Blue-billed White-Tern

How to find it

Plan around Isla del Coco, since that is where this tern lives and nests in Costa Rica. The island is a remote national park reached by sea. Large seabird colonies nest on the island and on the rocks next to it. Look up into the trees for a white bird on a bare branch, where single eggs sit with no nest. Because pairs return to the same site each year, a known nest tree can be revisited. Its tameness often lets you watch it from close by.

How to recognise it

Adults are all white, and that alone sets this tern apart: it is the only tern with entirely white plumage.

A thin black ring around the eye makes the eyes look huge.

The bill is blue at the base with a black tip, slim and slightly upturned.

The legs are bluish gray and the tail is forked.

The bird is about 30 cm long.

Young birds are less clean. They show a dark spot behind the eye and dark mottling on the nape, and the back and wing coverts have reddish tinges on the feather tips.

What it sounds like

Recording: Eric Knight, CC BY 4.0, source, read 4 Nov 2026.

Behaviour and diet

This tern lays a single egg directly on a bare tree branch, in a fork or small hollow, with no nest at all. In Costa Rica the nests are 5 to 15 m up, sometimes in loose colonies.

Pairs return to the same nest site each year, so a known nest tree can be revisited.

The bird is very tame and lets people come close. Local people also describe it as very delicate and gentle.

Where it lives

This is a bird of the open sea. It usually stays fairly near its nesting islands but sometimes ranges far from them.

In Costa Rica it is tied to Isla del Coco National Park, far out in the Pacific. The park includes Isla del Coco and 8 other islands.

Away from there it is only an occasional or accidental visitor off the Pacific coast, and mainland records are rare.

When to see it

It breeds in large numbers on Isla del Coco from February to September and is absent from the island for the rest of the year. A Costa Rican study gives the breeding season as March to September.

Similar birds

Its pure white plumage is unusual among terns, so confusion is limited. Look for the forked tail and the slim, slightly upturned bill, blue at the base with a black tip. Young birds are less clean white, with the dark eye spot and mottled nape.

Names and lore in Costa Rica

Costa Rican names for this bird include Charrán Blanco Piquiazul, Charrán Blanco and Palomita del Espíritu Santo (little dove of the Holy Spirit). The local name Espíritu Santo (Holy Spirit) comes from how the bird sometimes hovers in place above an observer's head. A Costa Rican seabird article says pirates gave the bird that name.

Status and conservation

The Costa Rican list marks it as a resident (R) that nests in the country, on Isla del Coco, where the park tourism plan calls it a temporary resident.

Photography tips

The bird is very tame and lets people come close, so patience matters more than long lenses. Its single egg sits on a bare branch and pairs return to the same nest site each year, so a known nest tree can be revisited. Watch for birds hovering in place overhead.