Species

Justification
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.

Taxonomic source(s)
AOU. 1998. Check-list of North American birds. American Ornithologists' Union, Washington, D.C.
Sibley, C. G.; Monroe, B. L. 1990. Distribution and taxonomy of birds of the world. Yale University Press, New Haven, USA.
Stotz, D. F.; Fitzpatrick, J. W.; Parker, T. A.; Moskovits, D. K. 1996. Neotropical birds: ecology and conservation. University of Chicago Press, Chicago.

Distribution and population
Cassin's Auklet ranges from Baja California (Mexico) up the Pacific coast of the USA and Canada, through Alaska to the Aleutian Islands (USA) (del Hoyo et al. 1996).

Trend justification
This species has undergone a large and statistically significant decrease over the last 40 years in North America (-96.8% decline over 40 years, equating to a -57.9% decline per decade; data from Breeding Bird Survey and/or Christmas Bird Count: Butcher and Niven 2007). Note, however, that these surveys cover less than 50% of the species's range in North America.

Ecology
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 invetebrates and small larval fish. The start of the breeding season varies greatly with latitude, from November in Baja California to July in Alaska. 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 winters mainly offshore within the breeding range, with southerly populations being relatively sedentary compared to northern individuals which migrate south (del Hoyo et al. 1996).

Related state of the world's birds case studies

• Seabird communities are declining in the Southern Californian Current System

References
del Hoyo, J.; Elliott, A.; Sargatal, J. 1996. Handbook of the Birds of the World, vol. 3: Hoatzin to Auks. Lynx Edicions, Barcelona, Spain.

Further web sources of information
Hear sounds for this species from xeno-canto, the community database of shared bird sounds from around the world.

View photos and videos, and hear sounds of this species from the Internet Bird Collection

Text account compilers
Butchart, S., Calvert, R., Ekstrom, J.

IUCN Red List evaluators
Butchart, S., Symes, A.

Recommended citation
BirdLife International (2013) Species factsheet: Ptychoramphus aleuticus. Downloaded from http://www.birdlife.org on 22/05/2013. Recommended citation for factsheets for more than one species: BirdLife International (2013) IUCN Red List for birds. Downloaded from http://www.birdlife.org on 22/05/2013.

This information is based upon, and updates, the information published in BirdLife International (2000) Threatened birds of the world. Barcelona and Cambridge, UK: Lynx Edicions and BirdLife International, BirdLife International (2004) Threatened birds of the world 2004 CD-ROM and BirdLife International (2008) Threatened birds of the world 2008 CD-ROM. These sources provide the information for species accounts for the birds on the IUCN Red List.

To provide new information to update this factsheet or to correct any errors, please email BirdLife

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