Islands near San Francisco. Other breeding islands include the eight Channel Islands of California and a small population on Mexico's Coronados. Bat Cave, on the north side of Santa Cruz Island in Southern California, has the largest nesting colony for the ashy storm petrel in the world, with over 100 nests. 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. The world population is estimated to be around 10,000 birds, 8,000 of them breeders, with the Farallon population having declined by one-third between 1972 and 1992. The ashy storm petrel is designated as a species of conservation concern in California. It is threatened by western gull and burrowing owl predation, illumination from fishing boats, introduced predators such as rats and feral cats, and pollution. Most of the islands were it breeds are covered by some degree of protection. Global warming could have a profound impact on ashy storm petrels. Future changes to coastal California waters due to global warming could result in warmer, less productive waters, which would mean less food would be available for the petrels. In addition, ocean acidification may result in a decline of crustacean prey species due to the effects that excess CO2 will have on the animals' shells. Sea-level rise will also threaten certain nesting sites that would be located too close to water. References 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. External links Species factsheet - BirdLife International ashy storm petrel Birds of Mexico Native birds of the West Coast of the United States Ashy storm petrel Ashy storm petrel Ashy storm petrel Ashy storm petrel Ashy storm petrel ashy storm petrel ashy storm petrel