CDC Logo

BC Conservation Data Centre: Conservation Status Report

Ptychoramphus aleuticus
Cassin's Auklet

Scientific Name: Ptychoramphus aleuticus
English Name: Cassin's Auklet
Provincial Status Summary
Status: S2B,S3N
Date Status Assigned: April 28, 2018
Date Last Reviewed: April 28, 2018
Reasons: There are estimated to be 62 colonies, however, the majority of the population is restricted to one island and many of the other islands are threatened by raccoon and/or rat predation. The species shows high sensitivity to conditions at sea associated with climate change. As colonial nesters, they are susceptible to catastrophic events such as oil spills.
Range Extent: F = 20,000-200,000 square km
Range Extent Estimate (km2): 67,100 km2
Range Extent Comments: Approx 67,100 km2 - minium convex polygon encompassing known extant colonies in B.C. (COSEWIC 2014)
Breeds on 62 offshore islands, off the west and north coasts of Vancouver Island, locally along the central mainland coast and throughout much of coastal Haida Gwaii (COSEWIC 2014, Rodway et al. 2016). Note that this does not include the species' marine range which is much more extensive.
Area of Occupancy (km2): E = 26-125
Area of Occupancy Estimate (km2): 62 colonies + 1 extra grid cell
Area of Occupancy Comments: Index of area of occupancy = 228 km2, encompassing the 62 colonies plus one extra grid cell to encompass the large Triangle Island colony (COSEWIC 2014). Again, this does not include the marine range which is much more extensive.
Occurrences & Population
Number of Occurrences: C = 21 - 80
Comments: There are an estimated 62 breeding colonies based on the latest survey information, but approximately 70% of population (1,095,274 +/- 51,496 breeding individuals; 1989 survey) is concentrated in the Triangle Island colony (Rodway 1991, COSEWIC 2014, Rodway et al. 2016).
Number of Occurrences with Good Viability / Ecological Integrity: D = 13 - 40
Comments: There are 29 colonies in B.C. supporting 1000 or more breeding birds (500 pairs) with no imminent threats from rats or raccoons (COSEWIC 2014). The recent extirpation due to river otter predation of the Seabird Rocks colony (estimated to support 269 pairs in 1988; Carter et al. 2012) indicates that smaller colonies are vulnerable to extirpation.
Number of Occurrences Appropriately Protected & Managed: E = >40
Comments: Most colonies are in national parks (24), Haida Gwaii Heritage sites and conservancies (24), ecological reserves (19), provinicial parks (2) or Wildlife Management Areas (3), with only one small colony (Egg Island, estimated 10 breeding birds) lacking protection (COSEWIC 2014). On the other hand there is virtually no protection for marine foraging areas where the birds spend most of their lives and are currently experiencing  severe negative impacts and potential threats.
Population Size: GH = 100,000 to >1,000,000 individuals
Comments: Estimated at 2.7 million birds based on 1980s surveys (Rodway 1991), representing 75% of world population, but breeding populations in the California Current system have declined by about 30% since 1980s (inferred from 40% decline in number of occupied burrows in Triangle Island colony; COSEWIC 2014). Population in 2018 likely around 1.5-2.5 million birds, including non-breeding and immatures at sea.
Threats (to population, occurrences, or area affected)
Degree of Threat: A = Very high
Comments: Three major threats: (i) impacts of climate change affecting prey quantity, quality and access, (ii) predation by introduced rats and raccoons on several colonies, and (iii) marine oil spills. The significance of these threats to population stability in B.C. as a whole is not yet fully evaluated.
Several recent studies show this species to be highly vulnerable to effects of climate change (warming oceans, increased frequency of El Niņo and large-scale sea-surface temperature anomalies) affecting the quantity, quality and timing of occurrence of preferred prey. These effects impact both breeding productivity and the survival of breeding and non-breeding birds (Gaston et al. 2009, Ainley et al. 2011, COSEWIC 2014, Jones et al. 2018). Climate change is also a possible factor driving changes in vegetation cover at the major Triangle Island colony, reducing the favoured Tufted Hairgrass habitat (Hipfner et al. 2010).
