Aethia pusillaleast auklet

Geographic Range

Least auklets (Aethia pusilla) are found in the northern Pacific. Populations are native to the United States, Russia, and Japan. Occasional vagrants are seen in Canada. ("BirdLife International", 2009; Jones, 1993)


The marine habitat of least auklets consists of near shore waters to deep, pelagic waters. Terrestrial habitat is occupied during the breeding season and consists of rocky coasts, talus slopes, and cliffs. ("BirdLife International", 2009; "NatureServe Explorer: An online encyclopedia of life", 2009)

Physical Description

Least auklets are the smallest of the auklets, weighing about 86 g and measuring about 16 cm in length. Basic plumage consists of black to brown on the back and a white, spotted, or black breast. Variation in chest color signals status. They have yellow eyes and black webbed feet. Males and females have colorful bills, horny knob ornaments, and white facial plumes during the mating season. (Jones, 1993; "NatureServe Explorer: An online encyclopedia of life", 2009)

  • Sexual Dimorphism
  • sexes alike
  • Average mass
    86 g
    3.03 oz
  • Average length
    16 cm
    6.30 in


Least auklets are monogamous colonial breeders. Colony size may reach as many as 100,000 breeding pairs or more. Nests are found on rocky coasts, offshore islands, coastal scree, and cracks in coastal cliffs. Nests are hidden under rocks and are often reused in following years. ("Alaska Seabird Information Series", 2006; "NatureServe Explorer: An online encyclopedia of life", 2009)

Least auklets lay only one egg at a time. Eggs are laid from June to August and take about 28 to 36 days for incubation. Young take about 26 to 31 days to fledge. It takes 3 or more years before least auklets breed for the first time. ("NatureServe Explorer: An online encyclopedia of life", 2009)

  • Breeding interval
    Least auklets breed once a year.
  • Breeding season
    Least auklets breed from June to August.
  • Average eggs per season
  • Range time to hatching
    28 to 36 days
  • Range fledging age
    26 to 31 days
  • Range time to independence
    26 to 31 days
  • Average age at sexual or reproductive maturity (female)
    3 years
  • Average age at sexual or reproductive maturity (male)
    3 years

Both parents take turns incubating the egg. After hatching, both continue to tend to the young. After fledging, there is no further parental care. ("NatureServe Explorer: An online encyclopedia of life", 2009)

  • Parental Investment
  • altricial
  • male parental care
  • female parental care
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • male
      • female
  • pre-weaning/fledging
    • provisioning
      • male
      • female
    • protecting
      • male
      • female


The average lifespan of least auklets is around 4.5 years. (Jones, 1993)

  • Average lifespan
    Status: wild
    4.5 years


Least auklets are relatively sedentary. During the non-breeding seaon, they move only as far as needed for food. They stay in the water except for breeding season when they move on shore. ("NatureServe Explorer: An online encyclopedia of life", 2009)

Communication and Perception

Least auklets communicate through vocalizations. They are very vocal when in breeding colonies. Adults have four kinds of vocalization: chatter, deep chatter, chirp, and chirr-buzz. They slowly rock their heads when alternating notes. ("NatureServe Explorer: An online encyclopedia of life", 2009)

Food Habits

Least auklets are invertivores. Adults dive into the water to find small crustaceans such as copepods and decapod larvae to feed upon. Young are fed by adults and mostly eat copepods so, during chick rearing, adults feed almost exclusively on copepods but may also eat krill. ("NatureServe Explorer: An online encyclopedia of life", 2009)

  • Primary Diet
  • carnivore
    • eats non-insect arthropods
  • Animal Foods
  • aquatic crustaceans


Arctic foxes (Vulpes lagopus) and Norwegian rats (Rattus norvegicus, a non-native species) are major predators to least auklets. Humans are also known predators. They hunt least auklets for food and occasionally least auklets are caught in fishing nets. ("NatureServe Explorer: An online encyclopedia of life", 2009)

  • Known Predators

Ecosystem Roles

There is little information on the ecosystem roles that least auklets play.

Economic Importance for Humans: Positive

Least auklets are sometimes used as food by indigenous populations.

  • Positive Impacts
  • food

Economic Importance for Humans: Negative

There are no known adverse effects of least auklets on humans.

Conservation Status

Although least auklet populations are declining due to predation and pollution such as oil spills, least auklets have a large range and population size so their current IUCN conservation status is Least Concern. ("IUCN Red List of Threatened Species", 2009)


Candace Rhodes (author), Florida State University, Emily DuVal (editor), Florida State University, Tanya Dewey (editor), University of Michigan-Ann Arbor.



living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

World Map


living in the northern part of the Old World. In otherwords, Europe and Asia and northern Africa.

World Map


uses sound to communicate


young are born in a relatively underdeveloped state; they are unable to feed or care for themselves or locomote independently for a period of time after birth/hatching. In birds, naked and helpless after hatching.

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.


an animal that mainly eats meat


uses smells or other chemicals to communicate


the nearshore aquatic habitats near a coast, or shoreline.


used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.


animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females


A substance that provides both nutrients and energy to a living thing.


offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

male parental care

parental care is carried out by males


makes seasonal movements between breeding and wintering grounds


Having one mate at a time.


having the capacity to move from one place to another.


specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.


reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.


An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).


the regions of the earth that surround the north and south poles, from the north pole to 60 degrees north and from the south pole to 60 degrees south.

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season


reproduction that includes combining the genetic contribution of two individuals, a male and a female


associates with others of its species; forms social groups.


uses touch to communicate


that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).


uses sight to communicate


2006. Alaska Seabird Information Series. U.S. Fish and Wildlife Services, 1: 75-76.

BirdLife International. 2009. "BirdLife International" (On-line). Accessed February 12, 2010 at

Cornell Lab of Ornithology. 1993. "Birds of North American Online" (On-line). Accessed February 12, 2010 at

IUCN. 2009. "IUCN Red List of Threatened Species" (On-line). Accessed February 12, 2010 at

NatureServe. 2009. "NatureServe Explorer: An online encyclopedia of life" (On-line). Accessed February 12, 2010 at

2009. Vocal Repertoires of Auklets: Structural Organization and Categorization. The Wilson Journal of Ornithology, 121(3): 568-584.

Jones, I. 1993. Least auklets (Aethia pusilla). Pp. 1-16 in A Poole, ed. Birds of North America Online, Vol. 69. Ithaca, New York: Cornell Laboratory of Ornithology. Accessed April 24, 2010 at