Ashy Storm-Petrel

Oceanodroma homochroa

(c) Glen Tepke
  • HYDROBATIDAE
  • Storm-petrels
  • Procellariiformes
  • Paiño Ceniciento
  • Océanite cendré
Introduction

Among the four dark storm-petrels nesting on North America's west coast islands, the Ashy Storm-Petrel is the most northern. Confined to California islands and nearby waters, this smoke-gray seabird blends in well with its foggy environment. Like other storm-petrels, Ashy Storm-Petrels arrive and depart their breeding colonies only at night; unlike most others, they do not travel far from their colonies after breeding, and the breeding season is spread out over many months.

Appearance Description

This small seabird weighs 1.3 ounces, and is eight inches in length, with a wingspan of 18 inches. The Ashy Storm-Petrel, as the name implies, is an entirely gray seabird roughly the size of a Purple Martin, with a forked tail. It is smaller and grayer than the similar Black and Leach's Storm-Petrels, but larger than the Least Storm-Petrel—the other dark species found in the area.

Range Distribution

The Ashy Storm-Petrel can only be found on the islands off California and in the adjacent waters. This species' limited year-round range extends from Cape Mendecino, California to northern Baja, just south of the U.S. - Mexico border. Breeding colonies occur on offshore islands in the area, including the Southeast Farallons, San Miguel, Santa Barbara, Santa Cruz, Anacapa, San Clemente and Los Coronados (in Mexico). On most of the larger islands listed above, breeding occurs on outlying rock formations, free of mammalian predators.

Habitat

Ashy Storm-Petrels feed near their nesting islands in the offshore waters of the California current, one of the richest regions of the world ocean. The birds breed on rocky islands among talus slopes, from just above sea level to the highest, interior portions of nesting islands. Smaller islands and offshore rocks where resources are not sufficient normally to sustain predatory mammals such as rats and foxes are preferred for nesting.

Feeding

The diet of Ashy Storm-Petrels includes small fish, young squid, and crustaceans, which it finds on the ocean surface at night. Spiny lobster young have been found in the stomachs of Ashy Storm-Petrels in their southern range. These petrels feed mostly at night; sightings of feedings during the day are rare. Known to scavenge, they are attracted to fishing vessels hauling their nets and to fish-oil slicks. Food is obtained by sitting on the water and, if the prey item is large, by tearing pieces off with the bill. Birds also pick small prey items, such as crustaceans, from the sea surface using the beak as they hover into the wind, especially when preying on one euphausiid (Thysanoessa spinifera) that swarms at the sea surface. Unfortunately, items ingested also include plastic particles that are now common on the sea surface.

Reproduction

Ashy Storm-Petrels nest in cavities on offshore islands and move to and from their colonies at night, which may help them avoid predation by gulls, falcons, owls and other enemies. Nest cavities are hidden among the rock crevices, generally on the driest portion of islands, where vegetation is not so dense. Little if any nest material is used inside the cavity. Like other storm petrels, female Ashy Storm-Petrels lay only one white egg, sometimes marked with faint red-brown dots. Both sexes incubate the egg for about 45 days. Chicks are fed via regurgitation by both parents and head off to sea about 84 days after hatching. Periods of incubation and chick growth are very long by avian standards. The chicks of some pairs can be half grown at the time when other pairs lay their egg.

Migration

Ashy Storm-Petrels do not perform long-distance migration. Individuals may disperse, but not to great distances and only during the molting period in the autumn.

  • 5,000-15,000
  • 5,000-15,000
Population Status Trends

The nocturnal nature of this species and its hidden nests make it difficult to assess population trends. Long-term records for the Farallon Islands show no significant changes from the 1880s to 1970; neither do counts of birds at sea off Monterey Bay from the mid-1970s to the mid 1990s. However, severe population declines have been found over a 20-year period at the main nesting colonies in the Farallon Islands. Due to its restricted range, very small population size, and indications of strong population decline, this species warrants an immediate increase in focused monitoring.

Conservation Issues

Because of the small range and population size of the species and the evidence of a severe population decline, BirdLife International (on the behalf of the World Conservation Union [IUCN]), now lists this species as Endangered.

The limited range of this species makes it susceptible to local disasters such as an oil spill, particularly on Monterey Bay in the fall, when most of the world's population is present there. The ingestion of plastic also harms Ashy Storm-Petrels by reducing the amount of food they ingest; birds that have ingested large loads of plastic weigh significantly less than those that have not.

The species is particularly susceptible to loss of coastal upwellings. Coastal upwellings have been particularly unpredictable along the California coast in recent years and are predicted to decline further in the face of global warming and its effects on ocean currents and upwellings.

Increased populations of Western Gulls—predators of Ashy Storm-Petrels—at a number of breeding sites, are cause for concern. Ashy Storm-Petrel breeding colonies are also susceptible to introduced mammalian predators including mice, rats, and cats. Ashy Storm-Petrels are sensitive to disturbance, including that generated by researchers, especially during the incubation period. Daily nest-checking has led to reductions in reproductive success.

Although these factors do not bode well for positive growth in Ashy Storm-Petrel populations, nesting colonies are distributed among at least 17 localities, almost all of which are protected from development and human encroachment. Most Ashy Storm-Petrel breeding colonies fall within protected areas in California, including the Channel Islands N. P., and the Farallon National Wildlife Refuge and Wilderness Area. The legislative protection conferred upon these islands is important in assuring the health of Ashy Storm-Petrels and other species found there.

What You Can Do

U.S. National Parks and Wildlife Sanctuaries provide refuge for Ashy Storm-Petrels in California, and other species throughout the U.S. Unfortunately, the park service is often overlooked during the U.S. government's budgeting process. Read how you can help gain much needed funding for U.S. National Wildlife Refuges.

The non-profit group Island Conservation is working to preserve seabird habitats, including Ashy Storm-Petrels, on islands in Baja California, Mexico, and off the California coast.  Learn more about their mission, and how you can help. 

Find out what you can do including Audubon programs and activities.

More Information

Audubon's Important Bird Area program is an important tool for the conservation of Ashy Storm-Petrels as well as other species. Learn more about the Important Bird Areas where Ashy Storm-Petrels nest.

Learn more about this species and other birds through these resources

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Natural History References

Ainley, D. 1995. Ashy Storm-Petrel (Oceanodroma homochroa). In The Birds of North America, No. 185 (A. Poole and F. Gill, Eds.). The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists' Union, Washington, D. C.

BirdLife International (2006) Species Factsheet: Oceanodroma homochroa, Ashy Storm-petrel

Cooper, D. S. California Important Bird Areas. Audubon California, Sacramento, CA. 2002.

Conservation Status References

Ainley, D. 1995. Ashy Storm-Petrel (Oceanodroma homochroa). In The Birds of North America, No. 185 (A. Poole and F. Gill, Eds.). The Academy of Natural Sciences, Philadelphia, PA, and The American Ornithologists' Union, Washington, D. C.

BirdLife International (2006) Species Factsheet: Oceanodroma homochroa, Ashy Storm-petrel

Cooper, D. S. California Important Bird Areas. Audubon California, Sacramento, CA. 2002.