Ashy Storm-Petrel

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Common Name: Ashy Storm-petrel
Scientific Name: Oceanodroma homochroa

Size: 7.8 inches (20 cm)

Habitat: North America; breeds on a small number of island groups and offshore rocks within the California Current System. Breeding has been confirmed at only six major island groups (South Farallon, San Miguel, Santa Cruz, Santa Barbara, San Clemente, and Los Coronado Islands) and three groups of offshore rocks (Castle Rock/Hurricane Point, Double Point, and Bird Rocks). Major colonies, containing the vast majority of the world population, occur on the South Farallon Islands in central California and the Channel Islands in southern California, primarily at Prince Island off San Miguel Island, Santa Barbara Island, and Santa Cruz Island. At sea, Ashy Storm-petrels remain within the central and southern California Current System year-round, preferring continental slope waters (200-2000 m deep) that are within a few kilometers of the coast in some areas (e.g. Monterey Bay) and more than 50 km offshore in other areas (e.g. Gulf of the Farallones). High densities are known to congregate in some areas, e.g. the continental shelf-break in the western Santa Barbara Channel, and in the Santa Cruz Basin that separates Santa Cruz, San Nicolas, and Santa Barbara Islands. Autumn congregations of 4000-6000 birds have been recorded in Monterey Bay. The breeding population has been estimated at 5,200-10,000 individuals, with about half breeding on the South Farallon Islands and half in the Channel Islands.

Status: Endangered. Global Population: 5,200 - 10,000 Mature individuals and decreasing. Foraging areas are threatened by organochlorine and oil pollution. At Anacapa Islands, introduced rats have probably reduced colony size, though these rats have now been eradicated. Predation by expanding Western Gull (Larus occidentalis) populations, as well as Burrowing Owls (Speotyto cunicularia) and Barn Owls (Tyto alba), may be partly responsible for keeping numbers low at South Farallon, Santa Barbara and Anacapa islands. Bright lights used by near-shore squid fishing and other commercial and recreational vessels during the breeding season could increase predation levels, as well as cause mortality by attraction to lighted structures. Ashy Storm-petrels are sensitive to human disturbance at their nest sites and may abandon their nests with frequent disturbance. Consequently, disturbance from sea kayaker visits is a potential threat to nesting birds. Future changes in climate could also affect this species, for example through declines in primary productivity associated with warming and reduced upwelling, sea level rises affecting nest site availability, or the effects of ocean acidification (caused by increasing carbon dioxide absorption) on crustacean prey species.

Most of the Californian population nest on protected and specially managed islands.

Diet: Planktonic crustaceans and small fish (sardines and anchovies). Birds feed at sea and visit the colony at night. Foraging during the breeding season occurs mainly over continental shelves.

Breeding: Breeds in rock crevices and burrows in colonies on offshore islands. The breeding season is protracted, and eggs are laid asynchronously, with some pairs laying eggs while other pairs are in the midst of chick-rearing. At Southeast Farallon Island, Ashy Storm-petrels visit the colony year-round, and most breeding activity is concentrated in February through October. At Santa Cruz Island, Ashy Storm-petrel nesting activity spans March through December. Like in many other seabirds, pairs show both mate and site fidelity, the same pair mating 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.

Cool Facts: The Ashy Storm-petrel is difficult to identify. It is an all dark Storm-petrel with a pale wash on the underwing that forms a distinct bar. That is an important feature, as are the pale grey edges of the uppertail coverts. This is a small, uniformly sooty-brown storm petrel with a forked tail, closely resembling the Black Storm-petrel, however 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).

The Ashy Storm-petrel is a long-lived bird; a banded individual has been recorded living at least 31 years.

Found in Songbird ReMix Threatened, Endangered, Extinct 3

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