The Northern gannet (Morus bassanus) is a seabird, the largest species of the gannet family, Sulidae. It is native to the coasts of the North Atlantic Ocean, breeding in Western Europe and Northeastern North America. It is the largest seabird in the northern Atlantic. The sexes are similar in appearance. The adult northern gannet has a mainly white streamlined body with a long neck, and long and slender wings. It is long with a wingspan. The head and nape have a buff tinge that is more prominent in breeding season, and the wings are edged with dark brown-black feathers. The long, pointed bill is blue-grey, contrasting with black, bare skin around the mouth and eyes. Juveniles are mostly grey-brown, becoming increasingly white in the five years it takes them to reach maturity.

Nesting takes place in colonies on both sides of the North Atlantic, the largest of which are at the Bass Rock (75,000 pairs as of 2014), St. Kilda (60,000 pairs as of 2013) and Ailsa Craig (33,000 pairs as of 2014) in Scotland, in Ireland (Sceilg Bheag; little Skellig, 35,000 pairs in 2011), Grassholm in Wales, and Bonaventure Island (60,000 pairs in 2009) off the coast of Quebec. Its breeding range has extended northward and eastward, with colonies being established on Russia's Kola Peninsula in 1995 and Bear Island (the southernmost island of Svalbard), in 2011. Colonies are mostly located on offshore islands with cliffs, from which the birds can more easily launch into the air. The northern gannet undertakes seasonal migrations and catches fish (which are the mainstay of its diet) by making high-speed dives into the sea up to 60 mph.

The northern gannet was previously hunted for food in certain parts of its range, and although that practice still continues in the Outer Hebrides of Scotland and the Faroe Islands, the bird faces few other natural or man-made threats. Since its population is growing, the International Union for Conservation of Nature considers it a least-concern species. Because it is both a conspicuous and a common bird, it is referred to in several ancient myths and legends.

Taxonomy

The Swiss naturalist Conrad Gessner gave the northern gannet the name Anser bassanus or scoticus in the 16th century, and noted that the Scots called it a solendguse. The former name was also used by the English naturalist Francis Willughby in the 17th century; the species was known to him from a colony in the Firth of Forth and from a stray bird that was found near Coleshill, Warwickshire. It was one of the many species originally described by the Swedish zoologist Carl Linnaeus in the landmark 1758 10th edition of his Systema Naturae, where it was given the binomial name Pelecanus bassanus. The French biologist Brisson placed it in the genus Sula in 1760, and his compatriot Louis Pierre Vieillot moved the species to his new genus Morus in 1816. Morus is derived from Ancient Greek , meaning , and refers to the lack of fear shown by breeding gannets and boobies, which enables them to be easily killed. The specific name bassanus is from the Bass Rock in the Firth of Forth. The ornithologist Bryan Nelson in 1978 supported the species' inclusion in Sula as he felt the differences in anatomy, behaviour, ecology and morphology between gannets and boobies were not sufficient to warrant separate genera.

Charles Lucien Bonaparte described the American populations as Sula americana in 1838, though the basis for distinguishing them from the European species was unclear and the name is now considered to be a synonym.

"Northern gannet" has been designated as the official English common name for the species by the International Ornithologists' Union (IOC). It is also known as the North Atlantic gannet. Gannet is derived from Old English ganot, meaning "strong or masculine", which is ultimately from the same Old Germanic root as gander. Soland goose and similar old names for the northern gannet such as solan or solan goose derive from a hypothetical Scottish Gaelic sulan, itself borrowed from the Old Norse . The literal meaning is "cleft stick", referring to the appearance of the conspicuous crossed black wing tips on a perched northern gannet. Old regional names such as Norfolk's "herring gant" or Yorkshire's "mackerel gant" refer to typical fish prey. Lincolnshire's gaunt, although derived from the same Germanic root, usually applies to the great crested grebe, but the English writer Richard Hakluyt used the term in 1600 to refer to the gannet, "a great White foule". Young birds have been called "spotted booby" or "parliament goose", the former term referring to their plumage. The feeding habits of the gannet have led to its name being used as slang for a gluttonous person, a usage first recorded in 1929. A 2011 genetic study of nuclear and mitochondrial DNA suggests that the ancestor of the gannets arose around 2.5 million years ago before splitting into northern and southern lineages. The latter then split into the Cape and Australasian gannets around 0.5 million years ago. The three gannets are generally considered to be separate species forming a superspecies, though they have also formerly been classified as subspecies of Sula bassanus.

Description

An adult northern gannet has a wingspan, and is long and weighs ,

The beak is long, strong and conical with a slight downcurve at the end and a sharp cutting edge. In adults, the beak is blue-grey with dark grey or black edges. There is a black groove running the length of the mandible that merges into the skin around the eyes. A black band of bare skin also separates the pale feathers of the forehead and throat from the bill, which gives the gannet its distinctive face markings. The four-toed feet are joined by a membrane that can vary in colour from dark grey to dark brown. There are coloured lines running along the toes that continue along up the legs. These are typically greenish-yellow in males and bluish in females and probably have a role in mating.

