Northern gannet
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Northern Gannet ( Morus bassanus ) |
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The northern gannet ( Morus bassanus ) is a goose-sized sea bird from the gannet family . Within this family it is the furthest northern breeding species and the only one that also breeds in Europe. The northern gannet has also been a breeding bird on Heligoland since 1991 . Large colonies in which several thousand breeding pairs raise their respective young are typical of the northern gannet. Northern gannets prefer to build their nests on steep rocky islands off the coast.
Like most gannet species, the northern gannet has opened up a food niche in which it competes with only a few other species. Its preferred prey fish are fatty fish such as herrings and mackerel. Within the order of the Suliformes it moves furthest away from its breeding colony during its foraging. Only the gray-footed booby has a comparable flight performance during food acquisition . The northern gannet is a shock diver who plunges into the sea in a rapid dive to hunt for fish. Its anatomical features include a streamlined body, long, narrow wings, a finely toothed beak in the front half and large webbed feet.
Surname
The large breeding colony on the rocky island of Bass Rock off the Scottish coast , which was mentioned in documents as early as 1448, gave rise to the German term gannet.
Seafarers referred to birds of this family in Portuguese as "bobo" or "fool" because the seabirds liked to land on ships and because of their familiarity there were often easy but tasty prey for seafarers. Even in their breeding colonies, the birds show hardly any fear and are therefore very easy to catch. The generic name Morus comes from the ancient Greek moros, also meaning stupid, stupid.
Derived from Bobo, the term “Booby” was first established in England for the species of the genus “ Sula ”. This was translated into German by the ornithologist J. Th. Klein from Danzig in 1750 as "booby" and has increasingly established itself as the name for the family of these oarsopods .
Even before they settled on Heligoland as a breeding bird, gannets were regularly observed in the waters around this island and on the coasts of Lower Saxony and Schleswig-Holstein . Accordingly, there are a number of popular German names. These include the names Tölpel von Bassan, Bassaner Tölpel or Bassaner Pelikan, based on the well-known Bass Rock colony. The large, white-feathered bird was very often referred to as the goose and was then appropriately named Bassaner goose, Scottish goose or Soland goose. The term “northern gannet”, which is common in English, also contains the stem gan, which is also found in gander or goose. Because of their harsh calls, gannets were sometimes referred to as sea ravens.
Appearance
Body size and plumage
Northern gannets are the largest and heaviest of the gannets. Breeding birds weigh between 3 and 3.4 kilograms. The bird is about 81-110 centimeters tall and the wingspan is between 165 and 180 centimeters. The beak is measured from the forehead fletching between 9 and 11 centimeters long. A size difference between the sexes cannot be determined.
Adult northern gannets have a predominantly pure white body plumage. There is no sexual dimorphism in the plumage. The plumage is water-repellent, which allows northern gannets to swim at sea for long periods of time. They grease it with the waxy secretion of the oil glands by either spreading the secretion with their beak in the plumage or rubbing their head first on the oil gland and then on the rest of the plumage. The wings of the hand and the coverts of the long, narrow wings are feathery brown to black. The head, the nape and the sides of the neck differ from the rest of the body plumage by a light yellow to deep yellow color, depending on the individual and the season. In some individuals this yellow coloration can be completely absent. The reins and chin are not feathered on the head. The visible skin is black in color and gives the gannets a distinctive facial expression.
Since the tips of the feathers are white, young birds that are just flinging appear spotted with white. The white dots on the head and back are particularly dense. They have a V-shaped white spot at the end of their backs. The plumage of one-year-old young birds, on the other hand, can be almost completely brown. Since the birds go through two to three moulting cycles at the same time in the second year of life , the color of the plumage varies greatly in older young birds. Young birds can already show the white plumage and the yellowish head color of adult birds on the front of their bodies, while they still have a predominantly brown plumage on the back. They only show the plumage of adult birds from the age of five.
The newly hatched chicks are initially naked and have blue-black to black skin. By the second or third day, their eyes are even completely or partially closed. By the second week of life they have grown a white downy dress, which gives them a woolly appearance. This downy dress gradually gives way to dark brown and white-spotted plumage as early as the fifth week of life.
