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Ptychoramphus aleuticus - Cassinís Auklet

Cassinís Auklet image

Geographic range:

Alaska to Baja California, Mexico

Key features:

A white spot above the eye is the best field mark for this small, chunky, almost all gray seabird. Its rapid flight is the best way to identify this non-descript bird, which has been described as looking like a flying tennis ball.


bay (rocky shore), bay (sandy shore), Continental shelf, continental slope, pelagic zone

Primary common name:

Cassinís Auklet

General grouping:

Seabirds and shorebirds

ITIS code:


Geographic Range

Range Description:

Cassinís Auklets inhabit the California Current Large Marine Ecosystem (CCLME), a region of the Pacific Ocean dominated by the southward traveling California Current and with multiple upwelling centers between British Columbia and southern Baja California, Mexico. Of the alcids, they are one of the most widely distributed in the Pacific. They breed on islands from middle Baja California to the Aleutian Islands, Alaska. Triangle Island, British Columbia has had an estimated 547,000 breeding pairs. Off the coast of San Francisco, the Farallon Islands have about 50,000 breeding pairs. The winter, non-breeding range of the Cassinís Auklet is poorly known. They appear in Monterey Bay after the breeding season from June to August. They are also found scattered off shore from October to January. They are most often found about 20 miles out, concentrating over upwelling regions near the rim of the Monterey Bay submarine canyon. During El Nino conditions they may be entirely absent. They will move to find food and may move south along the coast to winter in areas off Baja.

Subtidal depth notes:

Cassin's Auklet typically diver from 20-80 m in search of zooplankton prey.


bay (rocky shore), bay (sandy shore), Continental shelf, continental slope, pelagic zone


Relative abundance:

Common offshore of central California in fall and winter

Species Description

General description:

Cassinís Auklet is a small seabird with slate-gray to dull, gray-brown upper parts, pale gray underparts, and a white belly. It has small, white crescents above its pale yellowish white eye. Occasionally there will also be a smaller patch below the eye. There is no seasonal change in the plumage, although wear and tear will lead to a drabber looking bird. Its short and deep (about 2 cm by 1 cm) bill is pointed and black with a pinkish-white spot at the base of the lower mandible, visible only at close range. The bill of the female is not as deep as that of the male. The tail is short and the broad wings are rounded. The upper surfaces of its legs and three webbed toes are pearl blue. The undersides are black.

When assembled in breeding colonies they vocalize with an odd sound that has been described as frogs in full cry, or as squealing pigs, or as the creaking of an unoiled gate: kreek and ker-chuck. Most vocalizations occur at night on island breeding territories.

On land they half hop, half run, head held high, using their wings to help them scale rocks to a rocky perch. Cassinís Auklet has a rapid, direct flight with quick wing beats. They can fly from ground or sea surface without hesitation. Their flight has been described as looking like a flying tennis ball. They are best identified in flight, rather than by field marks seen when they are on the surface of the sea, as they almost disappear due to their plainness. They are excellent divers and fly underwater, using their feet as rudders. They are known to be able to dive to a depth of 43 m. After diving preening is common and bill dipping is observed and thought to be a method of rinsing off salt secretions.

Distinctive features:

Cassinís Auklet is small and chunky with a big plain gray head, short neck, bill, and tail, and a white spot above the eye. It is dark gray above and lighter gray below.


Length: 9 in Wingspan: 15 in Weight: 5.25 - 7 oz (northern birds heavier)

Natural History

General natural history:

Cassinís Auklet is a coastal, island-breeding, sociable seabird, preferring shallow burrows, which they dig with their sharp nails. Their nests may also be found in rock crevices, or under trees or logs. When not on the breeding grounds they spend most of their time at sea adjacent to their large breeding colonies, but often travel beyond the continental shelf for crustaceans, squid, and fish, where they will gather in large flocks if prey is abundant. They transport food back to their nests in a throat pouch (which is common to all five true auklets).

