E-Fauna BC: Electronic Atlas of the Wildlife of British Columbia

Aethia pusilla (Pallas)
Least Auklet
Family: Alcidae

Species account author: Jamie Fenneman

© Martin Meyers  Email the photographer   (Photo ID #12768)


Distribution of Aethia pusilla in British Columbia.
(Click on the map to view a larger version.)
Source: Distribution map provided by Jamie Fenneman for E-Fauna BC

Species Information

Breeding adult
This plumage is acquired in early spring (~April) and is retained until fall (~September). The upperparts (including the upperwings and short tail) are entirely blackish with the exception of a pair of variable white patches across the scapulars (largely lacking on some individuals) and narrow white tips to the secondaries that form a narrow white trailing edge to the wing. The underparts are whitish with variable blackish spotting and mottling that is generally densest and heaviest on the breast. Some individuals have almost pure white underparts, while others show so much dark mottling that it almost obscures the white background colour; most individuals are between these extremes. The greater underwing coverts are paler and greyish, showing as a pale underwing bar in flight. The head is blackish, with fine white speckling on the forehead, a variable short white plume behind the eye, and a sharply defined white throat patch. The iris is whitish, the tiny, stubby bill is dull reddish with a blackish base and a tiny dark knob at the base of the upper mandible, and the legs and feet are blackish-grey.

Non-breeding adult
This plumage is held between ~September and ~April. It is overall similar to the breeding plumage, but the entire underparts, breast, foreneck, and throat are white (no dark mottling), with the white curling around the rear edge of the ear coverts and often approaching or joining the reduced white eye plume. Bare part colouration is similar to the breeding adult, although the small knob on the bill is shed during the mid- to late summer and is not retained through the winter.

Juvenile
This plumage is held from late summer through the first winter, being lost in late winter or early spring (March-April). It is similar to the non-breeding adult, but the underparts may show some fine grey scalloping or scaling, the white plume behind the eye is entirely lacking, the bill is dark, and the iris is grey.

Measurements
Total Length: 15.5-16 cm
Mass: 70-101 g

Source: Jones (1993); Sibley (2000)

Biology

Identification

This is a truly tiny seabird, scarcely larger than a sparrow, and its small size alone is highly diagnostic. It is most likely to be confused with other small alcids such as Cassin’s Auklet and, potentially, Ancient Murrelet or non-breeding Marbled Murrelet. Although similarly black and white, the murrelets are noticeably larger than the Least Auklet with a very different structure. At close range, note the pale eyue of Least Auklet (dark in both of the murrelets), its tiny and stubby bill, and its chunky proportions. Cassin’s Auklet is slightly more similar in size and structure, although it is still noticeably larger than Least Auklet. Adult Cassin’s Auklet has a pale eye, similar to the Least Auklet, but is almost entirely grey, unlike the contrasting black and white plumage of the Least Auklet. This feature alone should be enough to distinguish the two species under virtually any circumstances.
Vocalizations

Although this species is highly vocal around its breeding colonies, it is essentially silent at sea.

Source: Sibley (2000)

Breeding Ecology

The Least Auklet is a vagrant to British Columbia and does not breed in the province.
Foraging Ecology

This species feeds exclusively on marine zooplankton, showing a particular affinity for tiny calanoid copepods. More so than other auklets, the at-sea distribution of the Least Auklet is closely tied to marine areas with considerable upwellings and thermoclines that result from prominent underwater hydrography (canyons, seamounts, etc.). All food items are secured during relatively shallow dives (generally 15-25 m), during which the auklet propels itself solely using its wings. It is characteristically extremely agile during these high velocity dives.

Source: Jones (1993)

Habitat


This species is strictly marine throughout its range, including the single vagrant in B.C. The B.C. individual frequented nearshore marine waters off a rocky coastal headland, presumably due to the known upwellings that occur at the site (and that attract massive numbers of various species of seabird). This species could also inhabit (and may be more likely to inhabit) deep offshore waters, including those beyond the continental slope, and is not strictly confined to nearshore environments.

Source: Jones (1993)

Distribution

Global Range

Breeds primarily on the islands of the Bering Sea and Aleutian archipelago in western Alaska, as well as along the southern coast of the Alaska Peninsula in south-coastal Alaska. Additional populations also breed on islands off eastern Siberia. Wintering birds occur largely in waters of the southern Bering Strait and throughout the Aleutian Islands, as well as off the coast of eastern Siberia and northern Japan. This species is exceedingly rare as a vagrant outside of its normal range, with isolated records of single birds from the Northwest Territories, California, and British Columbia.
BC Distribution

Vagrancy
Accidental in extreme southwestern B.C. It is kown in the province only from a (presumably) single individual that returned to the same location on southern Vancouver Island for three consecutive years between 2007 and 2009. The appearance of this bird was primarily during August and September, although in 2009 it was observed several times during June, suggesting that it may have spent the entire summer period in the vicinity.

The dates of observations of this individual, all of which are from the Shirley area near Sooke, are as follows:

2007: September 2
2008: August 31 & September 6
2009: June 19 & 27; August 8

Conservation

Population and Conservation Status

This North Pacific seabird is often exceptionally abundant in the areas where it breeds, with some colonies exceeding 1.5 million individuals. The total North American breeding population has been estimated at 9,000,000 individuals, which is particularly impressive given its restricted breeding distribution. Curiously, however, this species is unusually scarce as a vagrant outside of western Alaska, with only three confirmed occurrences. This may be due to its largely pelagic lifestyle combined with its diminutive size. Nonetheless, this species remains abundant and secure in Alaskan waters and additional vagrant records could be expected to occur, particularly south along the Pacific coast.

Source: Jones (1993)

Taxonomy


This species is monotypic, with no recognized subspecies.

Status Information

Origin StatusProvincial StatusBC List
(Red Blue List)
COSEWIC
UnlistedUnlistedUnlistedUnlisted
BC Ministry of Environment: BC Species and Ecosystems Explorer--the authoritative source for conservation information in British Columbia.

Additional Range and Status Information Links

Additional Photo Sources

General References


Recommended citation: Author, Date. Page title. In Klinkenberg, Brian. (Editor) 2019. E-Fauna BC: Electronic Atlas of the Fauna of British Columbia [efauna.bc.ca]. Lab for Advanced Spatial Analysis, Department of Geography, University of British Columbia, Vancouver. [Accessed: 21/11/2019 7:15:54 PM]
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