Data Zone
Justification of Red List category
This species is listed as Near Threatened because the global population decline is likely approaching 30% across three generations. If the decline is found to be larger, the species would qualify for uplisting.
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.
The species ranges from Baja California (Mexico) up the Pacific coast of the U.S.A. and Canada, through Alaska to the Aleutian Islands (U.S.A.) (del Hoyo et al. 1996). British Columbia (Canada) supports the largest population with approximately 2,700,000 breeding birds in the 1980s; it is estimated that there are approximately 600,000 birds in Alaska, 88,000 in Washington, 500 in Oregon, 131,000 in California and 20,000-40,000 in Baja California on the islands of San Benito, San Geronimo, Asuncion and San Roque (Nettleship 1996).
This species is found offshore and along sea coasts, mostly over the continental shelf to the edge, but also beyond into deep ocean. It feeds mostly on crustaceans throughout the year, supplemented by other invertebrates and small larval fish. The start of the breeding season varies greatly with latitude, from November in Baja California to possibly July in Alaska with laying typically timed to coincide with the spring zooplankton peaks (M. Hipfner in litt. 2020). The bird is known to double-brood, particularly in years characterised by high marine productivity (Johns et al. 2017). Birds form colonies from under 500 birds to over one million, usually at high densities on coastal islands with or without trees, and nesting on a wide range of habitats. It displays complex wintering patterns and whilst once thought to winter mainly offshore within the breeding range, with southerly populations being relatively sedentary compared to northern individuals which migrate south (del Hoyo et al. 1996), the species is now known to exhibit temporally and spatially variable migration patterns on an interannual basis. Tracking of individuals from British Colombia, Canada, the largest population of P. aleuticus individuals, illustrates both north (summer, fall) and south (fall, winter) migrations with distributions ranging from B.C. to the Aleutian Islands and Baja California at distances of 2757 and 3110 km respectively (Studholme et al. 2019). Migration behaviour also appears to be flexible, varying year-on-year in response to changeable oceanographic and environmental conditions, although some fixed migratory behaviour appears apparent (Studholme et al. 2019).
Introduced predators represent the most serious threat to Cassin’s Auklet colonies (Nettleship 1996, Rodway and Lemon 2011). House Rats Rattus rattus were introduced on Langara in the early 20th century (first noted in 1946), followed by Brown Rats R. norvegicus a few decades later (first noted in 1981) (Bertram and Nagorsen 1995). The auklet population on Langara and adjacent Cox and Lucy islands was extirpated by 1981 (Drent and Guiguet 1961, Rodway 1991) and only small numbers of auklets had recolonized Langara by 2004 (Regehr et al. 2007). Similarly, as House Rats invaded Anacapa, the local auklet population was completely or nearly extirpated between 1910 and 1975. After rat eradication, a total of 42 auklet nests in six discrete breeding areas were discovered between 2003 and 2012 (Whitworth et al. 2015). Recurring recolonization following rat eradication from the species's previous range indicate the substantial impact of rat predation on the species's distribution. Cats Felis catus were the likely driver of elimination or severe reductions, as it occurred in colonies from four Mexican islands (McChesney and Tershy 1998, Wolf et al. 2006). Raccoons Procyon lotor were introduced to the Queen Charlotte Islands in the early 1940s (which hold 18% of the world population of Cassin's Auklet), and two to four raccoons alone were responsible for up to 80% of observed predation on sub-adult and adult birds, while also depredating eggs and chicks (Hartman et al. 1997). Mink and raccoons are considered responsible for the extirpation of the once large colonies on Lanx and Cox Islands, Scott Archipelago in the 1930s (Hipfner et al. 2010). Further range expansion by raccoons in this region may pose a significant conservation threat to the seabird populations on the islands (Hartman and Eastman 1999).
