The ashy storm petrel (''Hydrobates homochroa'') is a small, scarce

seabird Seabirds (also known as marine birds) are birds that are adapted to life within the marine environment. While seabirds vary greatly in lifestyle, behaviour and physiology, they often exhibit striking convergent evolution, as the same envir ...

of the storm petrel family Hydrobatidae. It breeds colonially on islands off the coasts of

California California is a state in the Western United States, located along the Pacific Coast. With nearly 39.2million residents across a total area of approximately , it is the most populous U.S. state and the 3rd largest by area. It is also the m ...

and

Mexico Mexico (Spanish language, Spanish: México), officially the United Mexican States, is a List of sovereign states, country in the southern portion of North America. It is borders of Mexico, bordered to the north by the United States; to the so ...

, and is one of six species of storm petrel that live and feed in the rich California Current system.

Taxonomy

The ashy storm petrel was first described by American ornithologist Elliott Coues in 1864. Both its common and scientific name, ''homochroa'', "uniformly colored", from

Ancient Greek Ancient Greek includes the forms of the Greek language used in ancient Greece and the ancient world from around 1500 BC to 300 BC. It is often roughly divided into the following periods: Mycenaean Greek (), Dark Ages (), the Archaic pe ...

(h)omoia (''όμοια''), "alike" + "chroma" (''χρώμα'') "color", come from its coloration. It was formerly defined in the genus '' Oceanodroma'' before that genus was synonymized with '' Hydrobates''.

Description and ecology

This is a small, uniformly sooty-brown storm petrel with a forked tail, closely resembling the

black storm petrel The black storm petrel (''Hydrobates melania'') is a small seabird of the storm petrel family Hydrobatidae. It is 23 cm in length, with a wingspan of 46–51 cm. The species breeds colonially on islands off the southern California c ...

, but 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, feeding nocturnally on

cephalopod A cephalopod is any member of the molluscan class Cephalopoda ( Greek plural , ; "head-feet") such as a squid, octopus, cuttlefish, or nautilus. These exclusively marine animals are characterized by bilateral body symmetry, a prominent head ...

fish Fish are Aquatic animal, aquatic, craniate, gill-bearing animals that lack Limb (anatomy), limbs with Digit (anatomy), digits. Included in this definition are the living hagfish, lampreys, and Chondrichthyes, cartilaginous and bony fish as we ...

(particularly the deep-sea

myctophid Lanternfishes (or myctophids, from the Greek μυκτήρ ''myktḗr'', "nose" and ''ophis'', "serpent") are small mesopelagic fish of the large family Myctophidae. One of two families in the order Myctophiformes, the Myctophidae are represent ...

s, which rise to the sea's surface at night) and euphausiid krill such as ''

Thysanoessa spinifera Thysanoessa Abstract ''Thysanoessa'' is a genus of the krill that play critical roles in the marine food web. They're abundant in Arctic and Antarctic areas, feeding on zooplankton and detritus to obtain energy. Thysanoessa are responsible for ...

'', which also swarm at the surface. They also attend fishing vessels for the fish oils released when the nets are pulled. Oceanodroma homochroa MHNT ZOO 2010 11 42 California Naurois

Oceanodroma homochroa MHNT ZOO 2010 11 42 California Naurois

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 Fledging is the stage in a flying animal's life between hatching or birth and becoming capable of flight. This term is most frequently applied to birds, but is also used for bats. For altricial birds, those that spend more time in vulnerable ...

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, mating in the same pair with the same mate for many years and nesting at the same burrow, despite the pairs spending 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. The ashy storm petrel is a long-lived bird; a banded individual has lived at least 31 years.

Distribution, status, and threats

Ashy storm petrels breed on 17 islands in the northeast Pacific, principally off the coast of

, but including a few sites off the coast of northwestern

. Half the world's population nests on the

Farallon Islands The Farallon Islands, or Farallones (from the Spanish ''farallón'' meaning "pillar" or "sea cliff"), are a group of islands and sea stacks in the Gulf of the Farallones, off the coast of San Francisco, California, United States. The isl ...

near

San Francisco San Francisco (; Spanish for " Saint Francis"), officially the City and County of San Francisco, is the commercial, financial, and cultural center of Northern California. The city proper is the fourth most populous in California and 17t ...

. 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 San Mateo County ( ), officially the County of San Mateo, is a county located in the U.S. state of California. As of the 2020 census, the population was 764,442. Redwood City is the county seat, and the third most populated city following Dal ...

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 The western gull (''Larus occidentalis'') is a large white-headed gull that lives on the west coast of North America. It was previously considered conspecific with the yellow-footed gull (''Larus livens'') of the Gulf of California. The western ...

and burrowing owl predation, illumination from fishing boats,

introduced predators An introduced species, alien species, exotic species, adventive species, immigrant species, foreign species, non-indigenous species, or non-native species is a species living outside its native distributional range, but which has arrived there ...

such as rats and

feral cat A feral cat or a stray cat is an unowned domestic cat (''Felis catus'') that lives outdoors and avoids human contact: it does not allow itself to be handled or touched, and usually remains hidden from humans. Feral cats may breed over dozens ...

s, and

pollution Pollution is the introduction of contaminants into the natural environment that cause adverse change. Pollution can take the form of any substance (solid, liquid, or gas) or energy (such as radioactivity, heat, sound, or light). Pollutants, th ...

. Most of the islands were it breeds are covered by some degree of protection.

Global warming In common usage, climate change describes global warming—the ongoing increase in global average temperature—and its effects on Earth's climate system. Climate change in a broader sense also includes previous long-term changes to ...

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 Ocean acidification is the reduction in the pH value of the Earth’s ocean. Between 1751 and 2021, the average pH value of the ocean surface has decreased from approximately 8.25 to 8.14. The root cause of ocean acidification is carbon dioxid ...

may result in a decline of

crustacean Crustaceans (Crustacea, ) form a large, diverse arthropod taxon which includes such animals as decapoda, decapods, ostracoda, seed shrimp, branchiopoda, branchiopods, argulidae, fish lice, krill, remipedes, isopoda, isopods, barnacles, copepods, ...

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

External links

Species factsheet
- BirdLife International {{Taxonbar, from=Q1269924

ashy storm petrel The ashy storm petrel (''Hydrobates homochroa'') is a small, scarce seabird of the storm petrel family Hydrobatidae. It breeds colonially on islands off the coasts of California and Mexico, and is one of six species of storm petrel that live an ...

Birds of Mexico Native birds of the West Coast of the United States

Ashy storm petrel The ashy storm petrel (''Hydrobates homochroa'') is a small, scarce seabird of the storm petrel family Hydrobatidae. It breeds colonially on islands off the coasts of California and Mexico, and is one of six species of storm petrel that live an ...

Taxonomy

Description and ecology

Distribution, status, and threats

References

Further reading

External links