Wedge-rumped Storm-Petrel

How to find it

Start at the tip of Puntarenas, the most accessible shore spot for seabirds, where storm-petrels feed where the two waters of the gulf converge. Even so, a local birder rarely saw it from shore, so a boat gives better odds. On the water, scan for small, fast-flying birds away from the big flocks of Black Terns and Galapagos Shearwaters. Guides at Manuel Antonio say seabirds are hard to identify because of distance, fast motion and the moving ship. Take your time and let your guide call the rump pattern.

How to recognise it

This is a very small, dark storm-petrel. Look for these marks:

A long white rump patch that looks as if it covers most of the tail.

White reaching nearly to the tip of the slightly forked tail.

White tail sides and white undertail coverts.

Dusky plumage overall, with pale bars on the upper wings.

Fairly deep wingbeats.

Short legs that do not reach past the tail in flight.

Rump and undertail pattern matter a great deal in this group. On a Costa Rican pelagic trip, one birder had trouble separating white-rumped storm-petrels. He suspected that a bird lacking the white wedge and white undertail was a Leach's or Band-rumped.

Behaviour and diet

It feeds by skipping over the sea surface and pattering on the water. It usually flies low over the surface and takes small fish, squid and crustaceans. It often looks as if it is dancing while it feeds, which fits the name Danzarin.

Boat birders look for small, fast-flying storm-petrels away from the big flocks of Black Terns and Galapagos Shearwaters. A Wedge-rumped once came right up beside the boat. Dolphin pods on outings from Cabuya drew large flocks of seabirds.

Where it lives

This is a bird of the open ocean. It nests in rock crevices on islands and sea cliffs, not in Costa Rica. Here it is a non-breeding visitor offshore.

Off Costa Rica and Panama the Peruvian race tends to stay within about 100 km of land, while the Galápagos race ranges farther out to sea. Away from the nesting season, most birds spread out along the Humboldt Current. Records come from the Gulf of Nicoya, the tip of the Nicoya Peninsula and the central and south Pacific off Manuel Antonio.

When to see it

Off Costa Rica and Panama, the Peruvian race is usually recorded from May to November. Rainy season is described as a good time in the Gulf of Nicoya, because nutrients wash into the gulf.

Similar birds

Wilson's Storm-Petrel is the closest lookalike. Its rump white is less extensive, and it has yellow on the feet if seen well. Black Storm-Petrel is all dark and skims low over the waves like a shadowy nighthawk. Least Storm-Petrel is also uniformly dark with no white rump, and is easy to recognise in Costa Rica by its bat-like flight.

Names and lore in Costa Rica

The Spanish name on the Costa Rican official list is Paiño Danzarin. Other Spanish names used for the species elsewhere include Paiño de las Galápagos and Golondrina de mar peruana.

Status and conservation

Costa Rica's official list (AOCR) marks it as a migrant (M), and the IUCN rates the species Least Concern.