Other features of the appearance
The beak of the gannet is long, strong and conical in shape. It ends in a tip that is slightly curved downwards. In the front half it has sharp cutting edges. In fully grown gannets, the beak is blue-gray in color and has dark gray to black beak grooves. In newly hatched chicks the beak is gray and in not yet sexually mature young birds it is brown in color.
The eyes are large and directed forward. The iris is light blue to light gray and surrounded on the outside by a black thin ring. The four toes are like all species of the order Suliformes entirely with webbed connected. The color of the webbed gannets is black-brown to black-gray. The noticeable yellow-green lines that run along the toes and continue on the legs likely play a role in mating behavior. The back toe is turned inward and set deep. This anatomical adaptation, which can be found in all types of gannet, allows the gannets to have a good grip on steep cliffs.
Anatomical peculiarities
Northern gannets are shock divers who dive into the water at speeds of up to 100 km / h. They have some adaptations in their physique that support this diving performance. Northern gannets, for example, lack external nostrils. But they have secondary nostrils that can be closed by movable flaps when diving. The ear opening is very small, covered by feathers, and can be closed even further by muscles. The sternum of the northern gannet is strong and so long that it lies like a shield over the bowels and is able to protect the bowels from the force of the impact on the water.
The air sacs , which are more developed in the northern gannet than in other bird species, presumably also have the function of protecting the body during shock diving. Subcutaneous air sacs are found on the underside and sides of the body. Inner air sacs lie between the chest muscles and the sternum and at the end of the chest muscles and the ribs. The air sacs are connected to the lungs by ducts and fill with air when you breathe in. Muscle contractions, on the other hand, force the air out of the air sacs.
As the gannet breeding furthest north, the northern gannet has to protect itself from hypothermia. Northern gannets therefore have a subcutaneous layer of fat, thick down plumage and tightly overlapping plumage. The northern gannet can reduce the loss of body heat through the webbed feet by only having a strong blood supply during the nesting period.
Flight image, swimming behavior and gait
Northern gannets have long and narrow wings that start far behind the body. As a result, northern gannets are excellent glider pilots who can make efficient use of air currents. In calm, windless weather, their flight speed is around 55 to 65 km / h. Your flight muscles are relatively poorly developed. Most bird species have a share of flight muscles in the total weight of around 20 percent. In the case of gannets, however, the proportion is only 13 percent. The pectoralis minor , with which birds lift their wings when flying, is particularly small in gannets. This contributes to the fact that northern gannets always need a run-up distance in order to be able to take off. Since gannets are also bad runners, they are unable to start from flat land. They also start running from the water. To do this, they turn against the wind and fly up with heavy flaps of their wings. In windless weather but relatively high waves, gannets are occasionally unable to take off. It can then happen that they wash ashore. Similar to albatrosses , northern gannets take advantage of the updrafts created at the front of the waves while in flight. Northern gannets can only be seen over the mainland if they have been drifted there by storms.
Northern gannets usually land in the water with a shallow dive. Landing maneuvers in which northern gannets land on the water with their feet stretched forward, similar to pelicans or cormorants , rarely occur with the northern gannet. They lie very high on the water. The tail usually protrudes semi-diagonally upwards. Landing on land looks cumbersome and can end in falls, as the narrow wings do not allow agile maneuvers in the air. As a maneuvering aid, northern gannets use both their tail and their feet. Foot and running injuries are relatively common in landings that are not supported by wind. In the boobies of the genus Morus, broken or pulled wings are even a major cause of death in adult birds after landing accidents. Since the legs are set far back on the body, the northern gannet has a waddling, duck-like gait on land. The wings are raised a little while walking.
voice
Northern gannets do not have a pronounced repertoire of calls. The typical call is a "rab-rab-rab", which can be heard both at the nest and when the boobies dive for fish in groups. A soft, drawn-out "oo-ah" can be heard from gannets taking off for flight. The call to returning birds to the breeding colony sounds more like "arrah-arrah". These calls can be heard about twice per second from landing birds. Due to the large number of returning birds, this loud call can be heard continuously in a breeding colony. There is no gender difference in call behavior or voice repertoire with gannets.