The timing of their breeding varies with latitude: in Baja California they nest in late fall whereas in Alaska they do not nest until early to mid-summer. In the southern range they are known to have two broods in a single breeding season where they may be found nesting every month of the year. This is unique to the Cassinís Auklet and not known in other alcids.

They spend their lives on the open ocean, except for their breeding season. If they are disturbed when on the surface they dive instantly. They spend daylight hours resting or feeding at sea and only come ashore after dark, where they find their mates and young with vocalizations. They will return to the sea before dawn unless they are incubating an egg or brooding a chick. They lay only one egg and the chick is brooded for 3 to 4 days until it can maintain its body temperature.

Cassinís Auklets have been divided into two subspecies: a northern form, P. a. aleuticus (from Alaska to Guadalupe Island, Mexico) and a southern form, P. a. australe (from San Benito Island, Baja California to Asuncion and San Roque Islands, Mexico). They are identical in appearance but australe is consistently smaller in length and mass.

In MBNMS the Cassinís Auklet is common offshore in fall and winter. Smaller numbers are present during spring and early summer. It rarely breeds in central California. The total estimated population is at least 3.57 million birds. Of the total, it is estimated that British Columbia has roughly 76%, Alaska 17%, California 4%, Washington 2.5%, Mexico 1%, and Oregon less than 0.01%.

Cassinís Auklet is named for John Cassin, a 19th century Pennsylvania businessman, ornithologist, and illustrator. A group of auks may be called a colony, loomery, or raft of auks.


Gulls, Ravens, Bald Eagles, Peregrine Falcons, Northwestern Crow, arctic fox, and river otters consume incubating adults, young and eggs. Foraging whales have been known to incidentally ingest Cassinís Auklets. In Alaska, introduced foxes have decreased breeding success in Cassinís Auklets.


Euphausiids (Thysanoessa spinifera and longipes), amphipods, copepods (often Neocalanus cristatus), squid, fishes (mainly Sebastes spp. and larval Citharichthys spp.) are the main prey items for the Cassin's Auklet. Initiation and extent of laying success are influenced by the occurrence of upwelling in the water near colonies and concurrent prey availability. Cold water is an indicator of strong upwelling and is highly correlated with breeding success.

Feeding behavior


Feeding behavior notes:

Cassinís Auklets dive for food, using their wings underwater for propulsion. They are often seen feeding in small groups and occasionally in large flocks. They will feed both day and night, staying down an average time of 42 seconds at depths from 20 to 80 m.

November - August


The onset of breeding behavior depends on their breeding location. In Baja Cassinís Auklets may lay eggs beginning in November and lasting 6 months. On the Farallon Islands early March to late April are typical months for reproduction, although courtship behavior has been seen as early as January, and second broods may occur as late as June or July. In British Columbia mid-April into late May is their season. On Triangle Island, off the coast of British Columbia, nearly one million Cassin's Auklets flock each year, making it the largest breeding colony of Cassin's in the world.

Courtship includes wing raising, bowing, head bobbing, bouncing, and a back step with cries of ďsqueerĒ and flying together toward the sea. They will also hop and run, chasing each other until one of the pair turns to face and bill with its mate. These behaviors are repeated throughout their season, especially when leaving or arriving at their burrow, and help maintain the pair bond. After copulation both birds rustle feathers, stretch their wings, and settle down face-to-face and begin more calling, billing, and head waggling. If one of the pair is lost, it will be replaced quickly.

Every type of island habitat is used for nesting: steep cliffs, level areas, sloped areas, covered with trees or treeless. Cavities are dug at night in the ground using their sharp toe nails and may take as long as three to four weeks to dig. The depth of the burrow is dependent on soil depth. They are generally about 3 feet deep. Rock crevices, piles of debris or driftwood, caves, under trees or cacti, grass or moss tussocks, or cracks in buildings will also suffice. Both members of the monogamous pair build the burrow adding very little, to no, nesting materials. The same burrow is used year after year.

