Extinct Genera, see Systematics
- This article is about a family of birds. For the American ornithological journal, see The Auk.
Auks are birds of the family Alcidae in the order Charadriiformes. They are superficially similar to penguins due to their black-and-white colours, their upright posture and some of their habits. Nevertheless they are not related to the penguins at all, but considered by some to be a product of moderate convergent evolution.
In contrast to penguins, the modern auks are able to fly (with the exception of the recently extinct Great Auk). They are good swimmers and divers, but their walking appears clumsy. Due to their short wings auks have to flap their wings very fast in order to fly.
Auks live on the open sea and only go ashore for breeding, although some species, like the Common Guillemot, spend a great part of the year defending their nesting spot from others.
Several species have different names in Europe and North America. The guillemots of Europe are murres in North America, if they occur in both continents, and the Little Auk becomes the Dovekie.
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, molecular 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 molecular data, their closest living relatives appear to be the skuas, with these two lineages separating about 30 MYA (Paton et al., 2003). This may or may not be correct due to uncertainties of the fossil record (Thomas et al., 2004, and see below). Alternatively, auks may have split off far earlier from the rest of the Lari and undergone strong morphological, but slow molecular 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 Miocene (e.g. the genus Miocepphus, 15 MYA). Two very fragmentary fossils are often assigned to the Alcidae, although this may not be correct: Hydrotherikornis (Late Eocene, some 35 MYA) and Petralca (Late Oligocene). Most extant genera are known to exist since the Late Miocene or Early Pliocene (c. 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 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 (since there was no northern opening to the Atlantic), later movements across the Arctic Sea (Konyukhov, 2002). The flightless subfamily Mancallinae which was apparently restricted to the Pacific coast of southern North America became extinct in the Early Pleistocene.
The extant auks (subfamily Alcinae) are broken up into 2 main groups: the usually high-billed puffins (tribe Fraterculini) and auklets (tribe Aethiini), and the more slender-billed murres (tribe Alcini) and the murrelets and guillemots (tribes Brachyramphini and Cepphini). Molecular studies (Friesen et al., 1996; Moum et al., 2002) confirm this arrangement except that the Synthliboramphus murrelets should be split into a distinct tribe, as they appear more closely related to the Alcini.
Compared to other families of seabirds, there are no genera with many species (such as the 47 Larus gulls). 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 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 (which along with krill are the auk's principal food items) can swim doubles as the temperature increases from 5°C to 15°C, 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 (6 species), compared to the Pacific (19-20 species) 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.
Feeding and ecology
The feeding behaviour of auks is often compared to that of penguins; they are both wing-propelled pursuit divers. In the region where auks live their only seabird competition is with cormorants (which dive powered by their strong feet); in areas where the two groups feed on the same prey the auks tend to feed further offshore.
Although not to the extent of penguins, auks have to a large extent sacrificed flight, and also mobility on land, in exchange for swimming; 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 (including the Razorbill) and murrelets being the most efficient under the water, whereas the puffins and auklets are better adapted for flying and walking. This reflects the type of prey taken; 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 between 30 m for the auklets.
Social behaviour and breeding
The majority of auk species are colonial, nesting in anything between small groups to large thousand strong colonies. As well as possible advantages for defence against predators, there is a benefit in terms of foraging to being colonial; birds that see a neighbour returning with food will set off to forage in the direction it came from. Two species, the Marbled Murrelet and the Kittlitz's Murrelet are solitary nesters, choosing old growth forest and high mountains respectively. In these areas the benefits of colonial nesting would be outweighed by the presence of terrestrial predators (foxes and raccoons, for example) which island and cliff breeding auks do not have to deal with.
Nesting sites in colonies can vary from nothing more than a patch on a cliff face, to natural crevices in the rocks and boulders, to burrows dug by the bird. Many nesting sites are attended nocturnally, in some cases as the adults are likely to fall victim to kleptoparasitism (such as the Rhinoceros Auklet) or because the adults themselves are likely prey items (like the Cassin's Auklet). Mating itself can happen both on the colony, as happens with the Razorbill and Little Auk, or at sea, as is the case for puffins and auklets.
