Data Zone
Justification of Red List category
This species occurs on only three islets, with invasive species posing a severe future threat that could drive the species to Critically Endangered or Extinct in a very short period of time. Therefore, it is assessed here as Vulnerable.
Population justification
In Brooke (2004), the population size for both H. cheimomnestes and H. socorroensis combined was placed at 5,000 pairs (i.e. 10,000 mature individuals). Howell (2012) suggests that the population for this taxon alone is likely no more than a few thousand individuals. Therefore, the population size may be best placed in the range 2,500-9,999 mature individuals.
Trend justification
It is not certain whether invasives, which have impacted species on mainland Guadalupe Island, have made it to the offshore islets, and so their direct impact on the species is uncertain. It is not known whether potential at sea threats have any impact on this species either. Therefore, in the absence of any evidence for any declines the species is tentatively assessed as being stable.
Hydrobates cheimomnestes is only known to breed from November/December to April/May on the islets of Islote Negro, Islote Afuera and Gargoyle Rock by Guadalupe Island, Mexico (Howell 2012). The pelagic distribution of the species is not well known; it is assumed that during the non-breeding season the species ranges from the Baja California Peninsula southward to the Galapagos Islands (Howell 2012, Carboneras et al. 2018).
The species's range over pelagic water is not well known, but it is assumed that it forages over a large area extending from Guadalupe Island southward to Galapagos (Howell 2012). It feeds mainly on small fish, squid and crustaceans (Carboneras et al. 2018). It breeds in winter (November-April) on three islets nearby Guadalupe islands (Carboneras et al. 2018). Nests are placed in crevices and burrows (Howell 2012). The species is temporally segregated from the co-occurring Townsend's Storm-petrel Hydrobates socorroensis, which breeds at the same sites during summer (May-October) (Howell 2012).
It is likely that a population of Ainley’s Storm-petrel previously existed on Guadalupe island, but was extirpated following the introduction of cats and goats to the main island through predation and trampling of burrows (Aguirre-Muñoz et al. 2011). Mice also occur on Guadalupe (Aguirre-Muñoz et al. 2011) and are a known nest predator of other petrels (Bicknel et al. 2009). However, there are no invasive species known on the three small islets off Guadalupe on which Ainley’s Storm-petrel is currently breeding. Although little research currently takes place on the islets surrounding Guadalupe, it has been shown that disturbance by investigators have significant negative impacts on the breeding success of the closely related Leach's Storm-petrel Hydrobates leucorhous (Blackmer et al. 2004) and thus should be considered a potential threat.
Conservation Actions Underway
None known.
Conservation Actions Proposed
Continue biocontrol to avoid the spread of invasive predators to the islands. Investigate the pelagic distribution range. Monitor the population trend.
c.19 cm. Medium-sized Storm-petrel with dark brown plumage and a distinct white patch on the rump; tail forked or deeply notched.
Text account compilers
Martin, R., Fjagesund, T., Stuart, A., Hermes, C., Westrip, J.
Recommended citation
BirdLife International (2024) Species factsheet: Ainley's Storm-petrel Hydrobates cheimomnestes. Downloaded from
https://datazone.birdlife.org/species/factsheet/ainleys-storm-petrel-hydrobates-cheimomnestes on 21/12/2024.
Recommended citation for factsheets for more than one species: BirdLife International (2024) IUCN Red List for birds. Downloaded from
https://datazone.birdlife.org/species/search on 21/12/2024.