Auk


An auk or alcid is a bird of the family Alcidae in the order Charadriiformes. The alcid family includes the murres, guillemots, auklets, puffins, and murrelets. The word auk is derived from Icelandic álka, from Old Norse alka, from Proto-Germanic *alkǭ.
Apart from the extinct great auk, all auks are notable for their ability to "fly" under water as well as in the air. Although they are excellent swimmers and divers, their walking appears clumsy.
Several species have different common names in Europe and North America. The guillemots of Europe are referred to as murres in North America, if they occur in both continents, and the little auk is referred to as the dovekie.

Description

Auks are superficially similar to penguins having black-and-white colours, upright posture and some of their habits. Nevertheless, they are not closely related to penguins, but rather are believed to be an example of moderate convergent evolution. Auks are monomorphic.
Extant auks range in size from the least auklet, at 85 g and, to the thick-billed murre, at and.
Due to their short wings, auks have to flap their wings very quickly in order 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, the Uria guillemots and murrelets being the most efficient under the water, whereas the puffins and auklets are better adapted for flying and walking.

Feeding and ecology

The feeding behaviour of auks is often compared to that of penguins; both groups are wing-propelled pursuit divers. In the region where auks live, their only seabird competition are cormorants. In areas where the two groups feed on the same prey, the auks tend to feed further offshore. Strong-swimming murres hunt faster schooling fish, whereas auklets take slower-moving krill. Time depth recorders on auks have shown that they can dive as deep as 100 m in the case of Uria guillemots, 40 m for the Cepphus guillemots and 30 m for the auklets.

Breeding and colonies

Auks are pelagic birds, spending the majority of their adult life on the open sea and going ashore only for breeding, although some species — like the common guillemot — spend a great part of the year defending their nesting spot from others.
Auks are monogamous, and tend to form lifelong pairs. They typically lay a single egg, and they are philopatric.
Some species, such as the Uria guillemots, nest in large colonies on cliff edges; others, like the Cepphus guillemots, breed in small groups on rocky coasts; and the puffins, auklets, and some murrelets nest in burrows. All species except the Brachyramphus murrelets are colonial.

Evolution and distribution

Traditionally, the auks were believed to be one of the earliest distinct charadriiform lineages due to their characteristic morphology. However, genetic analyses have demonstrated that these peculiarities are the product of strong natural selection instead: as opposed to, for example, plovers, auks radically changed from a wading shorebird to a diving seabird lifestyle. Thus, today, the auks are no longer separated in their own suborder, but are considered part of the Lari suborder which otherwise contains gulls and similar birds. Judging from genetic data, their closest living relatives appear to be the skuas, with these two lineages separating about 30 million years ago. Alternatively, auks may have split off far earlier from the rest of the Lari and undergone strong morphological, but slow genetic evolution, which would require a very high evolutionary pressure, coupled with a long lifespan and slow reproduction.
The earliest unequivocal fossils of auks are from the late Eocene, some 35 mya. The genus Miocepphus, is the earliest known from good specimens. Two very fragmentary fossils are often assigned to the Alcidae, although this may not be correct: Hydrotherikornis and Petralca. Most extant genera are known to exist since the Late Miocene or Early Pliocene. 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 that it was there they first evolved, and it is in the Miocene Pacific that the first fossils of extant genera are found. Early movement between the Pacific and the Atlantic probably happened to the south, 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 includes in the family Alcidae under some definitions. One species, Miomancalla howardae, is the largest charadriiform of all time.
s are true auks only found in the Atlantic Ocean
The extant auks are broken up into 2 main groups: the usually high-billed puffins and auklets, as opposed to the more slender-billed murres and true auks, and the murrelets and guillemots. The tribal arrangement was originally based on analyses of morphology and ecology. mtDNA cytochrome b sequence 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 there are only a few species in each. This is probably a product of the rather small geographic range of the family, and the periods of glacial 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 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 upwellings. The current paucity of auks in the Atlantic, compared to the Pacific is considered to be because of extinctions to the Atlantic auks; the fossil record shows there were many more species in the Atlantic during the Pliocene. Auks also tend to be restricted to continental shelf waters and breed on few oceanic islands.
Hydotherikornis oregonus, the oldest purported alcid from the Eocene of California, is actually a petrel and is reassigned to the tubenoses. A 2003 paper entitled "The Earliest North American Record of Auk From the Late Eocene of Central Georgia" by Robert M. Chandler and Dennis Parmley of Georgia College and State University reports a Late Eocene, wing-propelled diving, auk from the Priabonain Stage of the Late Eocene. These sediments have been dated through Chandronian NALMA, 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 are tropical or sub-tropical as evidenced by a wealth of warm water shark teeth, palaeophied snake vertebrae and turtles.

Systematics

Biodiversity of auks seems to have been markedly higher during the Pliocene. See the genus accounts for prehistoric species.