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

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.

Red List criteria met

Critically Endangered	Endangered	Vulnerable
-	-	-

Red List history

Year	Category	Criteria
2020	Near Threatened	A2abce+3bce+4abce
2018	Near Threatened	A2b+3b+4b
2016	Near Threatened	A2b+3b+4b
2015	Near Threatened	A2b+3b+4b
2012	Least Concern
2009	Least Concern
2008	Least Concern
2004	Least Concern
2000	Lower Risk/Least Concern
1994	Lower Risk/Least Concern
1988	Lower Risk/Least Concern

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

	Estimate	Data quality
Extent of Occurrence (breeding/resident)	8,620,000 km2	medium
Extent of Occurrence (non-breeding)	12,100,000 km2	medium
Severely fragmented?	no	-

	Estimate	Data quality	Derivation	Year of estimate
Population size	3600000 mature individuals	poor	estimated	2009
Population trend	decreasing	-	estimated	2003-2024
Rate of change over the past 10 years/3 generations (longer of the two periods)	20-29%	-	-	-
Rate of change over the future 10 years/3 generations (longer of the two periods)	20-29%	-	-	-
Rate of change over the past & future 10 years/3 generations (longer of the two periods)	20-29%	-	-	-
Generation length	6.94 years	-	-	-

Population justification: The total population is estimated to be at least 3,600,000 breeding birds (Nettleship 1996), which equates to approximately 5,400,000 individuals.

Trend justification: In North America, this species has undergone a large and statistically significant decrease over the last 40 years (Butcher and Niven 2007). A study by Rodway and Lemon (2011) found declines in monitored burrows at several colonies in British Columbia and estimated a 40% decline in monitored burrows over 20 years between 1989 and 2009 in the largest known breeding population on Triangle Island (part of the Scott Islands). Declines appear to have begun in c.1990. If the declines on Triangle Island are representative of the whole Scott Islands population, there could have been a total loss of approximately 800,000 birds in the region, or >20% of the world breeding population. Large-scale declines have also been documented on the South Farallon Islands, California (H. Carter in litt. 2013) whilst the Christmas Bird Count currently estimates USA-wide declines at rates of ~1.42% per year, or ~25.75% across three generations (Meehan et al. 2018). The overall rate of decline is currently placed in the band 20-29% in three generations, but confirmation that declines similar to those seen at Triangle Island, British Colombia and the South Farallon Islands, California are taking place across the whole range would lead to the overall rate of decline being increased.

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

Country/Territory	IBA Name
Canada	Anthony Island
Canada	Englefield Bay Islands
Canada	Frederick Island
Canada	Hippa Island
Canada	Kerouard and St. James Islands
Canada	Moore and Byers Islands and Banks
Canada	Ramsay and Northern Juan Perez Sound Islands
Canada	Rankine and Langtry Islands
Canada	Scott Island Group
Canada	Skincuttle Inlet Islands
Canada	Solander Island and Brooks Bay
Mexico	Bahía Todos Santos
Mexico	Isla Asunción
Mexico	Isla San Roque
Mexico	Islas San Benito
USA	Amagat & Umga Island Colonies
USA	Castle Rock Colonies
USA	Cherni Island Complex Colonies
USA	Forrester Island Colonies
USA	Gulf of Alaska Shelf 155W57N
USA	Olympic Continental Shelf

Habitat (level 1)	Habitat (level 2)	Importance	Occurrence
Marine Coastal/Supratidal	Sea Cliffs and Rocky Offshore Islands	major	breeding
Marine Neritic	Macroalgal/Kelp	major	resident
Marine Neritic	Pelagic	major	resident
Marine Neritic	Seagrass (Submerged)	major	resident
Marine Neritic	Subtidal Loose Rock/pebble/gravel	major	resident
Marine Neritic	Subtidal Rock and Rocky Reefs	major	resident
Marine Neritic	Subtidal Sandy	major	resident
Marine Neritic	Subtidal Sandy-Mud	major	resident
Marine Oceanic	Epipelagic (0-200m)	suitable	resident
Marine Oceanic	Mesopelagic (200-1000m)	suitable	resident
Altitude	0 - 100 m	Occasional altitudinal limits

