Northern Gannet

Northern Gannet

The northern gannet (Morus bassanus) is a seabird and it is the largest member of the gannet family, Sulidae. It has the same colours as the Australasian gannet and is similar in appearance. Nesting in colonies as large as 60,000 pairs on both sides of the north Atlantic this bird undertakes seasonal migrations and is a spectacular high-speed diver. Old names for the northern gannet include solan and solan goose. Adults are 81–110 cm (32–43 in) long, weigh 2.2–3.6 kg (4.9–7.9 lb) and have a 165–180 cm (65–71 in) wingspan. Before fledging, the immature birds (at about 10 weeks of age) can weigh more than 4 kg (8.8 lb). Each wing measures between 47 and 53 cm when outstretched and the beak measures between 9 and 11 cm (measured from the head). The two sexes are a similar size. The plumage of the adults is white with dark wing tips, with colours that range from brown to black.

The colour of the head, cheeks and side of the neck depends on the season and the individual, during breeding, the head and neck are brushed in a delicate yellow. Although this colouring may not be evident in some individuals. The feathers are waterproof, which allows the birds to spend long periods in water. A water impermeable secretion produced by a sebaceous gland covers the feathers and the birds spread it across their body using their beak or their head. The eye is light blue, and it is surrounded by bare, black skin, which gives the birds their characteristic facial expression. Fledglings are brown with white wing tips. They have white spots on their head and on their back and a v-shaped white area underneath.

The plumage of year-olds can be almost completely brown, in the second year the birds’ appearance changes depending on the different phases of moulting: they can have adult plumage at the front and continue to be brown at the rear. They gradually acquire more white in subsequent seasons until they reach maturity after five years. Newborn chicks are featherless and are dark blue or black in colour. In the second week of life they are covered in white down. From the fifth week they are covered in dark brown feathers flecked with white. Their beak is long, strong and conical with a slight downward curve at the end.

The front part has a sharp edge. In adults, the beak is blue-grey with dark grey or black edges. It is brownish in immature birds. The northern gannet’s eyes are large and point forwards, they have a light blue to light grey iris surrounded by a thin black ring. The four toes of their feet are joined by a membrane that can vary from dark grey to dark brown. There are yellow lines running along the toes that continue along their legs, these lines probably have a role in mating.[4] The rear toe is strong and faces inwards allowing the birds to firmly grip onto vertical cliff faces. Northern gannets dive vertically into the sea at velocities of up to 100 km/h and the structure of their bodies is adapted for this practice. They do not have external nostrils and their secondary nostrils can be closed when they are in water.

The opening of their auditory canal is very small and is covered with feathers, they can also be closed in water using a system that is similar to that used for the nostrils. The sternum is very strong and sufficiently long to provide protection for the internal organs from impacts with water. The lungs are highly developed and probably also play a role in reducing the effects of hitting water at high speeds and protect the body from these effects. There are subcutaneous air sacks in the lower body and along the sides. Other air sacks are located between the sternum and the pectoral muscles and between the ribs and the intercostal muscles.

These sacks are connected to the lungs and are filled with air when the bird breathes in. The air can be expelled by muscle contractions. Individuals have a subcutaneous fat layer, dense down and tightly overlapping feathers that help them withstand low temperatures. A reduced blood flow in the webbing on their feet outside of the breeding season also helps to maintain body temperature when they swim.



The wings of the northern gannet are long and narrow and they 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 55 and 65 km/h even though their flying muscles are not as highly developed as in other birds where they represent around 20% of total weight, in northern gannets the flying muscles are less than 13%. The consequence of this is that northern gannets need to warm up before they begin flying. They also walk with difficulty and this means that they have difficulty taking off 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. They take advantage of the wind produced by the front of a wave in the same way as the albatross does. They are only seen inland when they have been blown off-course by storms. They alight on water with their feet retracted. They rarely land on water with their feet stretched forward like pelicans or cormorants. When they are on the water their body is rather low in the water with their tail pointing diagonally upwards. They alight with difficulty on land and often alight with a bump as their narrow wings do not allow them to turn easily and they have to use their feet and tail to aid in these manoeuvres. Individuals often suffer damage to their legs or feet when they land on the ground if there is not sufficient wind.

