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Ashy Storm Petrel | Hydrobates homochroa
Californisch stormvogeltje | Paíño ceniciento
The Ashy Storm Petrel is a medium-sized, uniformly grey-brown storm petrel without a white rump that occurs almost only in the cool California Current. Most of the small world population breeds on islands off California. In the guide area it is restricted to the far north-west, where a few small colonies lie on islets off northern Baja California.
Voice
Silent at sea. At the colony, which is visited only at night, a soft, husky purring and twittering comes from the rock crevices.
Recording: Matthew L. Brady — CC BY-NC-SA 4.0 · shortened to the first 60 s, mono · xeno-canto
Identification
18–20 cm. A medium-sized storm petrel with fairly short, rounded wings and a long, moderately forked tail. The plumage is uniformly dark grey-brown, slightly greyer and less black than in the other dark species, without a pale rump. The pale band across the upperwing is faint; on the underside of the wing a pale stripe across the coverts can be seen. Male, female and young birds are alike. The flight is fluttering and fairly direct, with shallow beats in which the wings barely rise above the body.
Confusion species
The Black Storm Petrel Hydrobates melania is larger and blacker, with longer wings, a more deeply forked tail and slow, deep beats; it lacks the pale underwing stripe. The Least Storm Petrel Hydrobates microsoma is much smaller, with a short, wedge-shaped tail. Dark-rumped Leach's Storm-Petrels Hydrobates leucorhous and Townsend's Storm Petrels Hydrobates socorroensis have a more distinct pale upperwing band and longer, angled wings, and fly in a more bounding way.
Habitat
Cool water over the continental shelf and its edge, especially in upwelling areas. Takes small crustaceans, fish larvae and small squid from the surface in flight. Breeds in rock crevices, sea caves and among boulders on small islands.
Where the bird is most at home, classified by the vegetation units of Mexico and Central America.
Range and movements
Breeds mainly on islands off California, from the north of the state to the Channel Islands. In the guide area only in small numbers on islets off northern Baja California, south to Isla Todos Santos. Hardly migrates and stays in the California Current year-round; in the guide area it is only to be expected in the cool waters off north-western Baja California. Records in the guide area are scarce, and the present size of the Mexican colonies is poorly known.
- Summer visitor (c. Apr–Sep)
- Passage (Mar–Apr, Oct–Nov)
- dark = core range, pale = thinly spread
How and when to look
Only on boat trips in the cool waters off north-western Baja California, for example around the islets off Ensenada, and rare even there. Look for the grey-brown colour, the pale underwing stripe and the shallow, fluttering flight.
Conservation status
Endangered. The world population is small and concentrated on a few islands, where numbers have declined. Threats are predation by gulls, owls and introduced mice and cats, artificial light, oil pollution and disturbance of the breeding sites.
Scientific name
Hydrobates homochroa | (Coues, 1864)
Coues described the species in 1864 as Cymochorea homochroa; because it was later moved to another genus, the author and year stand in brackets. The genus Hydrobates was introduced in 1822 by Boie. Hydrobates is Greek, from hudro- 'water' and batēs 'walker': 'water walker'. homochroa is Greek homokhroos 'uniformly coloured', from homos 'same' and khroa 'colour', after the plain grey-brown plumage. The specimen the first description was based on came from Farallon Islands, California.