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Cassin’s Auklet

Named after American ornithologist John Cassin, this seabird has a relatively small range and isn't too common.

A small, abundant alcid of the Pacific Coast, the Cassin’s Auklet migrates from its northern range but is sedentary farther south. Cassin’s Auklets are able to take flight from flat land or the water’s surface, with no need for an airborne jump or a running start. They propel themselves rapidly underwater using their wings.

Cassin’s Auklets nest in either natural crevices in rocks, or in burrows which they excavate with their sharp toenails, a process that can take several weeks. Young birds fledge while it is dark outside, most often just before dawn.


Description of the Cassin’s Auklet


The Cassin’s Auklet is a small, stocky, grayish seabird with pale eyes, a white spot above each eye, and a short, thick bill with a yellow spot at the base of the lower mandible.

Cassins Auklet

Photograph © Greg Lavaty


Sexes similar.

Seasonal change in appearance



Juveniles are similar to adults.


Oceans and islands.




Forages by diving underwater.


Breeds along the Aleutian Islands and western Canada south to Baja. Winters along most of the U.S. and Canadian west coasts.

Fun Facts

Researchers studying breeding Cassin’s Auklets must be careful not to collapse nest burrows when walking to visit nests.

Competition over perches sometimes leads to aggressive interactions.


Croaking is done on the breeding grounds.


Similar Species

  • Murrelets have extensive white on the throat and/or underparts and have dark eyes. Other auklets are darker above.


The nest is in a burrow or crevice.

Number: 1.
Color: White.

Incubation and fledging:
– Young hatch at 38-39 days.
– Young fledge (leave the nest) in 41-50 days after hatching.


Bent Life History of the Cassin’s Auklet

Published by the Smithsonian Institution between the 1920s and the 1950s, the Bent life history series of monographs provide an often colorful description of the birds of North America. Arthur Cleveland Bent was the lead author for the series. The Bent series is a great resource and often includes quotes from early American Ornithologists, including Audubon, Townsend, Wilson, Sutton and many others.

Bent Life History for the Cassin’s Auklet – the common name and sub-species reflect the nomenclature in use at the time the description was written.



Like the preceding species, the Cassin’s anklet is nocturnal in its habits on its breeding grounds, as it is distinctly a pelagic species and comes ashore only to breed, coming and going under the cover of darkness. Yet it is decidedly the best known of the anklets, as it has by far the widest breeding range, from the Aleutian Islands to central Lower California, and it is an abundant bird all along our Pacific coast at all seasons of the year.

Nesting: It is probably migratory to some extent, but, as with most of the Alcidae, its spring and fall migrations consist mainly of a movement onto its breeding resorts in the spring and departure from them to the open sea in the fall. Prof. Harold Heath (1915) says that “the natives state that Cassin anklet arrives on Forrester Island about March 1,” as it begins nesting early. In his account of the nesting habits of the species on this island he states that he was unable to distinguish any external mark of identification between the burrows of the Cassin’s auklet and the ancient murrelet.

It was accordingly impossible to determine the exact numbers of the two species. It can be said, however, that the Cassin auklet has been found to occupy several sites from the sea level to a height of 500 feet, and the presence of eggshell fragments in many places indicates their general distribution over the island and In small numbers on Lawrie and South Islands. As in the case of the ancient murrelet, the openings of the burrows are located about the roots of trees, or beneath partially burled logs or stones. The tunnel itself ranges from 2 to 4 feet in length, and is usually only sparingly branched. Whether they occupy the same home season after season is not known. It is certain, however, that several of the tunnels have been occupied at one time by mice, as Is evidenced by accumulations of gnawed cones in some of the lateral galleries or in the material scraped from the main canal and accumulated about the entrance.

