Least Storm-Petrel

How to find it

Going out on a boat is the way to see storm-petrels. On a pelagic day trip off the Pacific coast, the specialty birds showed up about one or two hours after leaving port. Local guides run pelagic trips from Cabuya, on the Nicoya Peninsula, though species vary by season and other factors, so no two trips show the same birds. The Puntarenas to Paquera ferry ride lasts about an hour, and the deepest water is about half an hour out of Puntarenas. One or two Least Storm-Petrels have been reported from it, though none came very close to the boat. A day pelagic trip on a sailboat from the Los Sueños marina found them, though surprisingly few that day.

How to recognise it

This is a tiny bird, about 15 cm long and about 19 g, and the smallest storm-petrel in the Pacific.

Look for these marks:

- Blackish brown plumage all over.

- A paler bar across the upper wing.

- A short, wedge-shaped tail.

- A bat-like look in flight.

Size is the best clue. It is clearly smaller than the other all-dark storm-petrels, such as Black and Leach's, and it is about the size of a sparrow.

Behaviour and diet

It flies low over the water, often in the troughs between waves, with fast, deep wingbeats. That gives it the batlike look. Its flight is weaker and more undulating than that of the larger dark storm-petrels, and is often fluttering.

It travels in loose groups, usually with Black Storm-Petrels. Its diet is mostly small plankton.

One birder spotted a Least Storm-Petrel working a drift line in the Gulf of Nicoya. Another saw one flying low among flocks of Black Terns, with quick, snappy wingbeats.

Where it lives

This is a pelagic species, so its home is open sea. In Costa Rica it occurs in Pacific waters, including the Gulf of Nicoya and offshore along the Pacific coast.

Away from here it breeds almost only in the Gulf of California, plus three islands off western Baja California. From September to June it wanders at sea, as far south as the equator, and it winters south to Ecuador.

When to see it

In the Gulf of Nicoya it is uncommon from July to November and common from December to June. Offshore along the Pacific coast it is an uncommon migrant in autumn and a common migrant in spring, from April to June.

Similar birds

In the Gulf of Nicoya the two likeliest storm-petrels are Black and Least. Birders found Least easy to tell from larger storm-petrels by its bat-like flight, while Black Storm-Petrels look like shadowy nighthawks zipping low over the waves. Black Storm-Petrel is about tern-sized, so a small all-dark bird that is smaller than nearby terns, with quick wingbeats, points to Least.

Names and lore in Costa Rica

The Costa Rican Spanish name on the official list is Paiño Menudo.

Status and conservation

The Least Storm-Petrel is a non-breeding visitor and winter resident in Costa Rica (M on the AOCR list), and the IUCN lists it as Least Concern.

Photography tips

At the Puntarenas lighthouse, morning and late afternoon are best for storm-petrels, though one birder has seen them at midday. Birds tend to come closer to shore at this bottleneck between the outer and inner gulf.