Leach's Storm-Petrel

How to find it

Look far offshore over the Pacific, since it is rare near the coast. Day trips and the Puntarenas-Paquera ferry mostly show other storm-petrels, and the ferry's usual species are Black, Least and Wedge-rumped. A long offshore boat trip is the realistic way to look for Leach's. Long-range trips run from the Cabuya and Cabo Blanco area of the Nicoya Peninsula and from Bahía Herradura, where birders are developing sea birding. Scan the open water for that low, bounding flight rather than waiting for one to follow the boat.

How to recognise it

Leach's is a medium-sized, slim seabird, about 20 cm long.

Look for these marks:

Long wings.

A deeply forked tail.

Mostly blackish brown plumage.

A pale grey band across the upper wing. That pale diagonal bar is a good mark to photograph.

Compared with Wilson's Storm-Petrel, it is larger, with longer, more angular wings and a longer, forked tail. Do not rely on a white rump alone, because birds with a pale rump and birds with a dark rump both occur in Costa Rican waters. Where the rump is white, a dark line splits it, though that line can be hard to see at a distance.

What it sounds like

Recording: Sean Vanderluit, CC BY 4.0, source, read 4 Nov 2026.

Behaviour and diet

The flight is the best clue. It is compared to that of a nighthawk, and over the water it flies low, with erratic, bounding wingbeats. It is more bounding and less fluttery than Wilson's Storm-Petrel.

It patters on the water and picks small planktonic food from the surface. It spends most of the year far out at sea and comes ashore at night only to breed. Unlike Wilson's Storm-Petrel, it seldom follows ships.

Where it lives

Leach's lives over the open ocean and nests on islands in the north. It is known mainly as a bird of the open sea, not the coast.

In Costa Rica it is a Pacific bird, uncommon to fairly common far offshore and rare close to shore or in the Gulf of Nicoya. It has not been recorded at sea off the Caribbean coast, though a stray white-rumped bird there would not be a surprise.

When to see it

In the Gulf of Nicoya and near the coast, records fall mainly between May and August, and these are non-breeding birds.

Similar birds

The deeply forked tail separates Leach's from the Band-rumped Storm-Petrel, which has a square tail. Both are on the Costa Rican list. The dark-rumped Pacific form can be mistaken for at least three other all-dark storm-petrel species, so watch the wingbeats and the overall colour. Against Wilson's, look for the larger size and longer angular wings.

Names and lore in Costa Rica

The official Spanish name in Costa Rica is Paiño de Leach. Some Costa Rican name lists also give Paiño Boreal, the name used more widely in Spanish.

Status and conservation

The AOCR list classes it as M, a migrant, and it is a regular visitor off the Pacific coast.

Photography tips

The pale diagonal bar across the upper wing is a good mark to photograph. The dark line splitting the white rump can be hard to see at a distance, so do not count on it in your images.