Threat (level 1)	Threat (level 2)	Impact and Stresses
Biological resource use	Fishing & harvesting aquatic resources - Unintentional effects: (large scale) [harvest]	Timing		Scope		Severity		Impact
		Ongoing		Majority (50-90%)		Negligible declines		Low Impact: 5
		Stresses Species mortality
Climate change & severe weather	Temperature extremes	Timing		Scope		Severity		Impact
		Ongoing		Majority (50-90%)		Causing/Could cause fluctuations		Medium Impact: 6
		Stresses Indirect ecosystem effects, Reduced reproductive success, Species mortality
Human intrusions & disturbance	Recreational activities	Timing		Scope		Severity		Impact
		Ongoing		Majority (50-90%)		Slow, Significant Declines		Medium Impact: 6
		Stresses Species disturbance, Reduced reproductive success
Invasive and other problematic species, genes & diseases	Invasive non-native/alien species/diseases - Capra hircus	Timing		Scope		Severity		Impact
		Ongoing		Majority (50-90%)		Slow, Significant Declines		Medium Impact: 6
		Stresses Species disturbance, Ecosystem degradation, Reduced reproductive success
Invasive and other problematic species, genes & diseases	Invasive non-native/alien species/diseases - Felis catus	Timing		Scope		Severity		Impact
		Ongoing		Majority (50-90%)		Slow, Significant Declines		Medium Impact: 6
		Stresses Species mortality
Invasive and other problematic species, genes & diseases	Invasive non-native/alien species/diseases - Oryctolagus cuniculus	Timing		Scope		Severity		Impact
		Ongoing		Minority (<50%)		Negligible declines		Low Impact: 4
		Stresses Ecosystem degradation, Reduced reproductive success
Invasive and other problematic species, genes & diseases	Invasive non-native/alien species/diseases - Procyon lotor	Timing		Scope		Severity		Impact
		Ongoing		Minority (<50%)		Slow, Significant Declines		Low Impact: 5
		Stresses Species mortality
Invasive and other problematic species, genes & diseases	Invasive non-native/alien species/diseases - Rattus norvegicus	Timing		Scope		Severity		Impact
		Ongoing		Majority (50-90%)		Slow, Significant Declines		Medium Impact: 6
		Stresses Reduced reproductive success, Species mortality
Invasive and other problematic species, genes & diseases	Invasive non-native/alien species/diseases - Rattus rattus	Timing		Scope		Severity		Impact
		Ongoing		Majority (50-90%)		Slow, Significant Declines		Medium Impact: 6
		Stresses Reduced reproductive success, Species mortality
Invasive and other problematic species, genes & diseases	Invasive non-native/alien species/diseases - Vulpes vulpes	Timing		Scope		Severity		Impact
		Ongoing		Minority (<50%)		Slow, Significant Declines		Low Impact: 5
		Stresses Reduced reproductive success, Species mortality
Invasive and other problematic species, genes & diseases	Problematic native species/diseases - Falco peregrinus	Timing		Scope		Severity		Impact
		Ongoing		Minority (<50%)		Negligible declines		Low Impact: 4
		Stresses Species mortality
Invasive and other problematic species, genes & diseases	Problematic native species/diseases - Haliaeetus leucocephalus	Timing		Scope		Severity		Impact
		Ongoing		Minority (<50%)		Slow, Significant Declines		Low Impact: 5
		Stresses Species mortality
Invasive and other problematic species, genes & diseases	Problematic native species/diseases - Larus occidentalis	Timing		Scope		Severity		Impact
		Ongoing		Minority (<50%)		Slow, Significant Declines		Low Impact: 5
		Stresses Species mortality
Pollution	Excess energy - Light pollution	Timing		Scope		Severity		Impact
		Ongoing		Minority (<50%)		Slow, Significant Declines		Low Impact: 5
		Stresses Species mortality
Pollution	Industrial & military effluents - Oil spills	Timing		Scope		Severity		Impact
		Ongoing		Majority (50-90%)		Slow, Significant Declines		Medium Impact: 6
		Stresses Ecosystem degradation, Reduced reproductive success, Species mortality

Purpose	Scale
Food - human	subsistence, national

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Recommended citation
BirdLife International (2024) Species factsheet: Cassin's Auklet Ptychoramphus aleuticus. Downloaded from https://datazone.birdlife.org/species/factsheet/cassins-auklet-ptychoramphus-aleuticus on 23/11/2024.
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 23/11/2024.