- Hydrotherikornis (fossil, disputed)
- Subfamily Petralcinae (fossil,
- Subfamily Alcinae
- Miocepphus (fossil)
- Tribe Alcini - Auks and murres
- Common Guillemot or Common Murre, Uria aalge
- Brunnich's Guillemot or Thick-billed Murre, Uria lomvia
- Little Auk or Dovekie, Alle alle
- Great Auk, Pinguinus impennis (extinct, c.1844)
- Razorbill, Alca torda
- Tribe Synthliboramphini -
- Xantus's Murrelet, Synthliboramphus hypoleucus - sometimes separated in Endomychura
- Craveri's Murrelet, Synthliboramphus craveri - sometimes separated in Endomychura
- Ancient Murrelet, Synthliboramphus antiquus
- Japanese Murrelet, Synthliboramphus wumizusume
- Tribe Cepphini - True guillemots
- Black Guillemot or Tystie, Cepphus grylle
Pigeon Guillemot, Cepphus columba
- Kurile Guillemot, Cepphus (columba) snowi
- Spectacled Guillemot, Cepphus carbo
- Tribe Brachyramphini - Brachyramphine
Marbled Murrelet, Brachyramphus
- Long-billed Murrelet Brachyramphus (marmoratus) perdix
- Kittlitz's Murrelet, Brachyramphus brevirostris
- Marbled Murrelet, Brachyramphus marmoratus
- Tribe Aethiini - Auklets
- Cassin's Auklet, Ptychoramphus aleuticus
- Parakeet Auklet, Aethia psittacula
- Crested Auklet, Aethia cristatella
- Whiskered Auklet, Aethia pygmaea
- Least Auklet, Aethia pusilla
- Tribe Fraterculini - Puffins
- Rhinoceros Auklet, Cerorhinca monocerata
- Atlantic Puffin, Fratercula arctica
- Horned Puffin, Fratercula corniculata
- Tufted Puffin, Fratercula cirrhata
Biodiversity of auks seems to have been markedly higher during the Pliocene (Konyukhov, 2002). See the genus accounts for prehistoric species.
- Collinson, Martin (2006): Splitting headaches? Recent taxonomic changes affecting the British and Western Palaearctic lists. Brit. Birds 99(6): 306-323. HTML abstract
- Friesen, V. L.; Baker, A. J. & Piatt, J. F. (1996): Phylogenetic Relationships Within the Alcidae (Charadriiformes: Aves) Inferred from Total Molecular Evidence. Molecular Biology and Evolution 13(2): 359-367. PDF fulltext
- Gaston, Anthony & Jones, Ian (1998): The Auks, Alcidae. Oxford University Press, Oxford. ISBN 0-19-854032-9
- Konyukhov, N. B. (2002): Possible Ways of Spreading and Evolution of Alcids. Izvestiya Akademii Nauk, Seriya Biologicheskaya 5: 552–560 [Russian version]; Biology Bulletin 29(5): 447–454 [English version]. DOI:10.1023/A:1020457508769 (Biology Bulletin HTML abstract)
- Moum, Truls; Arnason, Ulfur & Árnason, Einar (2002): Mitochondrial DNA Sequence Evolution and Phylogeny of the Atlantic Alcidae, Including the Extinct Great Auk (Pinguinus impennis). Molecular Biology and Evolution 19(9): 1434–1439. PDF fulltext
- Paton, T. A.; Baker, A. J.; Groth, J. G. & Barrowclough, G. F. (2003): RAG-1 sequences resolve phylogenetic relationships within charadriiform birds. Molecular Phylogenetics and Evolution 29: 268-278. DOI:10.1016/S1055-7903(03)00098-8 (HTML abstract)