On Forrester Island the duties of nest building are no more onerous than characterizes the species elsewhere. A few twigs of the Sitka spruce, together with old or mouse-eaten cones and occasional fragments of moss, appear to be all that is necessary. The length of the incubation period was not determined, though Captain John (a remarkably keen and accurate naturalist of the Haldah Tribe says that it lasts “about two weeks.” Fully three weeks more are required to bring the fledgling to the time of departure from the nest. During the time of Incubation the female occupied the burrow In five cases at least, and the Indians claim that she is fed during the night by the male and never leaves the nest until the young is several days old.

One of the most populous colonies of this species is to be found on the Farallone Islands, of which Mr. W. Leon Dawson (1911) writes:

The Cassin auklets are everywhere. Burrows predominate, but there is not a cleft, nook, crack, cranny, fissure, aperture, retreat, niche, cave, receptacle, or hidey-hole from the water’s edge to the summit of the light tower which is not likely to harbor this ubiquitous bird. The interstices of the stone wails contain them to the number of thousands. Every cavity not definitely occupied by puffin, petrel, or rabbit is tenanted by an auklet, and in many cases quarters are shared. if one’s imagination is not sufficiently stimulated by regular occurrences, It will be jogged by appearances in unexpected places: an old nest of rock wren or pigeon guillemot, an inner recess of a murre cave, an abandoned spur of puffin burrow, an overturned wheelbarrow or neglected board lying on the ground, driftwood on the beach: anything affording the slightest prospect of protection or cover. A pile of coal, sacked up and awaiting transfer from landing to siren, was found to be full of them. Since this was the rule from center to circumference of this magic isle, we conclude that the Cassin anklet is the commonest bird on the Farallones, and estimates of population anywhere short of one or two hundred thousand do not take account of the facts.

Mr. A. B Howell has sent me the followinig notes on the Cassin’s aukiet:

There are but few of the islands along the California coast and halfway down the peninsula of Lower California on which this anklet does not breed. Coming in from the sea it selects a suitable spot, usually more than 50 feet above the ocean, and tunnels out a burrow in the loam, which varies from one to several feet in lengtb. These are used year after year untii their entrances are big enough to fit a puffin. When available sites of this kind become crowded they readily occupy niches among the rocks and the corners of caves. The odor emanating from the burrows strongly reminds one of a badly kept chicken house. Fresh eggs are found by the middle of March and may be found in numbers until the middle of July. though the nesting season would seem to vary greatly in dIfferent years. Of perhaps 50 nests examined by me on Los Coronados Islands the first part of July, 1910, all held eggs in various stages, except three which contained small young. On June 30, 1913, this order was reversed, and out of many nests examined by Messrs Dickey, van Rossem, and myself three eggs were obtained, and the remainder held young in all stages. It is also worthy of note that at the latter time there were not nearly as many birds breeding as at the former. The eggs are deposited on the bare ground or occasionally a few bits of weed.

Mr. Chase Littlejohn sent the following notes to Major Bendire:

This anklet arrives at the island, on which It Intends to nest, between 9.30 and 10 in the evening, according as the weather is clear or cloudy: the darker the sky the earlier they come: and immediately drop into the grass and are soon in their holes, where they both take a hand in digging and cleaning out whatever has accumulated since it was last occupied. After this house cleaning is done, or a new hole is dug, the nest is made, the egg deposited, and Incubation begins at once, which is taken part in by both parents, and as near as I could determine these duties are exchanged nightly; while one sets the other is away, far at sea, on the feeding grounds. On his or her return to the hole s greeting note Is sounded, and immediately the one on the nest answers and comes to within a few inches of the entrance to meet the mate which has just returned. Here the peculiar rasping love note is repeated over and over with hardly an intermission for at least half an hour (I have listened that long), sometimes by one and oftener by both. While this salutation is going on they sre constantly bowing to each other, and so absorbed are they in their greeting that the hand can often be placed on them for a short time without attracting their notice, probably each thinking it is the other that is doing this, but when the discovery is made that there is an intruder about they at once scurry into the farthest end of their hole, which is from 2 to 6 feet long, and there remain quiet. At the end of the hole the nest Is situated and is composed of a few coarse grass blades, or oftener of the large flower stems of a plant known to the natives as pooch-ki, and which is eaten by them: the natives: the same as we use celery. These stalks are from one-half to 1 inch in diameter and often 18 Inches long; they are cut into lengths by the birds using their beaks for that purpose. One remarkable thing about these holes is no matter how close they may be to each other no two ever intersect, although they wind in and out, up and clown in every (lirection. Another peculiar and interesting habit is that each hole is supplied with a short side tunnel a foot or so in length, in which the birds deposit their excrement. The nest is always very clean. The love or greeting note mentioned above can be produced, as near as I could get it, by the syllables kwee-kaw repeated over and over. In listening to it one could not help thinking of the sound made by a squeaky bucksaw in a splintered log of wood. They also utter a peculiar gnawing, grunting sound which I was unable to put on paper. They are very pugnacious when taken In the hand and will scratch and bite very hard, often drawing blood. For food they are, strange to say, excellent, being the only sea bird with which I am acquainted that Is even passable.

