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Ashy Storm-petrel

Hydrobates homochroa


This nocturnal storm-petrel is notoriously difficult to identify due to its all dark plumage, which is hard to pick out in the dark.

They tend to come and go from their rocky island nesting sites at night, likely to avoid predators. Identification issues and difficulty in locating hidden nests has meant that little research has been undertaken on the Ashy Storm-petrel. Unlike most species of storm-petrel, they do not venture very far from their breeding island. They are found only on offshore islands of Baja California in Mexico and California in the USA. Introduced predators, such as feral cats and rats, are a threat to birds at the nesting grounds, feeding on young chicks and eggs. At sea, pollution from oil and organochlorides affect numbers. The impact of bright lights from fishing vessels, other ocean-going vessels, and offshore energy platforms is yet to be understood, but this could be a key factor in the decline of this nocturnal species.

  • Order: Procellariiformes
  • Family: Hydrobatidae
  • Population: 5,200-10,000
  • Trend: decreasing
  • Size: 19cm

EDGE Score

EDGE Score: 5.16 (?)
ED Score: 20.83 (?)
GE / IUCN Red List (?)
Not Evaluated Data Deficient Least Concern Near Threatened Vulnerable Endangered Critically Endangered Extinct in the Wild Extinct


This species nests on several islands off the coast of California in the USA and northern Mexico. A pelagic bird, this storm-petrel spends much its time over waters in this region.

Habitat and Ecology

This species is usually found out on the open ocean, and nests on rocky island terrain. They are social birds, nesting in small and large colonies on offshore islands. The birds’ diet is comprised of spiny lobster larvae and other crustaceans, larval fish, and squid. The breeding season is very long and typically lasts from February to January of the following year. Typically the monogamous pair produces one egg.

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This wordcloud illustrates the threats facing this species. The size of each word indicates the extent of a species range that is affected by that threat (larger size means a greater area is affected). The colour of the word indicates how much that threat impacts the species (darker shades of red mean the threat is more severe).

Habitat change Fishing Recreation Invasive species Native species Industry Agriculture Energy

Threat wordcloud key:

Small area affected
Large area affected
Least severe
Most severe
Severity unknown
Source: The IUCN List of Threatened Species. Version 2017.1.
Available at:

Download the Survival Blueprint for this species below. Each survival blueprint is compiled by an EDGE Fellow working on the species with input from collaborators and stakeholders. The Survival Blueprint provides a status review (information on the distribution, protection status, habitat & ecology, threat and stakeholder analysis) and more information on the action programme listed here.  

Vision (30-50 years)

The population of ASSP is stable through reducing the threats to the species conservation

Goal (5-10 years)

Prevent the decline of the ASSP in all the breeding sites by mitigating the population size limiting factors


Reduce the predation of ASSP by invasive mammals in breeding sites Critical
Evaluate population trends along its range-wide distribution Critical
Prevent the introduction or reintroduction of invasive mammals to breeding sites High
Reduce the predation by native species that became problematic High
Increase suitable habitat for the species High
Reduce the human disturbance in breeding sites Medium
Assess at-sea threats Medium
Prevent the damage of ASSP caused by oil spills Low
Fill information gaps that aid in conservation management Low

Alejandra Fabila Blanco

  • Project name: Conserving the endangered Ashy Storm-Petrel in Mexico.
  • Project site: Todos Santos Islands, Mexico
  • Active: 2021 - ongoing
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