Breeding colonies

alt=Bass Rock, Scotland|thumb|upright=1.3|[[Bass Rock in the Firth of Forth, Scotland, is the world's largest colony.]]

Some northern gannet breeding colonies have been recorded as being located in the same place for hundreds of years. The cliffs containing the colonies appear white when seen from a distance, due to the number of nesting birds present on them. There is a written record of a colony on the island of Lundy from 1274. There were only 70 nests by 1871, and the colony finally disappeared by 1909 at the latest. More than two-thirds of the world population breeds around the coasts of the British Isles. Colonies include:

  • Scotland

:* Bass Rock, in the Firth of Forth, first recorded in 1493. In 2004, it contained more than 48,000 nests. By 2014 this had increased to over 75,000, making it the largest colony in the world.

:* Northern gannets began a colony at Troup Head in Aberdeenshire in 1988, and by 2014 it held an estimated 6,456 pairs.<!-- cites previous 3 sentences --> Ailsa Craig has been known as a colony since 1583.

:* In Shetland, there were an estimated 25,580 breeding pairs at Hermaness, 11,786 on Noss, and 3,591 on Fair Isle in 2013, while Orkney had an estimated 4,550 pairs at Sule Stack. Sule Skerry's breeding population rose from 57 to 1,870 pairs between 2003 and 2013.

  • France. The French island of Rouzic in the Jentilez archipelago off the coast of Brittany hosts the southernmost breeding colony of northern gannets. Established in the late 1930s, it had grown to over 11,500 breeding pairs by 1995. Pairs have nested sporadically with varying success along the Mediterranean coast.
  • Italy. A pair raised a chick successfully for three successive seasons from 2013 to 2015 on a moored boat at Porto Venere in northern Italy, after birds had been seen there since 1993. although that had risen to 2,500 pairs by 2014.
  • Iceland. Eldey, a small island located about off the coast of the Reykjanesskagi Peninsula, Iceland, hosting around 16,300 breeding pairs in 1962, and a similar number in 2008. Iceland has several small colonies along its coast, and on Grimsey, around north.
  • Norway. As of 2016, there are an estimated 6,900 breeding pairs in Norway.

Migration

After the breeding season, adult northern gannets disperse over a wide area although they travel no more than from the breeding colony. It is not known if all birds from one colony migrate to the same over-wintering area. Many adults migrate to the west of the Mediterranean, passing over the Strait of Gibraltar and flying over land as little as possible. Other birds follow Africa's Atlantic coastline to arrive in the Gulf of Guinea. Immature northern gannets from colonies in Canada fly to the Gulf of Mexico, much further south than the adults.

The immature gannets migrate southwards for great distances and have been recorded as far south as Ecuador. In their second year some birds return to the colony in which they were born, where they arrive later than the mature birds. They then migrate south again at the end of the breeding season, but travel shorter distances in this second migration. One individual was found to have travelled from its colony in Alderney to Scandinavian waters, a round trip of around .

The species has been recorded as a vagrant in many central and eastern European countries as far south and west as the Black Sea, and also in Bermuda, Cuba, Cyprus, Egypt, Kazakhstan, Jan Mayen and Syria.

Behaviour

thumb|Plunge-diving with wings retracted

The wings of the northern gannet are long and narrow and are positioned towards the front of the body, allowing efficient use of air currents when flying. Even in calm weather they can attain velocities of between although their flying muscles are relatively small: in other birds, flying muscles make up around 20% of total weight, while in northern gannets the flying muscles are less than 13%. Despite their speed, they cannot manoeuvre in flight as well as other seabirds. Northern gannets need to warm up before flying. They also walk with difficulty, and this means that they have problems getting airborne from a flat area. They take off from water by facing into the wind and strongly beating their wings. In light winds and high waves they are sometimes unable to take off, and they can become beached.

Northern gannets alight on land using angled wings, fanned tail and raised feet to control their speed, not always successfully, since damaged or broken wings were recorded as a frequent cause of death in adults at one colony.

Feeding

Northern gannets forage for food during the day, generally by diving at high speed into the sea. They search for food both near to their nesting sites but also further out to sea. Birds that are feeding young have been recorded searching for food up to from their nest. It has been found that 2% of birds nesting in the colony on Bass Rock search for fish at Dogger Bank, between away. It is likely that they fly further than this while foraging, possibly up to double the distance; normally they fly less than . Some studies have found that the duration and direction of flights made while foraging for food are similar for both sexes, although there are significant differences in the search behaviour of males and females. Female northern gannets are not only more selective than males in choosing a search area: they also make longer and deeper dives and spend more time floating on the surface than males. They dive with their bodies straight and rigid, wings tucked close to the body but angled back, extending beyond the tail, before piercing the water like an arrow. They control the direction of the dive using their wings and tail, and fold their wings against the body just before impact. Birds can hit the water at speeds of up to . and they will swim down to an average , sometimes deeper than . The bird's subcutaneous air sacs may have a role in controlling their buoyancy.