Egg formation takes 12 to 13 days and is positively correlated to decreased sea surface temperatures. The female lays one 46 by 33.6 mm, unmarked, creamy-white egg; eggs in British Columbia are slightly larger and the yolk is flame scarlet. Both parents have two lateral incubation patches and immediately incubate it for about 5 Ĺ weeks, although 8 week incubations are also known. The pair alternates incubation duty every 24 hours. As the chick inside develops, the egg turns bluish or greenish. The chick begins pipping 24 to 72 hours before hatching. Upon hatching it is covered with soft black or gray down and needs parental care for the first 3 to 6 days for thermoregulation. In 11 days the egg tooth has worn off and feathers begin to appear at 12 to 16 days. After day 3 the chick is usually left in the burrow by day and fed by both parents at night. The chick nibbles at the white base of the lower mandible eliciting regurgitation of food from the throat pouch. The chick defecates near the cavity entrance and an active burrow with a chick may be recognized by pinkish deposits around the entrance. Juvenile plumage is visible by day 30.

Both parents care for the chick for 6 to 7 weeks. Chicks assume a low submissive posture when feeding and beg by constantly ďchirr-chirringĒ or ďsqueeringĒ until fed. Sipping sounds can then be heard between ďtwitteringĒ while feeding. Food is transported to the young from a throat pouch producing a milk-like mix, plus small marine invertebrates and larval fish. The chick is confined to its burrow until about day 30.

The chick may emerge to exercise its wings, stretch on tip toe with head and neck arched, and run short distances. By day 40 it tries short flights for up to 15 minutes, with clumsy landings. From day 41 to 50 it fledges, at any hour of darkness, and goes straight to the water and is able to swim and dive immediately and, it seems, is independent, apparently never associating with the parents after leaving. At this stage the eye is brown, but otherwise looks like a newly molted adult. It is believed that they do not breed until after their third year.

When conditions are favorable or if the first brood fails the pair may attempt a second brood.

August - October


The southern population of Cassinís Auklets appears to not migrate but stay in the vicinity of the breeding islands. The northern population (Alaska and British Columbia) moves southward and by fall from 500,000 to 1,000,000 birds have been counted off the California coast. The California breeders stay close to their breeding islands, primarily the Farallon Islands, and may return to their colony sites at night during any month. They may have a short-term dispersal to the Monterey Bay for feeding. Breeders from Oregon and Washington are believed to move southward, adding to the large numbers off California. Upwelling along the California coast makes it an ideal feeding ground, unless the jet stream is altered and upwelling is diminished.

Gulf of Farallones National Marine Sanctuary:

Oil spills are a real threat and result in heavy mortality from hypothermia and starvation. In 2005 a weather anomaly in the Gulf of Alaska apparently altered the jet stream, shifting it southward and delaying nutrient- rich upwelling. This led to 40,000 auklets on the Farallon Islands being unable to find adequate food, and abandoning their nests. This 2005 climate event highlights how the environment can alter the bottom of the food web and reverberate all the way up.

Monterey Bay National Marine Sanctuary:

Cassinís Auklets have suffered losses from introduced predators, primarily mammals. They are also easily disturbed by the presence of humans near their burrow when incubating and will desert their burrow. Walking on islands with burrows can cause burrows to collapse. The auklets will either re-excavate or abandon breeding for that year or re-lay another egg in a few days. Parents rarely desert hatched young.

Listing Status:

The IUCN lists them as of Least Concern.