Damaged or broken wings are a frequent cause of death in adults.[14] The position of the legs towards the rear of the body means that they walk in a similar way to ducks. The northern gannet does not have a very characteristic acoustic repertory. Its typical call is rab-rab-rab, which is emitted when fishing and also when on the nest. They have a special call when they approach the colony, this call is often heard because there is usually a lot of toing and froing in a colony. Males and females make similar calls. Their breeding range is the North Atlantic on coasts influenced by the Gulf Stream. The exception being the colonies of the Gulf of Saint Lawrence and the islands off the east coast of Canada. They normally nest in large colonies, on cliffs overlooking the ocean or on small rocky islands. The waters near to these cliffs have a summer temperature at the surface of between 10 and 15 °C. the water temperature determines the distribution of Atlantic mackerel and herring, which are the main food source for the northern gannet.

For this reason there is a close relationship between the location of northern gannet breeding colonies and the distribution of these fish. Northern gannet colonies can be found in the far north in regions that are very cold and stormy. The ornithologist Bryan Nelson has suggested that they can survive in these regions due to a number of factors including: the combination of body weight and a strong beak that allows them to capture strong muscly fish and the ability to dive to great depths and capture prey far from the cliffs. In addition they are able to stand long periods without eating owing to their large fat reserves. The northern limit of their breeding area depends on the presence of waters that are free of sea ice during the breeding season. Therefore, while Greenland and Spitsbergen offer suitable breeding sites, the arctic regions have summers that are too short to allow the northern gannets to lay their eggs and raise a brood, which required between 26 and 30 weeks.

 The southern limit of their distribution mainly depends on the presence of sufficient prey. The species is a rare visitor in the Black Sea region. According to the ornithologist Bryan Nelson northern gannets can recognize the call of their breeding partner, chicks and birds in neighbouring nests. Individuals from outside this sphere are treated with more aggression. Some breeding colonies have been recorded as being located in the same place for hundreds of years. The cliffs containing the colonies appear to be covered in snow when seen from a distance, due to the number of nests present on them.

There is a written record of a colony on the island of Lundy from 1274. It noted that the population was declining due to hunting and the theft of eggs. The colony finally disappeared in 1909. 68% of the world population breeds around the coasts of Great Britain and Ireland. The biggest colonies include: Bass Rock off the east coast of Scotland, first recorded in 1448. In 2004 it contained more than 48 000 nests. This is where part of the species’ Latin name comes from. Saint Kilda and Sula Sgeir, in the Hebrides. Saint Kilda is the largest colony in Europe with more than 60 000 nests. Eldey off Iceland, where between 14 000 and 15 000 pairs breed. Other European colonies are found in the south west of Ireland, and off the west (Runde Island) and north of Norway (Syltefjord, Hovflesa and Storstappen).

The most southerly European colony is on the island of Rouzic off the French Atlantic coast. There are breeding colonies along the coast of Newfoundland and on the islands in the Gulf of Saint Lawrence. The largest colony has 32 000 nests and is on Bonaventure Island off the south coast of Quebec. A 2004 survey counted 45 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. This increase in numbers could also be due to northern gannets benefiting from the growing activities of deep sea fishing. In 1992 the International Union for the Conservation of Nature (IUCN) estimated the bird’s population to be some 526 000 However, taking into account an estimate produced for BirdLife International in 2004 of the European population the IUCN revised its global population to between 950 000 and 1 200 000 individuals.



Northern gannets forage for food during the day, generally by diving 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 320 km 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 280 and 320 km away. It is likely that they fly greater distances than this while searching for food, possibly up to double this distance, however, they normally fly less than 150 km.

When feeding, these birds are spectacular high-speed divers, they can locate their prey from heights of up to 45 metres, but they normally search from a height of between 10 and 20 m. When they see a fish they will dive into the water. They dive with their bodies straight and rigid, wings tucked close to the body but reaching back, extending beyond the tail, before piercing the water like an arrow. They control the direction of the dive using their wings. Just as it is going to hit the water a bird will fold its wings against its body. A bird’s head and neck are stretched out in front of the body and the beak is shut. Birds can hit the water at speeds of up to 100 km/h.

