Northern Gannet (Morus bassanus)

Northern Gannet

[order] SULIFORMES | [family] Sulidae | [latin] Morus bassanus | [UK] Northern Gannet | [FR] Fou de Bassan | [DE] Basstolpel | [ES] Alcatraz Atlantico | [NL] Jan van Gent

Subspecies

Monotypic species

Physical charateristics

The Northern Gannet is one of three subspecies of Gannet Morus bassanus in the world: the other two occur along the south coast of Africa and in Tasmania and New Zealand. Adult gannets have dazzling white plumage except for narrow grey spectacles and jet black, tapering wingtips. During the breeding season, the head and neck assume a delicate saffron yellow tinge. The eyes are an icy blue, and the bill is blue to grey-blue.

Young gannets in autumn plumage are brown, with many white flecks. With the passing of each season, they become progressively whiter, reaching the complete adult plumage in their fourth or fifth year.

Listen to the sound of Northern Gannet

[audio:http://www.aviflevoland.nl/sounddb/N/Northern Gannet.mp3]

Copyright remark: Most sounds derived from xeno-canto

wingspan min.: 170 cm wingspan max.: 192 cm
size min.: 85 cm size max.: 97 cm
incubation min.: 42 days incubation max.: 46 days
fledging min.: 84 days fledging max.: 46 days
broods: 1   eggs min.: 1  
      eggs max.: 1  

Range

Atlantic Ocean : North

Habitat

Gannetries are located on steep cliffs and small offshore islands. At almost all these sites, land predators cannot reach the nesting birds. An exception is Bonaventure Island, which is inhabited by red foxes. If disturbed, gannets will often desert their nest, particularly if they are nesting for the first time.

The offshore islands and steep cliffs that appeal to gannets have sometimes been selected for lighthouses, and several gannetries were probably abandoned in the 19th and early 20th centuries because lighthouses were built on them.

Reproduction

Male Northern Gannets choose a nest site when they are three, four, or five years old. Courtship involves much formal bowing and spreading of wings. Usually the first breeding season is devoted to courtship and building the nest. Pairs may remain together for years. Established pairs add to nests at the breeding colony, which may still be snow-covered when they arrive.

Occupied year after year, a typical nest grows from a low collection of seaweed, sticks, moss, and debris into a substantial heap of feathers, fish skeletons, and droppings accumulated from many generations of nesters. Nests are usually 600 to 900 mm apart and form regular lines due to the hexagonal shape of each territory, an arrangement that allows the birds to pack the maximum number of nests into a given area.

Between late May and mid-June the female gannet lays a single bluish-white egg in the moss-lined hollow at the top of the nest. The parent birds take turns incubating, or warming the egg to hatch it, with their webbed feet. In the first week of July, the first young gannets emerge from their shells. Grey, naked, and helpless, the chick sprawls in the nest, whining like a puppy. It is tended carefully by its parents, and after about two weeks is covered with a protective coat of soft white down.

Until old enough to take to the ocean and fend for themselves, the young are fed by the parents. The young bird reaches deep into its parent’s throat for its meal of partially digested fish. After a few weeks, the parents regurgitate, or bring up, the partially digested fish near the nest, and the young gannet feeds without further aid.

Plumage begins to appear at about six weeks, and flight feathers are fully grown by September. Only after days of hesitation does the young bird half-fly, half-tumble in its first plunge from the rock ledges to the water below. A fledgling occasionally falls to the rocks and, if uninjured, heads for the ocean. Once in the water, the young gannet may live on body fat for days, until it masters the specialized and difficult art of plunge-diving for food.

Feeding habits

Few seabirds are more spectacular in their fishing methods than this one. The gannet may fly alone or as part of a group, usually cruising 18 to 30 m above the sea. When a gannet sees a fish in the water below, it dives more or less vertically, with partially folded wings and great speed. Its impact with the water may send spray as high as 3 m, and the momentum of its dive is thought to carry the bird below its prey. Swimming strongly with the aid of its large webbed feet, and possibly at times with its wings, the gannet captures its prey. On reaching the surface, or even before, it swallows the fish and takes off to resume the hunt or to return to the gannetry to feed its nestling. A diving gannet is a signal to others cruising nearby that a shoal of fish may be present, and they fly to investigate. On seeing a large shoal, they attack in great numbers.

Gannets do not always dive so spectacularly for food. When a shoal of fish is close to the surface, a bird may rise only about a metre before plunging again. Or it may occasionally beat its way over the surface with its wings and feet, head underwater to see the fish. Northern Gannets feed on herring, mackerel, capelin, sandlance, and squid.

Conservation

This species has a very large range, and hence does not approach the thresholds for Vulnerable under the range size criterion (Extent of Occurrence <20,000 km2 combined with a declining or fluctuating range size, habitat extent/quality, or population size and a small number of locations or severe fragmentation). The population trend appears to be increasing, and hence the species does not approach the thresholds for Vulnerable under the population trend criterion (>30% decline over ten years or three generations). The population size is very large, and hence does not approach the thresholds for Vulnerable under the population size criterion (<10,000 mature individuals with a continuing decline estimated to be >10% in ten years or three generations, or with a specified population structure). For these reasons the species is evaluated as Least Concern.
About 444 000 Northern Gannets nest at 34 colonies on the European side of the Atlantic. There are six colonies in Iceland, with a total of 25 000 pairs. In the British Isles, including Ireland, the Shetland Islands, and the Faeroe Islands, there are 22 Northern Gannet colonies, for a total population of 189 700 pairs. The Northern Gannet became established in Norway in 1946, but there are only five colonies with a total population of 2 300 pairs. There is also a gannet colony in northern France, with 6 000 pairs.

The North American population of Northern Gannets is not very large as seabird populations go. There are approximately 87 900 breeding Gannets on the Atlantic coast of North America, all of which nest at six colonies in the Gulf of St. Lawrence and along the east coast of Newfoundland. Once their young leave the nest, the gannets return south and disperse along the coast from New England to the Gulf of Mexico.
Northern Gannet status Least Concern

Migration

Partially migratory, otherwise dispersive. In west Palearctic some, mainly adults, remain in breeding range latitudes throughout winter, though rare Icelandic inshore waters late October to mid-December. Many perform long southward migration, reaching subtropical and even tropical waters off West Africa; this tendency much stronger in young of year. Main assembly of adults at most British and Irish breeding stations from early January, but month later at St Kilda, Shetland, and Faeroe Islands and 2 months later Iceland. Young leave nest sites before able to fly and begin dispersal by swimming; distances up to 72 km recorded; adults tend to remain some weeks longer. Pre-breeders visit colonies during nesting season, arriving later and departing earlier than adults. Immatures widely dispersed in eastern Atlantic and North Sea spring to autumn, increased later by post-fledging dispersal of juveniles.

Distribution map

Northern Gannet distribution range map

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