The ornithologist Bryan Nelson has come on the basis of his investigations to the conclusion that it is for the breed in colonies booby species typical to not only recognize their respective partners and their respective offspring by his voice, but that they are also able to Identify brooding boobies in the neighborhood. "Foreign" boobies are attacked much more aggressively.
distribution
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The breeding grounds of the northern gannet are mainly found on the coasts that are influenced by the Gulf Stream. Exceptions to this are the Canadian breeding grounds in the Gulf of St. Lawrence and those on the east coast of Iceland. The waters that can be reached from the breeding rocks have a surface temperature of around 10 to 15 ° C in summer. The relationship between the surface temperature of the water and the breeding areas is only an indirect one. The water temperature determines the distribution of the herring as well as the mackerel and other important food fish of the northern gannet. The distribution of the breeding grounds of the northern gannet is in turn closely related to these food fish. Northern gannets are absent from some of the waters where these food fish are found. Again, however, there are no suitable breeding rocks here.
Among all gannets, the northern gannet is the species that breeds most northerly and resides in regions that can be very stormy and cold. Most booby species live near the equator. The Australian gannet , which belongs to the same genus as the northern gannet , breeds closest to the Antarctic. Its distribution area - the south and east coast of Australia to New Zealand - is by far not exposed to as cold and stormy weather. According to ornithologist Bryan Nelson , it is the combination of body weight, beak strength and the ability to dive very deeply and obtain food far away from the nesting rocks that allowed the northern gannet to develop this habitat. Its ability to build up fat reserves allows it to get along without food for longer periods and thus, for example, to withstand longer periods of bad weather better. Thanks to its physical strength and beak strength, it can successfully hunt even strong and muscular fish like mackerel.
The northern range limit of the northern gannet is determined by whether the waters remain ice-free during the long breeding season. The islands on the coast of Greenland and Svalbard offer both sufficient food and breeding opportunities. However, the arctic summer is too short for the gannet breeding season, which is between 26 and 30 weeks. For the southern limit of distribution, the distribution of the most important food fish is decisive.
Well-known breeding colonies of the northern gannet
Some of the colonies where gannets breed have been in use for at least several hundred years. The conspicuous breeding rocks - due to the even distance between the nests, rock islands populated by gannets appear as if they were covered with snow - were partly mentioned in writing very early on. The oldest written evidence of a colony is that for the island of Lundy from 1274. Even then, people complained that the population had fallen sharply due to the gathering of eggs and the hunt for the boobies. The colony became completely extinct in 1909. Among the best known large colonies are
- Bass Rock on the Scottish east coast , for which the first written evidence dates from 1448. In 2004 there were more than 48,000 nests there.
- the Hebridean islands of St. Kilda and Sula Sgeir . St. Kilda is currently the largest European breeding colony with around 60,000 nests.
- the Welsh island of Grassholm in the Pembrokeshire Coast National Park , owned by the Royal Society for the Protection of Birds ; around 39,000 pairs of birds breed here (the third largest European colony).
- the largest colony in Iceland is on Eldey Island . About 14,000–15,000 breeding pairs breed here. The island has thus reached its maximum capacity: There is no longer any space to create new nests. Non-breeding northern gannets, which can usually be seen on the edge of every colony, are also missing here. The reason for this is obviously also a lack of space.
- about 27,000 pairs breed on the rocky island of Little Skellig in West Ireland .
European breeding colonies can also be found on the south-west Irish coast, the central Norwegian west coast with the island Runde , in the north of Norway Syltefjord , Hovflesa and Storstappen . At 71 ° 08'N, Storstappen is the northernmost breeding colony. The southernmost is on the coast of Newfoundland at 46 ° 50'N. The southernmost European breeding colony is that on the Île Rouzic in the Sept Îles archipelago in France . The only breeding site in Germany is Helgoland , where gannets have only been breeding since 1991. The colony had 93 breeding pairs in 2000 and 145 breeding pairs three years later. Northern gannets have also been breeding in the Barents Sea since 1996 . In North America, the breeding grounds are on the coast of Newfoundland and on islands in the Gulf of Saint Lawrence . The largest colony comprises 32,000 nests and is located on the island of Bonaventure near Percé .
