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Cassin's Auklet Life History


OceansCassin’s Auklets spend most of their lives on the open ocean, far from land. They forage where food is concentrated by ocean currents, including upwellings, over the continental shelf and slope. They nest on oceanic islands from Alaska to Mexico. They use almost any island habitat, whether mountainous or flat, forested or barren, provided it has adequate rocky crevices for nest sites, or stable soil for excavating burrows. However, they avoid densely forested areas and terrain with tall, thorny vegetation. Back to top


Aquatic invertebrates

Cassin’s Auklets eat small fish, squid, and crustaceans, which they capture by diving below the sea surface, “flying” underwater with their short, broad wings, and seizing prey in the bill. Most dives are less than 50 feet, but they are capable of diving over 100 feet deep. Prey include Pacific whiting, Pacific herring, northern anchovy, lingcod, and various species of rockfish (genus Sebastes), sculpin (Hemilepidotus), and flatfish (Pleuronectyes and Citharicthys). They also eat fish eggs, Dungeness crab larvae, larval squid, and a great variety of tiny crustaceans known as copepods, euphausiids, amphipods.

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Nest Placement

BurrowMale and female Cassin’s Auklets select a nest site together, either in a rocky crevice or in soil, and make a burrow with their feet. They lay eggs at the end of the burrow or at the back of the crevice. In Mexico, some birds nest on top of the ground, underneath cacti. Cassin’s Auklets also readily accept artificial nest boxes.

Nest Description

Rock crevices used for nesting are sometimes very shallow (just 4 inches deep), but burrows made in soil are usually at least 3 feet deep. These burrows are about 5.5 inches in diameter, and the nest area, which is not lined, measures about 6.7 inches wide by 4.7 inches tall in burrow nests. Some nests situated under cacti are simple scrapes.

Nesting Facts

Egg Description:Creamy white.
Condition at Hatching:Hatchlings have a full coat of gray down.
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Surface Dive

Cassin’s Auklets return to most breeding areas in spring, with some exceptions. In Mexico and part of California, they breed in late autumn or winter, and in the southernmost part of their range, they may continue breeding for much of the following year. Pairs perform courtship displays under cover of darkness (for protection from predators, such as gulls). Male and female greet one another by stepping backward and bowing. In other displays, they circle each other, step to the side, bob and wag their heads, look away, and raise one wing, all while giving twittering, screeching calls. Pairs also perform billing, in which they touch and tremble their bills together, and allopreening, in which they nibble the feathers on each other’s necks and faces. Just before dawn and after dusk, nesting colonies resound with their high-pitched, grating calls, each claiming territory from its burrow. Cassin’s Auklets are socially monogamous, with males sometimes mating with a second female. Males approaching another pair’s burrow might be driven off with threats, pecks, or even physical clashes, in which both birds raise their wings, tails, and head feathers, wag the head side-to-side, and then fight like domestic chickens with leaping attacks. Sometimes, early in the breeding cycle, multiple birds engage in chasing and fighting. Birds studied year-round in California appear to be territorial and defend their burrows year-round, but do not vocalize from the burrow during the nonbreeding season. In Mexico, when food resources permit, Cassin’s Auklets often have two nesting seasons—unique among the world’s alcids. When not at breeding colonies, they forage at sea, usually alone or in pairs. Where food is plentiful, sometimes flocks of thousands gather and give twittering calls, especially when conditions are foggy.

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Low Concern

Partners in Flight estimates a global breeding population of 3.6 million and rates the species a 14 out of 20 on the Continental Concern Score. They include Cassin’s Auklet on the Yellow Watch List for species showing a rapid decline in population over the last 40 years. Colonies are threatened by introduced predators (cats, foxes, and rats), and grazing animals (goats and cattle) that trample burrows or nests. Many auklets drown in fishing nets. The species is also vulnerable to oil spills, pesticides, and plastic pollutants, and to the effects of climate change, particularly where changes in ocean currents affect prey resources.

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Ainley, D. G., D. A. Manuwal, J. Adams, and A. C. Thoresen (2011). Cassin's Auklet (Ptychoramphus aleuticus), version 2.0. In The Birds of North America (P. G. Rodewald, Editor). Cornell Lab of Ornithology, Ithaca, New York, USA.

Kushlan, J. A., M. J. Steinkamp, K. C. Parsons, J. Capp, M. A. Cruz, M. Coulter, I. Davidson, L. Dickson, N. Edelson, R. Elliott, R. M. Erwin, S. Hatch, S. Kress, R. Milko, S. Miller, K. Mills, R. Paul, R. Phillips, J. E. Saliva, W. Sydeman, J. Trapp, J. Wheeler and K. Wohl (2002). Waterbird conservation for the Americas: The North American waterbird conservation plan, version 1. Washington, DC, USA.

Lutmerding, J. A. and A. S. Love. (2020). Longevity records of North American birds. Version 2020. Patuxent Wildlife Research Center, Bird Banding Laboratory 2020.

Lutmerding, J. A. and A. S. Love. Longevity records of North American birds. Version 2021.1. Patuxent Wildlife Research Center, Bird Banding Laboratory 2021.

Partners in Flight. (2020). Avian Conservation Assessment Database, version 2020.

Sibley, D. A. (2014). The Sibley Guide to Birds, second edition. Alfred A. Knopf, New York, NY, USA.

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