Data Zone
Justification of Red List category
This species has a very small breeding range, with breeding restricted to two islets off Guadalupe Island, and potentially breeds on the mainland too. Invasive species are known to have had significant impacts on species on Guadalupe Island, and so if the species persists on the main island then the species is likely to be in continuing decline. Therefore, this newly-split species is precautionarily listed as Endangered.
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 for this taxon alone there may be 4,000 birds on Islote Negro and 3,000 on Islote Asfuera. Therefore, the overall population size may be best placed in the range 2,500-9,999 mature individuals.
Trend justification
The breeding populations on Islote Negro and Islote Afuera are assumed to be stable in the absence of evidence for any imminent threat. As the species potentially still breeds on Guadelupe, any remaining population there is likely affected by the predators present on the island and thus undergoing a continuing decline. Therefore, the species is precautionarily assessed as being in decline.
Hydrobates socorroensis is only known to breed from May/June to October/November on the islets of Islote Negro and Islote Afuera by Guadalupe Island, Mexico (Howell 2012). It may also breed on Guadalupe Island itself, but its persistence there is uncertain (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 California southward to the coast of Central America (Howell 2012).
The species's range over pelagic water is not well known, but it is assumed that it forages over a large area extending from California southward to the coast of Central America (Howell 2012). It feeds mainly on small fish, squid and crustaceans (Carboneras et al. 2018). It breeds in summer (May-October) on two 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 Ainsley's Storm-petrel (Hydrobates cheimomnestes), which breeds at the same sites during winter (November-April) (Howell 2012).
It is thought that Townsend’s Storm-petrel may exist locally on the main island of Guadalupe (Howell 2012). This population has likely suffered significant population declines in the past due to introduced species such as cats (thought to be the primary cause of the extinction of the Guadalupe Storm-petrel), goats (responsible for large-scale habitat degradation on Guadalupe, likely also trampling burrows) and potentially mice, present on Guadalupe (Aguirre-Muñoz et al. 2011) and known to depredate nests of the closely related Leach’s Storm-petrel (Bicknell et al. 2009). However, goats were eradicated in the mid-2000s (Aguirre-Muñoz et al. 2011) and although cats are still present on the island, they are controlled around seabird nesting sites (Aguirre-Muñoz et al. 2011), likely reducing the extend of predation. Further, the islets on which Townsend's Storm-petrel breeds are thought to be free of invasive species. Although little research currently takes place on the islets surrounding Guadalupe, it has been shown that disturbance by investigators can have significant negative impacts on the breeding success of the closely related Leach's Storm-petrel (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 islets. Investigate the pelagic distribution range. Monitor the population trend.
Text account compilers
Stuart, A., Martin, R., Hermes, C., Westrip, J., Fjagesund, T.
Recommended citation
BirdLife International (2024) Species factsheet: Townsend's Storm-petrel Hydrobates socorroensis. Downloaded from
https://datazone.birdlife.org/species/factsheet/townsends-storm-petrel-hydrobates-socorroensis on 22/12/2024.
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 22/12/2024.