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Auks or alcids are of the family Alcidae in the order Charadriiformes. The alcid family includes the Uria, , Aethia, , and Brachyramphus. The family contains 25 extant or recently extinct species that are divided into 11 genera. Auks are found throughout the Northern Hemisphere.
Apart from the extinct great auk, all auks can fly, and are excellent swimmers and divers (appearing to "fly" in water), but their walking appears clumsy.
Extant auks range in size from the least auklet, at 85 g (3 oz) and , to the thick-billed murre, at and . Due to their short wings, auks have to flap their wings very quickly to fly.
Although not to the extent of penguins, auks have largely sacrificed flight, and also mobility on land, in exchange for swimming ability; their wings are a compromise between the best possible design for diving and the bare minimum needed for flying. This varies by subfamily, with the Uria guillemots (including the razorbill) and murrelets being the most efficient under the water, whereas the puffins and auklets are better adapted for flying and walking.
Auks are monogamous, and tend to form lifelong pairs. They typically lay a single egg, and they Philopatry year after year.
Some species, such as the Uria guillemots (murres), nest in large bird colony on cliff edges; others, such as the Cepphus guillemots, breed in small groups on rocky coasts; and the , auklets, and some murrelets nest in burrows. All species except the Brachyramphus murrelets are colonial.
The earliest unequivocal of auks are from the late Eocene, some 35 Mya. The genus Miocepphus (from the Miocene, 15 Mya) is the earliest known from good specimens. Two very fragmentary fossils are often assigned to the Alcidae, although this may not be correct: Hydrotherikornis (Late Eocene) and Petralca (Late Oligocene). Most extant genera are known to exist since the Late Miocene or Early Pliocene (about 5 Mya). Miocene fossils have been found in both California and Maryland, but the greater diversity of fossils and tribes in the Pacific leads most scientists to conclude they first evolved there, and in the Miocene Pacific, the first fossils of extant genus are found. Early movement between the Pacific and the Atlantic probably happened to the south (since no northern opening to the Atlantic existed), with later movements across the Arctic Ocean. The flightless subfamily Mancallinae, which was apparently restricted to the Pacific Coast of southern North America and became extinct in the Early Pleistocene, is sometimes included in the family Alcidae under some definitions. One species, Miomancalla howardae, is the largest charadriiform of all time.
The family contains 25 extant or recently extinct species that are divided into 11 genera. The extant auks (subfamily Alcinae) are broken up into two main groups - the usually high-billed puffins (tribe Fraterculini) and auklets (tribe Aethiini), as opposed to the more slender-billed murres and true auks (tribe Alcini), and the murrelets and guillemots (tribes Brachyramphini and Cepphini). The tribal arrangement was originally based on analyses of morphology and ecology. mtDNA cytochrome b sequences, and allozyme studies confirm these findings except that the Synthliboramphus murrelets should be split into a distinct tribe, as they appear more closely related to the Alcini; in any case, assumption of a closer relationship between the former and the true guillemots was only weakly supported by earlier studies.
Of the genera, only a few species are placed in each. This is probably a product of the rather small geographic range of the family (the most limited of any seabird family), and the periods of glacier advance and retreat that have kept the populations on the move in a narrow band of subarctic ocean.
Today, as in the past, the auks are restricted to cooler northern waters. Their ability to spread further south is restricted as their prey hunting method, pursuit diving, becomes less efficient in warmer waters. The speed at which small fish (which along with krill are the auk's principal prey) can swim doubles as the temperature increases from , with no corresponding increase in speed for the bird. The southernmost auks, in California and Mexico, can survive there because of cold . The current paucity of auks in the Atlantic (six species), compared to the Pacific (19–20 species) is considered to be because of extinctions to the Atlantic auks; the fossil record shows many more species were in the Atlantic during the Pliocene. Auks also tend to be restricted to continental-shelf waters and breed on few oceanic islands.
Hydotherikornis oregonus (Described by Miller in 1931), the oldest purported alcid from the Eocene of California, is actually a petrel (as reviewed by Chandler in 1990) and is reassigned to the tubenoses (Procellariiformes). A 2003 paper, "The Earliest North American Record of Auk (Aves: Alcidae) From the Late Eocene of Central Georgia", reports a Late Eocene, wing-propelled, diving auk from the Priabonain stage of the Late Eocene. These sediments have been dated through Chandronian NALMA {North American Land Mammal Age}, at an estimate of 34.5 to 35.5 million years on the Eocene time scale for fossil-bearing sediments of the Clinchfield Formation, Gordon, Wilkinson County, Georgia. Furthermore, the sediments containing this unabraded portion of a left humerus (43.7 mm long) are tropical or subtropical as evidenced by a wealth of warm-water shark teeth, palaeophied snake vertebrae, and turtles.
Biodiversity of auks seems to have been markedly higher during the Pliocene. See the genus accounts for prehistoric species.
Systematics
See also
Further reading
(1998). 9780198540328, Oxford University Press. ISBN 9780198540328
External links
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