Hydrobates homochroa

Ashy Storm-petrel

Family: Hydrobatidae · Class: Aves · Order: Procellariiformes

Conservation status: G2 S2

The Ashy Storm-petrel is a small seabird measuring approximately 19-22 cm (7.5-8.7 inches) in length with a wingspan of 43-46 cm (17-18 inches). This species displays uniformly dark smoke-gray plumage that distinguishes it from other Pacific storm-petrels. The wings appear slightly brownish, and the tail is moderately forked. Like other storm-petrels, it has tube-shaped nostrils on top of its bill and webbed feet adapted for surface feeding. The Ashy Storm-petrel has the most northerly distribution among dark storm-petrel species nesting along the Pacific coast. Its range extends from northern Baja California, Mexico, to northern California, with breeding sites located at 33 confirmed locations along the California coast (USFWS 2023). The largest breeding concentration occurs on the South Farallon Islands in central California, while four other major concentrations exist in southern California on the Channel Islands, particularly on or adjacent to San Miguel and Santa Barbara islands, and on northwest and northeast Santa Cruz Island. This species inhabits xeric islands for nesting and forages in near-coast waters of the California Current System. Ashy Storm-petrels nest in rocky crevices, caves, and under vegetation on offshore islands. Unlike most storm-petrels, this species is nonmigratory and remains near its breeding areas year-round, except during autumn molt periods. The species frequents offshore waters within the highly productive California Current ecosystem for foraging. Ashy Storm-petrels are nocturnal at breeding sites, arriving and departing only under cover of darkness. They feed by surface-picking and pattering across the water to capture small fish, squid, and crustaceans from the ocean surface. The species exhibits strong site fidelity, returning to the same nesting areas annually. Breeding occurs during spring and summer months, with birds nesting in colonies on rocky islands. The global breeding population is estimated at approximately 8,200 individuals, with a range of 3,000-13,250 birds (Birds of the World 2023). The U.S. Fish and Wildlife Service designated the Ashy Storm-petrel as a Bird of Conservation Concern in 2002, and it maintains this status in Marine Bird Conservation Regions 17 and 32 as of December 2025. The species holds a global rank of G2 (imperiled) and a California state rank of S2 (imperiled). A petition to list the species as threatened or endangered under the Endangered Species Act was submitted in 2007. California Department of Fish and Wildlife has listed the Ashy Storm-petrel as a Species of Special Concern. Primary threats include predation by Western Gulls, whose populations have increased substantially in recent decades, and impacts from introduced rodents on larger nesting islands. Oil spills and marine pollution pose additional risks to this species that depends entirely on marine environments. Climate change may affect prey availability within the California Current System, potentially impacting foraging success.

Data from The California Species Project — 14,000+ California species with verified data from CNPS, CDFW, USFWS, and more.