The ashy storm petrel (Hydrobates homochroa) is a small, scarce seabird of the storm petrel family Hydrobatidae. It breeds colonially on islands off the coasts of California and Mexico, and is one of six species of storm petrel that live and feed in the rich California Current system.

Taxonomy

The ashy storm petrel was first described by American ornithologist Elliott Coues in 1864. Both its common and scientific name, homochroa, "uniformly colored", from Ancient Greek (h)omoia (όμοια), "alike" + "chroma" (χρώμα) "color", come from its coloration.

It was formerly defined in the genus Oceanodroma before that genus was synonymized with Hydrobates.

Description and ecology

This is a small, uniformly sooty-brown storm petrel with a forked tail, closely resembling the black storm petrel, but it is smaller and has a more fluttering style of flight, with the upstroke only becoming horizontal to the body before beginning the downstroke (other storm petrels in its range have a higher upstroke).

It is a gregarious bird at sea, feeding nocturnally on cephalopods, fish (particularly the deep-sea myctophids, which rise to the sea's surface at night) and euphausiid krill such as Thysanoessa spinifera, which also swarm at the surface. They also attend fishing vessels for the fish oils released when the nets are pulled.

thumb|Egg (coll.[[MHNT) ]]

Ashy storm petrels nest in rock burrows on offshore islands, returning to the nests at night. The species has a long breeding cycle, laying eggs in May and fledging in October, although timing varies greatly, more so than in most other storm petrels; some pairs may have a chick that is half grown when other pairs are still laying. Like in many other seabirds, pairs show both mate and site fidelity, mating in the same pair with the same mate for many years and nesting at the same burrow, despite the pairs spending their lives out of the breeding season separate from each other, and despite the fact that many individuals might seem to compete for burrows at the nesting colonies. A change in mate is usually associated with a change in nesting site.

The ashy storm petrel is a long-lived bird; a banded individual has lived at least 31 years. Outside of the breeding season, it is believed to be more widely distributed, foraging on the California Current, but it undertakes no large migration and does not range as far as other species of storm petrels. In the early fall, large flocks can be seen in Monterey Bay. The birds do not range inland any significant distance except when storm-blown; for example, a sighting in San Mateo County, California was considered "unusual" by an experienced naturalist.

Further reading

  • Ainley, D. (1995): Ashy Storm Petrel (Oceanodroma homochroa). In: Poole, A. & Gill, F. (eds.): The Birds of North America: 185. Academy of Natural Sciences, Philadelphia, PA & American Ornithologists' Union, Washington, D.C. Online version.
  • Brooke, Michael (2004): Albatrosses and Petrels across the World. Oxford University Press, Oxford, New York.
  • Ashy storm petrel Species Account – Cornell Lab of Ornithology
  • Species factsheet - BirdLife International