Eggs: The single unmarked egg of Gassin’s auklet is between “ovate” and “elliptical ovate” in shape, usually nearer the former and with nearly equally rounded ends, but some eggs are quite pointed at one or even both ends. The shell is smooth, but quite lusterless. The color is dull white, milk white, or creamy white, but the egg shows a decidedly bluish or greenish tinge when held up toward the light. The egg is usually somewhat, and often much, nest stained. The measurements of 60 eggs, in the collection, average 46.9 by 34.3 millimeters; the eggs showing the four extremes measuring 51 by .34.5, 45 by 37, 44 by 34, and 45 by 31.5 millimeters.

Both sexes incubate, relieving each other during the night. The universal rule among sea birds is to raise only one brood during the season, but there is considerable evidence to show that this species is an exception to the rule. The breeding season is much prolonged, from April to November, which means that more than one brood is raised or that the breeding grounds are so overcrowded that different individuals have to breed at different seasons. The former supposition seems to be the more likely. Mr. Walter E. Bryant (1888) says:

Several young are supposed to be raised during the season. Many nests were found occupied by young In down and one adult bird sitting upon a fresh egg; in some nests the egg was kept warm by contact with the young. In no Instance were two old birds found in the same nest, and no birds were found at the time search was made without an egg or young, or both. The majority of the adult birds were females, although both sexes were found sitting. If provoked, either young or old will seize a finger and hold on. The old birds are silent when on the nest, but the downy young make a faint peeping when disturbed. When taken from the nest they endeavor to crawl out of sight, and if tossed into the air they descend quickly and hide themselves from the light. They commenced flying this year as early as April 2, and eggs have been found as late as November 20, showing a breeding time extending through eight months.

Mr. A. W. Anthony, in his notes sent to Major Bendire, refers to a nest “containing a nearly fledged young and an adult female lncubating a fresh egg; the fledgling was crowded into a branch burrow away from the main nest.” Mr. W. Otto Emerson, in his notes, states that two or three broods are raised and that he has found fully grown young in the same hole with the parent bird sitting on the second laying. Possibly in all of these eases the young bird and the egg may have belonged to different parents, but this hardly seems likely, unless the young bird may have been sufficiently frightened by the process of opening the burrow to have run into a compartment occupied by an incubating bird. If this bird is such o prolific breeder as it seems to be this would account for its great abundance over such a wide breeding range.

Young: Mr. Emerson gives the period of incubation as 21 days and Mr. Littlejohn as 30 days. The chick remains in the nest and is fed by its parents on regurgitated food until it is fully fledged and able to fly. Mr. Emerson says that the young are fed in the same manner that a pigeon feeds its young, the parent throwing up a thick, creamy, chocolate-colored matter, containing what he took to be small marine insects. He says that the young become “rolling fat while in their holes and the old birds are never poor from the cares of incubation.” The young remain in the burrows until able to fly.