Monitoring Trends:

An 11-year study at the Farallon Islands indicates that there has been a 49.7% decline in the Cassin's Auklet population at that site.
Click on an image below to view a larger version in the SIMoN Photo Library. You will also be able to view important information on each photo such as photographer, date, caption and more.
Ehrlich, P., D.S. Dobkin, and D. Wheye. 1988. The Birders Handbook: A Field Guide to the Natural History of North American Birds. Simon & Schuster Inc., New York. 785 p.
Lee, D.E., N. Nur and W.J. Sydeman. 2007. Climate and demography of the planktivorous Cassin's Auklet Ptychoramphus aleuticus off northern California: implications for population change. Journal of Animal Ecology, Volume 76, Issue 2:337-347.
NOAA. 1994. Beached marine birds and mammals of the North American West Coast: a revised guide to their identification. NOAA Sanctuaries and Reserves Division, U.S. Department of Commerce
Roberson, D. 2002. Monterey Birds 2nd edition. Monterey Peninsula Audubon Society, Carmel, CA. 536 p.
Sibley, D.A. 2000. The Sibley Guide to Bird. Alfred A. Knopf, Inc. 545 p.
Sydeman, W.J., R.W. Bradley, P. Warzybok, C.L. Abraham, J. Jahncke, K.D. Hyrenbach, V. Kousky, J.M. Hipfner, and M.D. Ohman. 2006. Planktivorous auklet Ptychoramphus aleuticus responses to ocean climate, 2005: Unusual atmospheric blocking? GEOPHYSICAL RESEARCH LETTERS, VOL. 33, L22S09.
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Audubon Society.
Accessed 02/28/09 for Marbled Godwit
Accessed 04/13/09 for Heermannís Gull
Accessed 03/15/2009 for Whimbrel
Accessed 06/20/2010 for Black Turnstone

Cornell Lab of Ornithology
All About Birds
Accessed 05/17/2009 for Albatross
Accessed 01/15/2009 for Clark's Grebe
Accessed 01/20/2009 for Great Egret
Accessed 02/03/2009 for American White Pelican
Accessed 01/30/2009 for Pelagic Cormorant
Accessed 02/12/2009 for Black-necked Stilt
Accessed 02/28/2009 for Marbled Godwit
Accessed 03/15/2009 for Whimbrel
Accessed 04/11/2009 for Long-billed Curlew
Accessed 04/13/2009 for Heermannís Gull
Accessed 09/10/2009 for Eared Grebe
Accessed 11/11/2009 for American Avocet
Accessed 01/26/2010 for Pigeon Guillemot
Accessed 12/15/2009 for Black-crowned Night Heron
Accessed 07/07/2009 for Pied-billed Grebe
Accessed 04/04/2010 for Osprey
Accessed 08/30/2010 for Ruddy Turnstone
Accessed 10/10/2010 for Pacific Loon
Accessed 10/15/2010 for Sooty Shearwater
Accessed 10/30/2010 for Surf Scoter
Accessed 12/04/2010 for Bufflehead
Accessed 02/01/2011 for American Coot
Accessed 02/20/2011 for Western Sandpiper
Accessed 03/04/2011 for Least Sandpiper.
Accessed for California Condor

Seattle Audubon Society.
Accessed 01/30/2009 for Pelagic Cormorant
Accessed 02/28/2009 for Marbled Godwit
Accessed 04/13/2009 for Heermannís Gull
Accessed 03/15/2009 for Whimbrel
Accessed 06/20/2010 for Black Turnstone
Accessed 12/15/2009 for Black-crowned Night Heron
Accessed 02/01/2011 for American Coot

WWW Field Guide to Birds of North America.
Accessed 12/30/2008 for Black-footed Albatross
Accessed 01/30/2009 for Pelagic Cormorant
Accessed 02/28/2009 for Marbled Godwit
Accessed 04/14/2009 for Willet
Accessed 04/13/2009 for Heermannís Gull
Accessed 09/10/2009 for Eared Grebe
Accessed 06/20/2010 for Black Turnstone
Accessed 12/15/2009 for Black-crowned Night Heron
Accessed 10/13/2009 for Horned Grebe
Accessed 10/10/2010 for Pacific Loon
Accessed 10/30/2010 for Surf Scoter
Accessed 02/01/2011 for American Coot
Accessed 02/20/2011 for Western Sandpiper
Accessed 03/04/2011 for Least Sandpiper.