Data Zone
Justification of Red List category
This species has an extremely large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). Despite the fact that the population trend appears to be decreasing, the decline is not believed to be sufficiently rapid to approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is extremely large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
Population justification
The global population is estimated to number 20 million mature individuals (Partners in Flight 2019).
Trend justification
The population is suspected to be in decline due to predation by invasive species and loss of access to prey resources due to climate change-driven trophic shifts.
The Least Auklet can be found in the northern Pacific Ocean. It ranges from Hokkaido (Japan) and south-west Alaska (U.S.A.) up to the south of the Chukchi Sea. It breeds on the islands and the coast of Siberia (Russia) and Alaska (del Hoyo et al. 1996).
This marine species is found offshore and along coasts. It forages on planktonic crustaceans near-shore or offshore throughout the year, almost always in large flocks and in the open oceans, where plankton densities are high. Birds arrive at colonies in the spring, earliest towards the extreme south and latest in the north. It is monogamous with shared mate choice and relatively low mate fidelity between years. Colonies of more than one million individuals may form on remote islands and along the coasts. Nesting takes place on talus slopes, beach boulder rubble, sea cliffs and lava fields, where crevices are suitable for breeding (del Hoyo et al. 1996).
Invasive species and future climate change pose potential threats to the species. In 2007, on Sirius Point, Kiska Island, Brown Rat Rattus norvegicus abundance was qualitatively the lowest, and Least Auklet productivity the highest on record since 2001, suggesting that rats are limiting auklet breeding success (Bond and Jones 2007). There appears to be a critical threshold of rat abundance, above which reproductive failure ensues, and below which auklets are able to buffer the effects of rats on reproductive success. The Sirius Point colony suffered complete reproductive failure in 2001 and 2002, which were also the years with the highest recorded rat abundance. On St. Paul and St. George Island, Red Foxes Vulpes vulpes may be the single largest source of auklet mortality (Roby and Brink 1986, Jones 1992).
The species is sensitive to the possible effects of climate change, including the timing of ice-retreat and altered prey distribution and abundance. As yet, interannual variation in prey species availability appears to be the most important factor determining productivity of auklets (Sheffield Guy et al. 2009). Dorresteijn et al. (2012) found that the species experienced higher nutritional stress during warm years compared to cold years. The vital influx of prey-bearing water masses and retention time of preferred prey items (oceanic copepods) on the shelf are controlled by physical processes (winter sea ice cover, timing of ice retreat and flow through the Bering Strait) which are predicted to be altered by future climate change, most likely with negative effects on the Least Auklet population (Dorresteijn et al. 2012).
Text account compilers
Hermes, C.
Contributors
Butchart, S., Calvert, R., Ekstrom, J., Fjagesund, T., Miller, E. & Martin, R.
Recommended citation
BirdLife International (2024) Species factsheet: Least Auklet Aethia pusilla. Downloaded from
https://datazone.birdlife.org/species/factsheet/least-auklet-aethia-pusilla 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.