The razorbill (Alca torda) is a North Atlantic colonial seabird and the only extant member of the genus Alca of the family Alcidae, the auks. It is the closest living relative of the extinct great auk (Pinguinus impennis). Historically, it has also been known as "auk", "razor-billed auk" and "lesser auk".

Razorbills are primarily black with a white underside. The male and female are identical in plumage; however, males are generally larger than females. This agile bird, which is capable of both flight and diving, has a predominantly aquatic lifestyle and only comes to land in order to breed. It is monogamous, choosing one partner for life. Females lay one egg per year. Razorbills nest along coastal cliffs in enclosed or slightly exposed crevices. The parents spend equal amounts of time incubating, and once the chick has hatched, they take turns foraging for their young.

Presently, this species faces major threats, including the destruction of breeding sites, oil spills, and deterioration of food quality. As a result, razorbills have on occasion been seen outside of their normal range as they search for alternative food sources. The IUCN records the population of the species as fluctuating. and appears to be increasing or stable at the present. The genus name Alca is from Norwegian Alke, and torda is from törd a Gotland Swedish dialect word; both terms refer to this species. The type locality is Stora Karlsö, just off the west coast of Gotland, Sweden. The word Alca had been used for the razorbill by earlier authors such as Carolus Clusius in 1605 and Francis Willughby in 1676.

The razorbill (Alca torda) is the sole living species in the genus Alca. Its close relative, the great auk (Pinguinus impennis), which became extinct in the mid-19th century, was also formerly included in the genus Alca.

  • Alca sp. (Late Miocene/Early Pliocene of Lee Creek Mine, US) - possibly A. stewarti
  • Alca stewarti (Kattendijk Sands Early Pliocene of Belgium)
  • Alca ausonia (Yorktown Early Pliocene of Lee Creek Mine, US - Middle Pliocene of Italy)
  • Alca sp. (Puerto de Mazarrón Pliocene of El Alamillo, Spain) - may be A. antiqua or A. ausonia

As far as is known, the genus Alca seems to have evolved in the western North Atlantic or the present-day Caribbean like most other Alcini. Its ancestors would have reached these waters through the still-open Isthmus of Panama during the Miocene. and reduced to subspecies by Salomonsen in 1944), is no longer accepted because the distinguishing characteristic, an additional furrow in the upper mandible, is now known to be age-related. and some moving south as far as the western Mediterranean. Approximately 60 to 70% of the entire razorbill population breeds in Iceland.

  • Grímsey, Iceland (66°33' N)
  • Látrabjarg, Iceland (65°30' N) - 230,000 pairs, about 40% of the global population (mid-1990s estimate). Breeding season June – July.
  • Farne Islands, Northumberland, UK (55°38' N) - 523 pairs in 2022, breeding season May to mid-July.
  • Bempton Cliffs, East Riding of Yorkshire, UK (54°14' N) - 30,673 pairs in 2022, pairs from March to mid-July.
  • Skomer Island, Pembrokeshire, Wales.
  • Heligoland, Germany (54°10' N) - a few pairs only.
  • Gannet Islands, Canada (53°58' N) - 9,800 pairs.
  • Baccalieu Island, Canada (48°07' N).
  • Witless Bay, Canada (47°13' N).
  • Cape St. Mary's, Canada (46°49' N).

Behaviour

thumb|Taking off from water

The life-history traits of the razorbill are similar to that of the common murre. However, razorbills are slightly more agile. In North America it is a largely migratory seabird, as during the colder months, it leaves land and spends the entire winter in the waters of the Atlantic Ocean, though western European birds often remain close to their breeding sites.

During breeding, both males and females protect the nest. Females select their mate and will often encourage competition between males before choosing a partner. Although gregarious in breeding colonies, nests are not contiguous, but some metres apart, resulting in less aggression than in Guillemot colonies.

Feeding

Razorbills dive deep into the sea using their semi-folded wings and their streamlined bodies to propel themselves toward their prey. They keep their feet spread. While diving, they rarely stay in groups but rather spread out to feed. The majority of their feeding occurs at a depth of but they have the ability to dive up to below the surface.

Conservation and management

thumb|Razorbills on [[Machias Seal Island Migratory Bird Sanctuary]]

In the early 20th century, razorbills were harvested for eggs, meat, and feathers. This greatly decreased the global population. In the USA, they were finally protected by the 1917 Migratory Bird Treaty Act which reduced hunting.