This allows them to penetrate 3–5 m (10–16 ft) below the surface, and occasionally they will swim down to 12–15 m (40–50 ft). They eat mainly fish 2.5–30.5 cm (0.98–12.01 in) in length which 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 eaten. In the case of the larger fish species northern gannets will only eat the young fish. They will also follow fishing boats with the hope of finding food in the same was as gulls do. They fly around the boats to steal fish from the fishing nets or pick up the remains thrown into the sea.

The oldest birds are the first to return to the breeding colonies. The exact duration of the breeding season depends on the colony’s geographic location: the breeding season on Bass Rock starts in the middle of January, that of Iceland at the end of March or in April.[42] The birds that are not of breeding age arrive a few weeks later. In general, birds first return to a colony (not necessarily the one they were born in) when they are two or three years old. It is not unusual for birds to change colony before they reach breeding age, but once an individual has successfully bred in a colony it will not change to another. Immature birds stay on the edges of the colony.

They may even make a nest but they will not breed until they are four or five years old. Some birds of this age will occupy empty nests that they will aggressively defend if they have sat on them for two or three days. If an apparently empty nest has an owner the immature bird will abandon it without putting up a struggle when the owner arrives to claim the nest.


The preferred nesting sites are on coastal hillsides or cliffs If these sites are not available northern gannets will nest in groups on islands or flat surfaces. As they find it more difficult to take off from these locations they will often cross the area occupied by an adjacent nest causing an aggressive reaction from the pair occupying that nest, this means that the stress levels are higher in this type of colony than in those on more vertical surfaces. Notwithstanding this, nests are always built close together and ideal nesting sites will not be used if they are some distance from a colony. On average there are 2.3 nests per square metre.

Nests are made from seaweed, plants, earth and all types of object that float on the sea. The males usually collect the materials. Nests measure between 50 and 70 cm in diameter and are some 30 cm in height, during the course of a breeding season they will sustain damage from the wind and other causes and they require frequent maintenance. The area a nest occupies grows throughout the breeding season as the breeding pairs throw their excrement outside the nest. A female will not react if a male approaches her nest, but she will defend it fiercely if another female approaches. Northern gannets exhibit many types of aggressive behaviour while they are nesting. Confrontations normally only take place between birds of the same sex. Females will lower their heads before an aggressive male that is defending its nest, this will expose the back of the female’s neck and the male will take it in its beak and expel the female from the nest.

A female will not react if a male approaches a nest but it will react fiercely if another female approaches. The fights between males that occupy nests for the first time are particularly intense. Such fights can lead to serious injuries. The fights are preceded by threatening gestures, which are also seen outside the breeding season. Males will demonstrate ownership of a nest by gesturing towards their neighbours with their head with the beak pointing down and the wings slightly outstretched. Once males have found a place to breed they try to attract an available female. The females will fly over the colony a number of times before landing. Their posture, with the neck stretched out, tells the male that they are available for courtship.

The male will then shake their heads in a similar way to when they are guarding their nest but with their wings closed. They usually push their prey deeper into the water and capture it as they return to the surface. When a dive is successful, gannets 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 bird’s subcutaneous air bags aid their rapid return to the surface. 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.

Northern gannets also forage for fish while swimming with their head under water. Some studies have found that the duration and direction of flights made while foraging for food are similar for both sexes. However, 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




Key Words: animal, animalia, aves, avian, chordata, aves, Suliformes, northern gannet, Morus bassanus, Sule, Basstölpel, Alcatraz Atlántico, suula, Fou de Bassan, Súla, Sula bassana, shirokatsuodori, Jan-van-gent, Havsule, gluptak, Havssula, sula biela, Ganso-patola, bird, seabird, Sulidae, high-speed diver, solan goose, sebaceous gland, Bass Rock, Helgoland, Saint Kilda, Sula Sgeir, Eldey Iceland, Runde, Newfoundland, Gulf of Saint Lawrence, Bonaventure Island, monogamous, bird, vogel, oiseau, wildlife, wildlifepics, dennis, binda, dabinda
 

  

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