Red Foxes Vulpes vulpes occur naturally on some near-shore islands along the Alaska Peninsula and on the Fox Islands in the eastern Aleutians. Following the release of foxes on more than 450 previously fox-free Alaskan islands, populations of nesting birds were severely reduced through increased predation levels on eggs, nestlings and adult birds (Bailey and Kaiser 1993). Currently, fox predation pressure may be alleviating, due to their removal from 39 islands of more than 500,000 ha. Further eradications are being planned for at least four more islands (Veitch and Clout 2002). Light pollution may cause disorientation of auklets and prolong the period of effective predation. Exceptionally bright lights used in the squid jigging fishery close to breeding colonies lead to greatly increased predation by Barn Owls Tyto alba and possibly Western Gulls Larus occidentalis, and may also cause collision mortality and discourage adults from returning to shore (Harfenist 2004).
In addition to predation pressures, the species's habitat is threatened by introduced herbivores which destroy and degrade nesting habitat by trampling nests, browsing native vegetation and increasing erosion of topsoil. Goats Capra hircus introduced to Guadalupe Island in the 1800s intensively trampled and browsed the nesting habitat of the Guadalupe Storm-petrel Oceanodroma macrodactyla, likely contributing to the apparent extinction of the species (Wolf et al. 2006). Considering the Cassin’s Auklets similar burrowing nesting habit, it is also at risk from habitat destruction by goats. Likewise, rabbits have been considered a threat due to habitat conversion and competition with burrowing birds. However, Hipfner et al. (2010) found similar vegetation changes on Triangle Island which hosts rabbits and the neighbouring rabbit-free Sartine Island. Although the driving mechanism is uncertain, the decrease in Tufted Hairgrass Deschampsia cespitosa cover at the expense of Salmonberry Rubus spectabilis poses a serious risk to the species, restricting the area of suitable nesting habitat.
The species is vulnerable to the effects of climate change, particularly changes in sea temperature regimes and coastal upwelling systems (Wolf et al. 2010). The frequency and magnitude of anomalous ocean conditions is expected to increase, threatening the long-term stability of some Cassin’s Auklet populations through decreased availability of krill and associated mortality and low recruitment; this particularly impacts auklets throughout the southern portion of its range, and those that winter in California, for whom krill comprises a major prey (Bertram et al. 2001, Hipfner 2008). Similarly. on Triangle Island, British Colombia, Canada, nesting success has been evidenced to be lower in warm-water years due to both the reduced abundance and, more importantly, earlier disappearance of the prey copepod Neocalanus cristatus. N. cristatus disappearance occurred on average 2-3 weeks earlier in warm-water years, reducing Auklet survival to, and weight at, fledging, thereby highlighting the significant impact of not just prey abundance, but also prey timing on predator survival as ocean conditions continue to warm (Hipfner 2008). Low breeding success has been documented in strong El Niño years (e.g., 1983, 1992, and 1997) (Manugian et al. 2015). During a 15-year study period (1994–2008), two extreme climate events (a strong El Niño event in 1997–1998 and an atmospheric blocking event in 2005) were both associated with a halving of the adult survival of female Cassin's Auklets (Morrison et al. 2011). Auklets have shown ability to respond adaptively to variation in oceanographic conditions and prey availability by modifying timing of breeding; however, in years when ocean conditions deteriorated after the initiation of breeding, prey availability was severely reduced beyond the birds’ potential for an adaptive response, resulting in diminished nestling growth and productivity (Abraham and Sydeman 2004, Manugian et al. 2015). Negative effects of climatic variation on both reproductive success and the survival of adult females is thought to be driving the ongoing decline in the Cassin's Auklet population on Triangle Island (Morrison et al. 2011). Likewise, the fluctuations in the northern Californian populations may be partially explained by anomalous warm-water conditions (Nettleship 1996), which are also thought to be responsible for the mass die-off of over 100,000 individuals reported from California to central British Columbia and Alaska through 2014 into January 2015 (Welch 2015, Devitt and Jardine 2016, Jones et al. 2018).
Oil pollution represents a significant threat and extractive operations may impact negatively on the species through increased pollution and collision with lights (Harfenist 2004). Past oil spills are known to have impacted the species. For example, in the 1986 Apex Houston oil spill, an estimated total of 10,577 birds were debilitated or killed (Page and Carter 1986, Page et al. 1990), including 'a smaller number' of Cassin's Auklets (Carter et al. 2003). Sub-lethal doses of petroleum have been found to reduce reproductive success in the species (Ainley et al. 1981). The species is also known to be exposed to varying degrees of plastic pollution although it is not yet clear whether exposure to such pollution is of significant impact to the species (Floren and Shugart 2017, O'Hara et al. 2019).
