Cassin's auklet - Ptychoramphus aleuticus

Taxonomy & Nomenclature

Scientific Name Ptychoramphus aleuticus
Author (Pallas, 1811)
Taxonomic Rank Species
Taxonomic # 177013
Common Names English: Cassin's Auklet
Spanish: Alcuela oscura
French: Starique de Cassin
Spanish: Mérgulo sombrío
Portuguese: mérgulo-sombrio
Current Standing valid
Taxonomic Parents Kingdom: Animalia
  Phylum: Chordata
    Subphylum: Vertebrata
      Class: Aves
        Order: Charadriiformes
          Family: Alcidae
            Genus: Ptychoramphus
Taxonomic Children Subspecies: Ptychoramphus aleuticus aleuticus
Subspecies: Ptychoramphus aleuticus australis
Synonyms (since 1950)

Taxonomic data is courtesy of the Integrated Taxonomic Information System (ITIS)
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Physical Description / Field Identification

Ptychoramphus aleuticus is a small alcid, weighing approximately 175 grams. They have a short dark bill with a yellow base, a white belly, blue feet, and white undertail coverts. Cassin’s auklets have dark gray underparts, with a gray chin, throat, flanks and breast. They have a broken white ring surrounding their eye.

Adult females have a shallower bill, but are otherwise similar to adult males in size and coloration. Juvenile P. aleuticus are slightly paler than adults and have white throats. The color of the eye can supposedly be used to age auklets. The subspecies P. a. australis is smaller in length and mass.

The simplest way to identify a Cassin’s auklet in the field is by their lack of head ornamentation (common with other alcids). If they are seen from afar, their rapid wingbeat and broad wings may be helpful in identification. If seen from a short distance, the broken white eye ring (like a white eyebrow) is useful for identification.

Can be Confused With

The mostly gray neck and breast make the Cassin’s auklet identifiable from other similarly sized murrelets. The rhinoceros auklet (Cerorhinca monocerata) is considerably larger, and has a yellowish bill.


The Cassin’s auklet breeds on offshore islands from Baja California to the Aleutians in Alaska. Subarctic species with a large marine range restricted to the eastern North Pacific and the Bering Sea. Southern extent of the marine distribution related to cool waters of the California Current and areas influenced by coastal upwelling, particularly off Baja California. Range extends north along the west coast of North America into the Bering Sea in summer and fall.

The two subspecies have different distributions: the Northern P. a. aleuticus is found from the Sanak Islands, Alaska to the Channel Islands in southern California. The northern populations engage in seasonal migrations. The southern P. a. australis breeds off the Baja Peninsula of California and Mexico. The southern populations do not appear to migrate seasonally.

Ecology and Behavior

Cassin’s auklets inhabit the continental shelf and slope.  They are known to aggregate at the shelf-break (200 m isobath) to forage on euphausiids, particularly offshore of breeding colonies in central California.  However, foraging distributions during the breeding season may be also influenced by the extent of frontal systems and upwelling plumes.

Cassin’s auklets come to land exclusively to breed. They are generally silent while at sea, but adults at breeding colonies call during the night.

Feeding and Prey

Cassin’s auklets pursue prey underwater, using their wings for propulsion. They forage nocturnally to avoid predation from large gulls at the breeding colonies.

Diet consists almost exclusively of Crustaceans (Euphausids and copepods), though larval fish and squid are occasionally taken (crustaceans > fish > squid).

Pey species include:

• Crustaceans: Acanthomysis columbiae, Euphausia pacifica, Neocalanus cristatus, Nyctiphanes simplex, Phromena sp., Thysanoessa spinifera, Thysanoessa longipes

• Fish: Citharichthys sordidus, Sebastes sp., Hemilepidotus sp., Pleuronectes sp.

• Cephalopods: Unidentified squid

Threats and Status

Main threats include:

• Predators at colonies

• Oil and plastic pollution

• Fisheries bycatch



Gaston, A.J., I.L. Jones and I. Lewington. 1998. The Auks: Alcidae. Bird Families of the World, Vol. 5. Oxford University Press, Oxford.

Hunt, G.L., Jr., H. Kato and S.M. McKinnell, eds. 2000. Predation by marine birds and mammals in the subarctic North Pacific Ocean. PICES Scientific Report No. 14. North Pacific Marine Science Organization, Sidney.

Vermeer, K., K.H. Briggs and D. Siegel-Causey, eds. 1993. The status, ecology, and conservation of marine birds of the North Pacific. Special Publications Canadian Wildlife Service, Ottawa.

Manuwal, D.A. and A.C. Thoresen, A.C. 1993. Cassin's Auklet (Ptychoramphus aleuticus). pp. 1-18 in A. Poole and F. Gill, eds. The Birds of North America, No. 50. The American Ornithologists’ Union, Washington, DC.

ITIS TSN177013
Status - ESA, U.S. FWS
Status - Red List, IUCN
    NT (Global)
#records (spatial)14,139
#records (non-spatial)0
Year1970 - 2017
Latitude29.86 - 71.04
Longitude-159.81 - 226.91
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