The Ashy Storm-petrel (Oceanodroma homochroa) is a small, scarce seabird of the storm-petrel family Hydrobatidae. Breeding colonies can be found on islands off the coasts of California and Mexico, and it is one of 6 species of storm petrel that live and feed in the rich California Current system. Both its common and scientific names come from its coloration; one authority has suggested naming it Coues’s Storm Petrel after the man that described the species, Elliott Coues.
This is a small, uniformly sooty-brown storm petrel with a forked tail. It closely resembles 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). It is a gregarious bird at sea, and prefers to feed 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 will also follow fishing vessels for the fish oils released when the nets are pulled. It nests in rock burrows on offshore islands, returning to the nests at night. The breeding cycle is rather long; females lay eggs in May and fledging occurs in October, although timing varies greatly, more so than most other storm-petrels. Some pairs may have a chick that is half grown when other pairs are still laying. Like many other seabirds, pairs show both mate and site fidelity, mating in the same pair with the same mate for many years. A change in mate is usually associated with a change in nesting site.
Distribution and Status
The Ashy Storm-petrel breeds on 17 islands in the northeast Pacific, principally off California, but also northwestern Mexico. Half of the world’s population of this bird nests on the Farallon Islands, off San Francisco. Other breeding islands include the 8 Channel Islands of California (San Miguel Island, Santa Cruz Island, Anacapa Island, Santa Barbara Island, Santa Catalina Island and San Clemente Island), and a small population can be found on Mexico’s Coronados. Most of the islands that it breeds on are covered by some degree of protection. Outside of the breeding season it is believed to be more widely distributed, foraging on the California Current, but undertakes no large migration and doesn’t range as far as other species of storm-petrel. In the early fall large flocks can be seen in Monterey Bay. The world population is estimated to be around 10,000 birds, 8,000 of them breeders, the Farallon population having declined by one third between 1972 and 1992. The species is considered has recently been listed as endangered and is 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.