Introduced rats, raccoons and mink are present on 16 colonies and have caused extirpations or significant delines at 9 colonies (COSEWIC 2014). Rats have recently been eradicated at 3 colonies but could re-invade Langara Island from fishing lodges there. Raccoons could reach additional colonies unless controlled. Fortunately the biggest colony at Triangle Island is not currently affected by introduced predators.
The species is also highly susceptible to both catastrophic and chronic oil spills at sea  (Burger 1992, Ainley et al. 2011). A single large spill near the Scott Islands off northern Vancouver Island could affect about half of the global breeding population. Shipping is expected to increase off BC and in areas to the south where the BC population over-winters, with concomittant risks of oil spills, especially if the Trans-Mountain Pipeline to Burnaby is constructed.
Other, less pervasive, threats include pollution from industrial chemicals (e.g., fire-retardants), ingestion of micro-plastics in zooplankton prey, increased frequency of toxic algal blooms at sea, and disturbance by recreational visitors at colonies (Ainley et al. 2011, COSEWIC 2013).
Restoration of populations where the species has been heavily impacted may be difficult as the species is highly philopatric and some populations to the south of B.C. are declining too (Ainley et al. 2011).
Trend (in population, range, area occupied, and/or condition of occurrences)
Short-Term Trend: E = Decline of 30-50%
Comments: Using the data given by COSEWIC (2014), i.e., that 75% of the BC population breeds within the California Current system where the largest colony (Triangle Island) showed declines of -2.45%/year over 15 years (Gaston et al. 2009, 2016), and that generation time is 7 years, and assuming that breeders in the Alaska Current system have stable populations (ignoring the continued impacts of rats and raccoons), then the total BC breeding population will have declined by 30.45% over 21 years (3 generations). Recent research provides evidence of continued and severe impacts of climate change, warming ocean and abnormal marine heat waves on the survival and recruitment of Cassin's Auklets breeding in the California Current system (Gaston et al. 2009, Ainley et al. 2011, Bertram et al. 2017, Jones et al. 2018).
Long-Term Trend: AC = Decline of >70%
Comments: If the estimated current rate of decline for BC breeders (30.45% over 21 years; approx. -1.84% per year) continues unchanged it will take 65 years for the population to decline by 70%. Note that there is huge uncertainty in this crude estimate - declines in the California Current system could be offset by increases in colonies within the Alaska Current system and by continued eradication and control of introduced mammals in Haida Gwaii and the Scott Islands.
Other Factors
Intrinsic Vulnerability: AB=Highly to moderately vulnerable.
Comments: Research shows that the species is highly vulnerable to the marine effects of climate change, to introduced predators and to marine oil spills.
Environmental Specificity: B=Narrow. Specialist or community with key requirements common.
Comments: Cassin's Auklets recently shown to be dependent on concentrations of high-lipid zooplankton and also have fairly specific requirements for the location, topography and vegetation cover of breeding colonies.
Other Rank Considerations: British Columbia supports about 75% of the global breeding population of Cassin's Auklets, placing high responsibility for protection within the province.
Information Gaps
Research Needs: Additional research is needed on the long-term impacts of climate change, especially as it affects the quantity, quality and availability of preferred zooplankton prey and the impacts of severe storms. We need to know whether reductions at colonies within the California Current system might be offset by increases at colonies within the Alaska Current system (i.e., Haida Gwaii). Further research is required into effective measures for the control or eradication of introduced rats, raccoons and mink. More information is also required on the significance of mortality associated with gillnet fisheries and potential impacts of offshore wind turbines.
