Band-rumped Storm-Petrel

How to find it

In Costa Rica it has been found only from boats on the open-ocean crossing to Isla del Coco, not from land. Leach's Storm-Petrel is far commoner on that route, so look carefully through the storm-petrels. Leach's was the most abundant storm-petrel there and was most often seen toward dusk, so check each white-rumped bird against it. The 2020 bird flew very low over the water around the boat, so keep watching the water close to the hull.

How to recognise it

This is a small storm-petrel, about 18 to 20 cm long. Look for these marks, which describe the species in general:

Blackish brown plumage overall.

A narrow, sharply edged white band across the rump, with the white reaching slightly onto the sides of the undertail.

A tail only slightly notched, which can look nearly square. Most other storm-petrels in its subfamily have a more deeply notched tail.

The white rump patch is shared with several other storm-petrels, so identification from a boat is hard and views over moving water are often brief.

Behaviour and diet

It is an ocean-going bird that feeds on small crustaceans, fish and squid, picking prey from the water surface. It spends the non-breeding period at sea. It flies low over the waves with quick, shallow wingbeats and long glides on stiff, slightly bowed wings, a glide birders compare to a small shearwater. At breeding sites it comes ashore only at night and may stay away on bright moonlit nights. It nests in colonies near the sea, in rock crevices, caves or under rocks, and each pair lays a single whitish egg. These are range-wide habits, not Costa Rican nesting records.

Where it lives

In Costa Rica this is a bird of open ocean waters, recorded on the boat route to Isla del Coco in the Pacific. Seabird presence and distribution here are poorly studied, with survey effort mostly along the coasts and in records from Isla del Coco National Park. Range wide, some populations breed on Cocos Island, which belongs to Costa Rica, while other breeding groups live in Japan, the Galapagos, Hawaii and Atlantic islands. That is a general range statement, not a breeding record from Costa Rica.

When to see it

One was photographed in the morning of 27 March 2022 on the ocean route to Isla del Coco. Another was seen on the afternoon of 31 August 2020, flying low around the boat near the island.

Similar birds

Leach's Storm-Petrel is the bird to rule out. It has a more angular wing with a clear bend at the wrist, a longer and more clearly notched tail, and a broader, duller rump patch, often with a dark centre line. Its broad pale wing-bar reaches the front edge of the wing, whereas on Band-rumped the paler bar usually stops short, though worn birds show more contrast.

Names and lore in Costa Rica

The official Spanish name on the Costa Rican bird list is Paiño Rabifajeado. The list also gives Spanish names for the other storm-petrels, such as Paiño de Leach.

Status and conservation

The online official list shows it as M (migratory), but a Costa Rican oceanic birds article lists it as accidental, and a 2023 paper proposes changing its status to Accidental.

Photography tips

Watch the water around the boat. The 2020 bird flew very low over the sea around the vessel, and the 2022 bird was photographed on the ocean route at 9:30 in the morning.