Oceanodroma microsoma

Least Storm-Petrel

Family: Hydrobatidae · Class: Aves · Order: Procellariiformes

The Least Storm-Petrel (Oceanodroma microsoma) is the smallest member of the storm-petrel family, measuring 13-15 cm (5.1-5.9 inches) in length with a wingspan of 32 cm (12.6 inches). Adults weigh 18-20 grams (0.6-0.7 ounces), making this species one of the smallest seabirds in North America. The plumage is predominantly dark sooty brown to blackish-brown, with a slightly paler rump patch. The wings are relatively broad for the bird's small size, and the tail is square to slightly forked. The bill is small and black with hooked tip typical of petrels, and the legs are black with webbed feet. The Least Storm-Petrel has a limited breeding range, nesting primarily on islands off the Pacific coast of Baja California, Mexico, including the San Benito Islands, Guadalupe Island, and several smaller islets. In California waters, the species occurs as a regular visitor during post-breeding dispersal from August through October, when individuals move northward along the coast. They are most commonly observed in offshore waters from San Diego County north to Monterey County, typically remaining beyond the continental shelf in deep oceanic waters. This pelagic species inhabits open ocean environments, preferring warm temperate to subtropical waters. During the breeding season, they nest on rocky islands with suitable crevices and caves. The species shows preference for areas where upwelling creates productive feeding conditions, typically found in waters deeper than 200 meters where surface temperatures range from 15-22°C (59-72°F). They rarely approach shore except during severe weather events. Least Storm-Petrels are nocturnal at breeding colonies and feed primarily by surface-seizing and shallow plunging, capturing small fish, squid, and zooplankton. Their diet consists largely of larval fish, copepods, and small cephalopods. The species breeds colonially in rock crevices and burrows, with the breeding season extending from May through September. Females lay a single white egg, and both parents share incubation duties for approximately 40 days. Chicks fledge after 60-70 days. Adults are highly pelagic outside the breeding season, spending months at sea without returning to land. The species is not federally or state listed in the United States, but populations face threats from introduced predators at breeding colonies, including cats and rats on Mexican islands. Climate change poses additional concerns through potential shifts in ocean productivity and prey availability. Oil spills and plastic pollution in marine environments represent ongoing threats to this small seabird. The total population is estimated at fewer than 10,000 individuals, with the majority breeding on Mexican islands. Conservation efforts focus on predator control at breeding sites and marine protected areas within foraging ranges.

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