Inventory Needs: Colonies should be monitored on a regular basis (at least every 5 years) to determine trends in population and reproductive success. Most  colonies have not been censused since the 1980s. Updated information on the largest colonies with >100,000 birds (Triangle, Frederick, Kerouard, Beresford, Sartine) is especially urgent. The presence/absence of introduced predators at nesting colonies should also be monitored on a regular basis.
Protection: The efficacy and implementation of Marine Protected Areas covering major foraging zones needs to be rigorously investigated. Routing of major shipping lanes affecting known foraging concentrations (year-round) should be reviewed. Protection measures, appropriate forestry practices and General Wildlife Measures within the BC Identified Wildlife Management Strategy (BC Government 2004) should be made available to resource managers where breeding colonies might be affected by forestry.
Management: Control of mammalian predators (rats, raccoons and mink) on nesting islands is the highest priority. They should be removed from all colonies (including those with extirpations), and measures should be developed to prevent the introduction of rats and raccoons to other colonies. Marine oil spill response plans should be evaluated and amended as necessary to address the needs of Cassin's Auklet populations. Guidelines and control measures for visitation of seabird colonies should be developed and enforced.
Author: A. Burger, L. Ramsay, B. Niedzielski
Date: February 15, 2018
Burger, A.E. 1992. The effects of oil pollution on seabirds off the west coast of Vancouver Island. Pages 120-128 in K.Vermeer, R.W. Butler, and K.H. Morgan, eds. The ecology, status, and conservation of marine and shoreline birds on the west coast of Vancouver Island. Can. Wildl. Serv. Occ. Pap. No. 75.
Campbell, R.W., N.K. Dawe, I. McTaggart-Cowan, J.M. Cooper, G.W. Kaiser, and M.C.E. McNall. 1990b. The Birds of British Columbia Vol. 2: Nonpasserines: Diurnal Birds of Prey through Woodpeckers. Royal British Columbia Museum, Victoria, BC.
Cannings, R.J. 1998. The Birds of British Columbia - a taxonomic catalogue. B.C. Minist. Environ., Lands and Parks, Wildl. Branch, Victoria, Wildl. Bull. B-86. 266pp.
Hartman, L.H. 1993. Ecology of coastal raccoons (Procyon lotor) on the Queen Charlotte Islands, British Columbia, and evaluation of their potential impact on native burrow-nesting seabirds. M.Sc. Thesis, Univ. Victoria, Victoria, BC.
Manuwal, C.D. 1972. The population ecology of Cassin's Auklets on southeast Farallon Island, California. Unpubl. Ph.D. Thesis, Univ. California, Los Angeles, CA.
Manuwal, C.D. 1974. Effects of territoriality on breeding in a population of Cassin's Auklets. Ecology 55:1399-1406.
Manuwal, D.A., and A.C. Thoresen. 1993. Cassin's Auklet (Ptychoramphus aleuticus). No. 50 in A. Poole, and F. Gill, eds. The Birds of North America. Acad. Nat. Sci., Philadelphia; Am. Ornithol. Union, Washington, D.C.
Rodway, M.S. 1991. Status and conservation of breeding seabirds in British Columbia. Pages 43-102 in J.P. Croxall, ed. Seabird status and conservation: a supplement. Int. Counc. for Bird Preservation Tech. Publ. No. 11. Cambridge. U.K.
Springer, A., A. Kondratyev, H. Ogi, Y. Shibaev, and G. van Vliet. 1993. Status, ecology and conservation of Synthliboramphus murrelets and auklets. Pages 187-200 in K. Vermeer, K. Briggs, K. Morgan, and D. Siegel-Causey, eds. The status, ecology and conservation of marine birds of the North Pacific. Can. Wildl. Serv. Spec. Publ., Ottawa.
Vermeer, C. 1987. Growth and nesting periods of Cassin's Auklets: adaptations of planktivorous auklets to breed at northern latitudes. Can. Tech. Rep. Hydrology Ocean Sci. No. 93. Inst. Ocean Sci., Sidney, BC.
Vermeer, C., and M. Lemon. 1986. Nesting habits and habitats of Ancient Murrelets and Cassin's Auklets in the Queen Charlotte Islands, British Columbia. Murrelet 67:33-44.
Vermeer, K., and S.G. Sealy. 1984. Status of the nesting seabirds of British Columbia. Pp. 29-40 in Croxall et al., eds. Status and conservation of the world's seabirds. ICBP Tech. Publ. No. 2.

Please visit the website Conservation Status Ranks for information on how the CDC determines conservation status ranks. For global conservation status reports and ranks, please visit the NatureServe website

Suggested Citation:

B.C. Conservation Data Centre. 2018. Conservation Status Report: Ptychoramphus aleuticus. B.C. Minist. of Environment. Available: (accessed Feb 6, 2023).