Declines have also been attributed to increases in numbers of native predators, including Bald Eagle Haliaeetus leucocephalus, Peregrine Falcon Falco peregrinus and Western Gull Larus occidentalis in some areas (Nettleship 1996). The Cassin’s Auklet was among the most common prey found in a Bald Eagle nest in California (23 out of 297 birds were of this species) (Erlandsson et al. 2007). Reports also include heavy predation by Western Gulls (Thoresen 1964, Manuwal 1979, Nelson 1989) and Peregrine Falcons, particularly on Triange Island where Auklets comprise the Peregrine's primary prey (Hipfner et al. 2011, M. Hipfner in litt. 2020). The seabird tick Ixodes uriae is also known to parasitise the species however, its influence appears minimal and doesn't seem influence P. aleuticus survival to fledging (Hipfner et al. 2019).
Human disturbance may also be contributing to reduced reproductive success in parts of the range. Birds whose burrows were closer to foodpaths or villages had a higher rate of nest abandonment and lower breeding success compared to birds nesting further away from settlements and passageways (Albores-Barajas and Soldatini 2011). Although chicks did not show any effect of disturbance in the early stages of growth, chicks in the experimentally disturbed groups stopped gaining weight sooner than undisturbed controls and fledged at lower weights (6 to 9% less) (Albores-Barajas et al. 2009).
Bycatch mortality of the species was recorded in the pelagic salmon driftnet fishery in the 1970s and 1980s (Ainley et al. 1981) and off British Columbia between 1995 and 2001 (Smith and Morgan 2005), but reduced fishing effort and greater fisheries restrictions have resulted in significant reductions in bycatch of Marbled Murrelet Brachyramphus marmoratus (caught in similar numbers to Cassin's Auklet in previous studies), and is no longer considered a driver of significant decline in that species (Zydelis et al. 2013). As such, it is unlikely that bycatch is impacting the Cassin's Auklet population at greater than a negligible rate.
Conservation and Research Actions Underway
The species, its eggs and nests are protected from hunting and collecting in the U.S.A. and Canada under the Migratory Birds Convention Act (Harfenist 2004). In 2002, a rat eradication programme was carried out on Ancapa Island, California. Within one year, Cassin's Auklets were recolonizing the island and between 2003 and 2012 a total of 42 nests were discovered (Whitworth et al. 2015). Rat eradication programmes have been carried out in other areas of the species's range, including Langara Island, British Columbia (Regehr et al. 2007). The designation of the Scott Islands Marine Wildlife Area (MWA) in British Colombia, Canada also aims to help protect foraging habitat for the species whilst also including plans to eradicate mink and raccoons from Lanz and Cox Islands to allow Auklets to recolonise both islands (Hipfner et al. 2011, M. Hipfner in litt. 2020) .
Conservation and Research Actions Proposed
Implement control programmes at breeding sites to remove invasive predators and problematic livestock (Nettleship 1996). Protect colonies from direct human disturbance. Restrict gill-net fishery operations close to colonies. Develop monitoring programmes to assess changes in population size and marine protected areas.
23 cm small, plump alcid. Short blackish/grey bill, base of lower mandible yellowish. Iris white, white crescent above eye. Dark greyish brown head with paler brown chin and throat. Upperparts blackish to slate grey with greyish brown breast and flanks, white belly. Legs and feet bluish pink, with black claws. No marked seasonal variation. Juvenile has whiter throat, browner wings and tail and dark brown iris (Nettleship 1996).
Text account compilers
Fjagesund, T., Everest, J., Martin, R.
Contributors
Ashpole, J, Butchart, S., Calvert, R., Carter, H., Ekstrom, J., Hipfner, M. & Miller, E.
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 23/12/2024.
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 23/12/2024.