Least Storm Petrel (Hydrobates microsoma) — Vorstman's Guide to the Birds of the Andes and West Coast

Voice

Silent at sea. At the breeding colonies a fast, rattling and purring sound comes from the nest cavities at night.

No recording with a suitable Creative Commons licence is available for this species yet.

Identification

13–15 cm, a very small, all blackish-brown storm petrel with relatively short, broad wings and a short, wedge-shaped to rounded tail without a fork. A faint pale bar crosses the upperwing. Flight is fast and low over the water, with deep wingbeats, recalling a bat. The sexes are alike.

Confusion species

Black Storm Petrel Hydrobates melania and Markham's Storm Petrel Hydrobates markhami are much larger, with long, deeply forked tails and a calmer flight. Wedge-rumped Storm Petrel Hydrobates tethys is slightly larger and has a large white rump. Wilson's Storm Petrel Oceanites oceanicus also has a white rump and feet that project beyond the tail.

Habitat

At sea, especially warm water over the continental shelf and its edge, often in flocks with other storm petrels. It picks small crustaceans and fish larvae from the surface in flight. It breeds in crevices and among boulders on bare islands outside the guide area.

Where the bird is most at home, classified by the vegetation units of the Andes and the west coast.

Range and movements

At sea along the Pacific coast of Colombia and Ecuador, mainly in the northern winter; scarce off northern Peru and rare farther south. Does not breed in the guide area and is absent from Bolivia. Outside the guide area it breeds on islands in the Gulf of California and off the west coast of Baja California in Mexico.

Resident
Winter visitor (c. Oct–Mar)
dark = core range, pale = thinly spread

Density map from the occurrence records of GBIF (2006-10-01 – 2026-09-30), counted per 1.41° grid cell and per month and divided by all bird records in that same cell — so the number of birdwatchers does not shape the picture. Colour depth follows that share and fades out gradually, so the map does not follow national borders. Country outlines: Natural Earth (public domain).

How and when to look

Look for it on pelagic trips off the coast of Ecuador among flocks of Black Storm Petrels; in mixed flocks the small size, short tail and fast wingbeat stand out first.

Conservation status

Least Concern. Introduced rats and cats and disturbance of the breeding islands are the main threats.

Scientific name

Hydrobates microsoma | (Coues, 1864) (GBIF: Oceanodroma microsoma)

Coues described the species in 1864 as Halocyptena microsoma; because it was later moved to another genus, the author and year stand in brackets. The genus Hydrobates was introduced in 1822 by Boie. The genus name comes from Greek hudro-, 'water-', and batēs, 'walker', for the pattering over the water surface while feeding. The species name comes from Greek mikros, 'small', and sōma, 'body': it is the smallest storm petrel in the Americas. The specimen the first description was based on came from San José del Cabo, Baja California Sur, Mexico.