Plumages: The downy young is “Blackish brown” or “fuscous black” when first hatched, fading to “fuscous” or “hair brown” when older, on the upper parts; the throat, breast, and flanks are paler; and the belly is “ecru drab,” “drab gray,” or “drab.” According to Mr. Howell’s observations, “pin feathers begin to show at the base of the down when the chick is but 2 or 3 days old. They first show through on the underparts, then on the head, and the down gradually is shed from the end of the feathers until a small tuft below the chin is all that remains.” The first plumage, which is thus acquired directly from the downy stage, is not strikingly different from that of the adult. The bill is decidedly smaller, however, the throat is whiter and the wings and tails are browner in young birds. The first nuptial plumage shows no very marked change and the young bird closely resembles the adult; birds with smaller bills and slightly whitish throats are probably young birds. Adults have no conspicuous seasonal changes of plumage, except that the fall plumage looks brighter and fresher. The clear, slatyblue and black plumage of adults in the fall, together with the larger bills, will usually serve to distinguish them from young birds.

There is apparently a complete molt in August and September and probably a partial prenuptial molt during the latter part of winter.

Food: Cassin’s auklets feed well out at sea, where they spend most of their time, singly, in pairs, or in small flocks; some of their food is obtained on or near the surface, but they must dive to con siderable depths for some of it. Mr. F. Stephens (1893) found that: The stomachs of some examined contained shrimps. For some it simply dipped its head under water, for others it clove a few inches.

Mr. Emerson noted marine insects among its food and Professor Heath (1915) says:

The food of the young, and of the aduits as well, was found to consist of copepods and an undetermined species of shrimp or amphipod.

Probably a great variety of small marine animals are included in its diet.

Behavior: T he flight of Cassin’s auklet is swift, steady, and direct; when flying over the water it flies low, just clearing the waves, and even over the land its flight is low. Mr. Bryant (1888) writes that: One, attracted by a lantern carried by Mr. Emerson, flew with characteristic swiftness directly at it, but missed and struck against the side of a house, ~~-here it was picked up stunned. Auks have struck persons walking without a light, hut always belo~v the shoulders.

Referring to the clumsiness of this species, Mr. Dawson (1911) writes:

The Cassin aukiet seems incapable of controiling the force of its flight, and the wonder is that the birds are not every one of them dashed to pieces in a single night. In this respect they remind one of nothing else so much as beetles or moths, which come hurtling into the region of candlelight, crash against the candlestick, and without an instant’s pause begin an animated search afoot. This crash-and-crawl method seems not exceptional but characteristic in the aukiet. It was especially noticeable in the paved area just outside our workroom door. Crash! announced the arrival of another food-laden messenger from tie unkno~vii deeps. The impact of collision with the building invariably stunned the bird so that it fell to the ground, but it Immediately began a frnntic ~enrcli, and as likely as not, before you could lay hands on It, disappeared in a clack under the doorstep.

Mr. Stephens (1893) says:

They ,iive well, and can stay under water two minutes or more. They swim fast for so small a bird. On being chased with a boat they often preferred diving to flight, and then their speed was greater than when swimming, requiring sharp rowin~ to get within shooting distance. They often changed their course while under water, and several times baffled me in that way. They are so small that one can not see them very far in rough water. Wounded birds observed at short distances were observed to use their wings in diving, and probably In nil cases diving is simply a flight under water.

