Last updated: May 21, 2021
Place
Ashy Storm-Petrel
Ilana Nimz/ PRBO Conservation Science
Scientific Name
Oceanodroma homochroa
Introduction
The ashy storm-petrel relies upon the isolated breeding grounds of the Channel Islands National Park to ensure its successful reproduction. Due to its sensitivity to outside influences that impact its numbers, the park has proved to be a major component in its vitality. The park's success in removing non-native species such as the black rat that have preyed upon nesting birds has been a factor in the increase in many of the susceptible seabird populations.
Quick and Cool Facts
- Ashy storm-petrel breeds on 17 islands in the northeast Pacific, principally off California, but also northwestern Baja California, Mexico.
- They have a restricted range and a small global population of approximately 10,000 birds.
- Fifty percent of the world's population of ashy storm-petrels breed on San Miguel, Santa Barbara, Santa Cruz and Anacapa islands.
- They mate in the same pair with the same mate for many years and nest at the same burrow.
- Ashy Storm-Petrels nest in rock crevices along cliffs, offshore rocks, and under driftwood in sea caves.
- Ashy storm-petrels have a long breeding cycle, laying just one egg in May and fledging in October.
- Ashy storm-petrels depart from and return to the nest at night to avoid predators.
- Petrels "patter" on the ocean's surface to gather prey items including squid, fish and krill.
- Ashy storm-petrels can live to 34 years old.
- The ashy storm-petrel is listed as species of special concern by the California Department of Fish and Game.
Appearance
The ashy storm-petrel, as the name implies, is an entirely gray seabird with a forked tail, roughly the size of a purple martin. This small seabird weighs 1.3 ounces and is eight inches in length, with a wingspan of 18 inches. 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
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 Mendocino, California, to northern Baja, just south of the US- Mexico border. Breeding colonies occur on offshore islands in the area, including the Southeast Farallon islands, San Miguel, Santa Barbara, Santa Cruz, Anacapa, San Clemente and Mexico's Coronados islands. 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
It is a gregarious bird at sea, feeding nocturnally on squid, loligo opalescens, fish (particularly lanternfishes myctophids, which rise to the sea's surface at night) and krill, which also swarm at the surface. They are also attracted to fishing vessels for the fish oils released when the nets are pulled. During the breeding season, foraging coincides spatially and seasonally with the spawning aggregations of sardines and anchovies.
Reproduction
Ashy storm-petrels nest in rock burrows on offshore islands, returning to the nests at night. The species has a long breeding cycle, laying eggs in May and fledging in October, although timing varies greatly, more so than in most other storm-petrels: some pairs may have a chick that is half grown when other pairs are still laying. Like in many other seabirds, pairs show both mate and site fidelity. They mate in the same pair with the same mate for many years and nest at the same burrow. This is intriguing since the pairs spend their lives out of the breeding season separate from each other, and despite the fact that many individuals might seem to compete for burrows at the nesting colonies. A change in mate is usually associated with a change in nesting site.
Migration
Like other storm-petrels, ashy storm-petrels arrive and depart their breeding colonies only at night. 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.
Conservation Status
The ashy storm-petrel is listed as species of special concern by the California Department of Fish and Game. The limited range of this species makes it susceptible to local disasters such as an oil spill. The species is particularly susceptible to loss of coastal upwellings that have been unpredictable along the California coast in recent years and are anticipated to decline further in the face of global warming. 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, especially during the incubation period. Most ashy storm-petrel breeding colonies fall within protected areas in California, which includes Channel Islands National Park. The park's success in removing non-native species such as the black rat that have preyed upon nesting birds has been a factor in the increase in many of the susceptible seabird populations such as the ashy storm-petrel. Visit Seabirds for more information about restoration activities in the park.
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