Auks or alcids are birds of the family Alcidae in the order Charadriiformes. The alcid family includes the murres, guillemots, auklets, puffins, and murrelets. The family contains 25 extant or recently extinct species that are classified into 11 genera. Auks are found throughout the Northern Hemisphere.
The family name Alcidae comes from the genus name Alca, which was given by Carl Linnaeus in 1758 for the razorbill (Alca torda), from the Norwegian word alke.
Description
Auks are superficially similar to penguins, having black-and-white colours, upright posture, and some of their habits. However, they are not closely related to penguins, but are believed to be an example of moderate convergent evolution. Auks are monomorphic (males and females are similar in appearance).
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 flap their wings very quickly to fly.
Auks have largely sacrificed flight, and mobility on land, for swimming ability, although not to the extent that penguins have. Auk 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.
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 (which are dive-powered by their strong feet). 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 in the case of Uria guillemots, for the Cepphus guillemots and for the auklets.
Breeding and colonies
Auks are pelagic birds, spending the majority of their adult lives on the open sea and going ashore only for breeding, although some species, such as 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 use the nesting site year after year.
Some species, such as the Uria guillemots (murres), nest in large colonies on cliff edges; others, such as 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
thumb|upright|Auks as painted by [[Archibald Thorburn]]
Historically, the auks were believed to be one of the earliest distinct charadriiform lineages due to their characteristic morphology, but genetic analyses have demonstrated that these peculiarities are the product of strong natural selection, instead; as opposed to, for example, plovers (a much older charadriiform lineage), auks radically changed from a wading shorebird to a diving seabird lifestyle. Thus today, the auks are no longer separated in their own suborder (Alcae), 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 (Mya).
thumb|left|[[Razorbills are auks found in the Atlantic Ocean.]]
The family contains 25 extant or recently extinct species that are classified 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.
Further reading
- Diving Birds of North America by Paul Johnsgard