Although apparently a silent bird at other times, this aukiet is a very noisy bird on its breeding grounds at night.. Mr. Dawson’s (1909) graphic pen describes the evening concert as follows: The stage setting is perfect, down to the footlights. Now, for the orchestra: “Petteretteretterell, etteretterettereJi “: it is the tap, tap of the petrel conductor calling the island to attention. Soon ghostly forms steal about in the gathering gloom. Voice answers voice as each moment flies. The flitting shadows become a throng and the chorus a tumult. But in the grand melange there is a new note. A quaint burring croak wells up from the ground, elfish, gruesome, portentous. The Cassin auklets are waking up. Heard alone, the auklet chorus reminds one of a frog pond in full cry. As one gives attention to an individual performer, however, and seeks to locate him in his burrow, thc mystery and strangeness of it grows. The vocalist is complaining bitterly of we know not what wrongs. We must be within 3 feet of the noise as we stoop at the burrow’s mouth; the volume of it is earfilling; yet its source seems furlongs off. Now it is like the squealing of a pig in a distant slaughter pen. We lift our heads, and the stockyards are reeling with the prayers and cries of a thousand victims. And now the complaint falls into a cadence, “Let meee out, let meee out, let me out.” A thousand dolorous voices take up the chorus. The uproar gets upon the nerves. Is this a bird lunatic asylum? Have we stumbled upon an avian madhouse here in the lone Pacific? And are these inmates appealing to the moon, their absent mistress?

Mr. Charles A. Keeler (1892) says:

Their note resembles the creaking of a rusty gate, and may be represented by the syllables creek a reek, creek a reek, creek a reek.

Cassin’s auklets, especially when fat, make very good eating, and have doubtless been used largely for food by many tribes of Indians or by fishermen. Professor Heath (1915) says:

In ancient times this species figured largely in the natives’ bill of fare, and large numbers were annually taken by means of snares or were attracted by bonfires and subsequently knocked down.

Large numbers of Cassin’s auklets are occasionally washed up dead on the beaches of our Pacific coast. Mr. J. H. Bowles (1908)

discovered that, in one case at least, this mortality was due to an epidemic of intestinal tapeworms. In addition to finding dead birds of this and other species strewn along the beach, he noted that: The ocean was rather plentifully dotted with sick birds, some of them so close in as to be rolled over and over in the breakers.

The intestines of a shearwater were packed solid with tapeworms.

These worms were about 3 inches long, rather slender, and marked with alternate rings of white and brownish black. There were many hundredq of the disgusting parasites in every bird, making death from starvation an absolute certainty.

Mr. Howell writes me that on the Coronados Islands: These birds suffer a great dsal from the depredations of duck hawks, a pair or two of which are usually found near the auklet colonies. Even though the latter attain an amazing speed when pitching from the top of the Islands when released from the hand, the falcons overtake them with the greatest ease and continue to slaughter, after their hunger has been appeased, for the mere fun of it. This is perhaps xvhy the aukiets visit the colonies only after nightfalL

Winter: The fall migration is not well marked, and probably the winter home of this aukiet is ot far from its breeding grounds, as it apparently spends the winter at sea throughout most of its summer range.

Breeding range: Pacific coast, from Lower California (Cerros, San Benito, San Geronimo, San Martin, Todos Santos, and Los Coronados Islands) northward to southern Alaska (Forrester Island, Egg Island, 200 miles west of Fort Wrangell and Sanak Islands) and the Aleutian Islands (Atkha Island). North of California it is somewhat local in its distribution.

Winter range: The open sea in the vicinity of its breeding places at least as far north as Washington (Puget Sound).

Casual records: It is said that a specimen taken in Kamtschatka is in the Berlin Muse~’m.

Egg dates: Farailone Islands: 64 records, April 3 to July 20; 32 records, May 29 to June 18. Lower California: 29 records, March 10 to June 8; 15 records, April 6 to May 18. Santa Barbara Islands: 10 records, May 16 to June 29; 5 records, June 4 to 9. Sanak Islands, Alaska: 2 records, June 6; 2 records, June 7; and 1 record, July 3.

About the Author

Sam Crowe

Sam is the founder of He has been birding for over 30 years and has a world list of over 2000 species. He has served as treasurer of the Texas Ornithological Society, Sanctuary Chair of Dallas Audubon, Editor of the Cornell Lab of Ornithology's "All About Birds" web site and as a contributing editor for Birding Business magazine. Many of his photographs and videos can be found on the site.

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