers and picks prey from the water surface, and it often hovers before it dives for fish.

A photographer at Caño Negro saw one hovering 10 to 15 m above a wetland, then dropping to a mudflat to perch among other waterbirds at dusk. At Camaronera Tempisque in Guanacaste, another was resting with sandpipers.

Range-wide, it often nests next to colonies of Large-billed Terns and Black Skimmers on sand banks.

Where it lives

Across South America this tern lives on rivers, swamps and freshwater lakes, and it is usually found below 500 m elevation. Outside the breeding season it uses coastal lagoons, river mouths and rice fields.

In Costa Rica the records come from lowland wetlands: Laguna de San Sebastián in Caño Negro, in the north; Camaronera Tempisque in Cañas, Guanacaste; and Ciudad Neily, Puntarenas, in the far south, where a nest was documented in February 2016.

When to see it

Caño Negro's wetland birding is described as best in the dry season, February to April, when falling water levels crowd the birds together. That applies to the refuge in general, not to this tern in particular.

Similar birds

The Least Tern (Charrán Chico) is a migrant on the Costa Rican list and the closest lookalike. It is more often found on the coast. The Yellow-billed Tern has a heavier bill with no black tip and a shorter, less forked tail, and in flight the Least Tern has only 2 black outer primaries against 4 to 5. The Large-billed Tern (Charrán Picudo) is also accidental here, but it is much larger.

Names and lore in Costa Rica

Costa Ricans use the name Charrán Piquiamarillo. Elsewhere in South America it is called Gaviotín de Río, Gaviotín chico, Charrancito Amazónico, Gaviotín Fluvial (Colombia) or Gaviotín Amazónico (Ecuador).

Status and conservation

The AOCR list, updated June 2026, gives it the status A, accidental, with uncertain residency.

Photography tips

Perched birds were photographed among other waterbirds on mudflats at dusk and resting with sandpipers, so check loafing flocks at the water's edge. A hovering bird was seen 10 to 15 m above the wetland, so keep a lens ready for that moment. Small terns are hard to separate: a Ciudad Neily birder studying photos of a small tern could not fully rule out Yellow-billed Tern, so take several clear frames.