Alcidae

Lore & Background

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.

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 100 m in the case of Uria guillemots, 40 m for the Cepphus guillemots and 30 m for the auklets.

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. 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.

Reader's Guide

Auks are significant as a prime example of moderate convergent evolution with penguins, adapting to a diving seabird lifestyle from a wading shorebird ancestor. Their wings represent a compromise between efficient underwater propulsion and the minimum capability needed for flight, with different subfamilies showing varying degrees of adaptation. The family's restricted geographic range—the most limited of any seabird family—and the periods of glacial advance and retreat have shaped their evolution and distribution. Today, auks are restricted to cooler northern waters, as their pursuit-diving hunting method becomes less efficient in warmer waters where prey swim faster. 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, as the fossil record shows many more species were in the Atlantic during the Pliocene. 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.

Did You Know?

• The word 'auk' is derived from Icelandic álka and Norwegian alka or alke, from Old Norse ālka, from Proto-Germanic *alkǭ.
• The family name Alcidae comes from the genus name Alca, given by Carl Linnaeus in 1758 for the razorbill, from the Norwegian word alke.
• Auks are monomorphic, meaning males and females are similar in appearance.
• The earliest unequivocal fossils of auks are from the late Eocene, some 35 million years ago.

Where Auks and Puffins Sit in the Avian Tree

The family Alcidae, which encompasses auks and puffins, occupies a clearly delineated position within the layered architecture of bird classification. It is nested inside the infraorder Larida, which in turn falls under the suborder Lari—a grouping the source material labels as gulls and allies. That suborder belongs to the order Charadriiformes, a worldwide assemblage of roughly 350 species. Climbing further up the hierarchy, Charadriiformes is placed within the superorder Gruae, the infraclass Neoaves, and the subclass Neognathae. The Neognathae are defined by their keeled sternum, a structural feature that separates them from the flightless ratites of the Palaeognathae. With approximately 11,000 bird species formally described as of 2024—and one estimate suggesting the true count approaches 20,000—Alcidae represents a small but distinct thread woven into an extraordinarily diverse global tapestry of avian life.

Sharing the Larida Neighborhood

Within the infraorder Larida, the family Alcidae shares a taxonomic neighborhood with several other distinctive lineages. Its immediate companions in this grouping include the Stercorariidae (skuas and jaegers), the Laridae (gulls, skimmers, and terns), the Glareolidae (coursers and pratincoles), and the Dromadidae (crab-plover). Together these families constitute the suborder Lari, a cluster the classification system helpfully summarizes as gulls and allies. This arrangement implies a shared evolutionary lineage among birds that, at first glance, might appear quite different in form and ecological role. The parent order Charadriiformes is distributed worldwide and encompasses approximately 350 species in total. The precise boundaries of these groupings, however, remain subject to ongoing revision as genetic data continues to reshape our understanding of how these lineages relate to one another across the tree of life.

A Classification in Constant Motion

The placement of Alcidae within the broader avian tree is far from fixed. The source material explicitly cautions that taxonomy is highly fluid given the advent of DNA analysis, and all numerical figures should be treated as approximate. A particularly notable alternative framework, the Sibley-Ahlquist system, proposes a markedly different arrangement of bird relationships from the one presented in the main text. The 44 orders currently recognized by the IOC represent merely one snapshot of an ongoing scientific conversation. The ratites offer a striking cautionary example of how genetic evidence can upend long-standing groupings: what was traditionally a single order, Struthioniformes, has been broken apart because molecular data revealed the group was not truly monophyletic when tinamous were considered. While no specific reclassification of Alcidae is detailed in the provided material, the general principle holds—our understanding of where auks and puffins fit among their Larida neighbors could shift as new molecular evidence emerges.

A Small Family in a Vast World

The family Alcidae, containing auks and puffins, exists within a global avian community of staggering scale. As of 2024, roughly 11,000 bird species have been formally described, though one estimate places the actual number of species at nearly 20,000. To appreciate the relative size of Charadriiformes, consider that the order passerines (perching birds) alone accounts for well over 5,000 species—vastly exceeding the 350 species found across all of Charadriiformes. The 44 orders recognized by the IOC span every continent and ocean, from the flightless ostriches of Africa to the kiwis of Australasia, from the extinct moas of New Zealand to the living tinamous of South America. Within this enormous diversity, the small family of auks and puffins holds a modest but well-defined niche in the suborder Lari, a group the classification system aptly summarizes as gulls and allies.