Gannets usually push their prey deeper into the water and capture it as they return to the surface. When a dive is successful, they swallow the fish underwater before surfacing, and never fly with the fish in their bill. Larger fish are swallowed headfirst, smaller fish are swallowed sideways or tail-first. The fish is stored in a branched bag in the throat and does not cause drag when in flight.

Their white colour helps other gannets to identify one of their kind, and they can deduce the presence of a shoal of fish by this diving behaviour; this in turn facilitates group foraging, which makes capturing their prey easier. The colour also makes the gannet less visible to the fish underneath. Northern gannets also forage for fish while swimming with their head under water.

They eat mainly fish in length that shoal near the surface. Virtually any small fish (roughly 80–90% of their diet) or other small pelagic species (largely squid) will be taken opportunistically. Sardines, anchovies, haddock, smelt, Atlantic cod and other shoal-forming species are also eaten. On the other hand, they profit off of discarded bycatch and processed parts and the reduction in competition if humans are taking predatory fish.

M. bassanus inflicts significant wastage on the northwest Atlantic Salmo salar fishery, but does not actually eat much of them. This makes it difficult to resolve this conflict with the fishing industry in the area, as the only option would be to exterminate the birds, which is ecologically unacceptable.

Breeding

thumb|Transporting material for the nest

The oldest birds are the first to return to the northern gannet's breeding colonies. Where two eggs are found in a nest, this is the result of two females laying an egg in the same nest or one egg being stolen from another nest. Northern gannets will lay a replacement egg if the first is lost. Incubation takes 42 to 46 days, during which time the egg is surrounded by the brooding bird's warm, webbed feet. Just before hatching begins, the brooding bird releases the egg from its feet to prevent the egg from breaking under the adult's weight as the chick breaks it open. This is a frequent cause of death for chicks of birds that are breeding for the first time. The process of breaking the eggshell can take up to 36 hours. The webbed feet are also used to cover the chicks, which are only rarely left alone by their parents. Chicks that are left unattended are often attacked and killed by other northern gannets.

A downy chick|thumb

Newly hatched chicks are featherless and are dark blue or black in colour. In the second week of life they are covered in white down, replaced over the next five weeks by dark brown feathers flecked with white. Young chicks are fed regurgitated semi-digested fish by their parents, who open their mouths wide for their young to fetch the food from the back of their throats. Older chicks receive whole fish. Unlike the chicks of other species, northern gannet chicks do not move about the nest or flap their wings to ask for food: this reduces the likelihood that they will fall from the nest.

The adults feed their offspring for around 13&nbsp;weeks, right up until the time they leave. The young birds fledge between 84 and 97 days old, departing by launching themselves off a cliff and flying—a procedure which is impossible to practice beforehand. If they leave the nest in bad weather, they can be mortally wounded as they can be blown against the rocks. The young birds are attacked by adults if unattended. Once they leave the nest, they stay at sea learning to fish and fly, their flight skills being too poor for them to return to the breeding ledges. Gannet pairs are monogamous and may remain together over several seasons, if not for all of their lives. The pairs separate when their chicks leave the nest, but they bond again the following year. Should one of the pair die, the other bird will find another mate.

Conservation status

thumb|Nests among the rocks. The population of this species appears to be increasing.

A 2004 survey counted 45 gannet breeding colonies and some 361,000 nests. The population is apparently growing between 3% and 5% a year, although this growth is concentrated in just a few colonies. Although northern gannet populations are now stable, their numbers were once greatly reduced due to loss of habitat, removal of eggs and killing of adults for their meat and feathers. In 1939, there were 22 colonies and some 83,000 nests, which means that the populations have increased fourfold since that time.

In 1992, the International Union for Conservation of Nature (IUCN) estimated the bird's population to be some 526,000. The filleted birds are then taken to Stornoway, where each hunter receives 200 skins to give away or sell. The practice was described at length as part of the story in The Blackhouse, a novel by Scottish writer Peter May. The continuing practice of hunting and eating gannets attracts criticism in some quarters. The island's name "Sula Sgeir" itself derives from sula, meaning "gannet", and the Old Norse , a skerry. Other sites that continued hunting into the 20th century were Eldey in Iceland, where the activity ceased in 1939, and Mykines, where small-scale culling still persists. About 500 young are culled for consumption each year in Mykines,

Explanatory notes

Citations

General and cited references

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