• Summary
• Text account
• Data table and detailed info
• Distribution map
• Reference and further resources

Taxonomic note
Hydrobates leucorhous (del Hoyo and Collar 2014) has been split into H. leucorhous, H. socorroensis and H. cheimomnestes (which see) (Handbook of the Birds of the World and BirdLife International 2018), based on the proposal of Howell (2012).

Taxonomic source(s)
del Hoyo, J., Collar, N.J., Christie, D.A., Elliott, A. and Fishpool, L.D.C. 2014. HBW and BirdLife International Illustrated Checklist of the Birds of the World. Volume 1: Non-passerines. Lynx Edicions BirdLife International, Barcelona, Spain and Cambridge, UK.
Handbook of the Birds of the World and BirdLife International. 2018. Handbook of the Birds of the World and BirdLife International digital checklist of the birds of the world. Version 3. Available at: https://datazone.birdlife.org/userfiles/file/Species/Taxonomy/HBW-BirdLife_Checklist_v3_Nov18.zip.
Howell, N. G. 2012. Petrels, Albatrosses, and Storm-Petrels of North America: A Photographic Guide. Princeton University Press, Princeton, New Jersey, USA.

Red List criteria met

Critically Endangered	Endangered	Vulnerable
-	B2ab(v)	B2ab(v); C2a(ii); D2

Red List history

Year	Category	Criteria
2018	Endangered	B2ab(v)
2016	Not Recognised
2012	Not Recognised
2008	Not Recognised
2004	Not Recognised
2000	Not Recognised
1994	Not Recognised
1988	Not Recognised

Migratory status	full migrant	Forest dependency	does not normally occur in forest
Land-mass type		Average mass	37 g

	Estimate	Data quality
Extent of Occurrence (breeding/resident)	4,950,000 km2	medium
Area of Occupancy (breeding/resident)	12 km2
Number of locations	3	-
Severely fragmented?	no	-

	Estimate	Data quality	Derivation	Year of estimate
Population size	2500-9999 mature individuals	medium	estimated	2012
Population trend	decreasing	-	inferred	1997-2036
Generation length	13 years	-	-	-
Number of subpopulations	1	-	-	-
Percentage of mature individuals in largest subpopulation	100%	-	-	-

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.

Country/Territory	Presence	Origin	Resident	Breeding visitor	Non-breeding visitor	Passage migrant
Mexico	extant	native		yes
USA	extant	native

Country/Territory	IBA Name

Habitat (level 1)	Habitat (level 2)	Importance	Occurrence
Marine Coastal/Supratidal	Sea Cliffs and Rocky Offshore Islands	major	breeding
Marine Intertidal	Rocky Shoreline	major	breeding
Marine Neritic	Pelagic	major	non-breeding
Marine Neritic	Pelagic	major	breeding
Marine Oceanic	Epipelagic (0-200m)	major	non-breeding
Marine Oceanic	Epipelagic (0-200m)	major	breeding
Altitude		Occasional altitudinal limits

Threat (level 1)	Threat (level 2)	Impact and Stresses
Human intrusions & disturbance	Work & other activities	Timing		Scope		Severity		Impact
		Unknown		Minority (<50%)		Negligible declines		Unknown
		Stresses Species disturbance, Reduced reproductive success
Invasive and other problematic species, genes & diseases	Invasive non-native/alien species/diseases - Felis catus	Timing		Scope		Severity		Impact
		Ongoing		Unknown		Negligible declines		Unknown
		Stresses Reduced reproductive success, Species mortality
Invasive and other problematic species, genes & diseases	Invasive non-native/alien species/diseases - Mus musculus	Timing		Scope		Severity		Impact
		Past, Unlikely to Return		Majority (50-90%)		Slow, Significant Declines		Past Impact
		Stresses Reduced reproductive success
Invasive and other problematic species, genes & diseases	Invasive non-native/alien species/diseases - Unspecified species	Timing		Scope		Severity		Impact
		Past, Unlikely to Return		Majority (50-90%)		Rapid Declines		Past Impact
		Stresses Ecosystem degradation, Reduced reproductive success, Species mortality

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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.