Duration
In 2004, 45 gannet breeding colonies were known worldwide and the number of nests created and occupied annually was estimated at 361,000. The birds that breed on the Scottish coast make up about 60 percent of the world's population. A few colonies are declining, overall the gannet population seems to be increasing by three to five percent annually. The causes are, first of all, the almost complete cessation of hunting of the gannet for its meat or feathers. This ended around the turn of the 20th century. It is estimated that in 1939 the number of colonies worldwide was 22 and around 83,000 nests were incubated. That would mean that since then the number of colonies has more than doubled and the number of individuals has more than quadrupled. The observations on individual breeding rocks confirm rapid increases. The colony on the North American island of Bonaventure increased by 34 percent between 1984 and 1994. The fact that the boobies profited from the increasing deep-sea fishing is said to have contributed to the increase in the population over the last few decades.
The total population is given by the IUCN as around 530,000 animals. The stocks are increasing. This means that the species is considered "not endangered".
Food and subsistence
The food reasons
The northern gannet hunts for fish during the day, especially as a shock diver. At certain times of the year it can also find its prey near the coast. Among all the birds of the order of the Suliformes, however, the northern gannet, together with the gray-footed booby, is the one that covers the greatest distances in search of fish. Evidence shows that breeding northern gannets look up to 320 kilometers from the breeding colony. About two percent of the breeding birds of the Bass Rock on Scotland's east coast look for food on the Dogger Bank, for example . This is between 280 and 320 kilometers from the Scottish breeding rock. It is likely that the maximum distance that northern gannets are willing to travel in search of food is twice that. As a rule, the feeding grounds sought are less than 150 kilometers from the breeding colony.
The shock diving
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Northern gannets can spot their prey from heights of up to 45 meters. The normal altitude from which they peek for fish is ten to twenty meters. If a northern gannet has discovered prey fish during its search flight, it goes into a dive by tilting one of its wings forward at an angle. He can adjust the direction of his dive by stretching his legs and spreading the webbed feet as well as flapping the wings, in which the control springs are folded up or down. Immediately before diving into the water, the wings, which can be stretched out or only slightly bent during the dive, are placed close to the body. The head and neck are protruding. The beak is closed. When it hits the surface of the water, it has a speed of around 100 km / h. Northern gannets usually stay submerged for five to seven seconds. A few birds take 20 seconds to get out of the water. Very often they rise straight back into the air and dive back into the water from a height of three to four meters.
Northern gannets usually submerge targeted prey and grab it on the way up. Normally sized fish are generally swallowed from the head. Small fish are also swallowed across or from behind. Swallowing movements can occasionally be seen in emerging birds.
Because of its white plumage color, a gannet diving is very noticeable to its conspecifics and is interpreted to mean that an individual has discovered a school of fish. One often sees gannets diving for fish in groups. The collective hunt increases the catch rate of the individual bird. The gannets, which pounce independently of each other, confuse the prey fish, making it difficult for them to avoid the blows.
In the French language, this behavior earned him the name “Le Fou de Bassan” - the “crazy” bird from the basin islands: the fishermen who watched him could not at first explain why he plunged into the water and always with an empty one Schnabel reappeared. The ascent is made easier for the birds by the subcutaneous and internal air sacs. You can get back to the surface very quickly without great effort.
As an alternative catching method to shock diving, the northern gannet dives for fish directly from the surface of the water. To search for fish, he swims on the water and dips his head to look for them.
The range of prey
In addition to herring and mackerel , among others, the following types of prey spectrum of the gannet: sardine , anchovy , shad , smelt , garfish , cod , haddock , coalfish , Pollack , pouting , poor cod , whiting , Norway pout and horse mackerel , mullet , sea bream , mullet and sand eel . All species are schooling fish. Of the fish species such as cod, haddock, coalfish and hake, in which the adult fish become very large, only the young are eaten.
Similar to the great gulls , the kittiwakes , the kittiwakes and the fulmars , northern gannets use the food that is available to them through deep-sea fishing. They circle near fishing ships and quickly learn to associate the sound of the wind with which the net is being hauled in with food when the ships are idle. There they also take fish as food, which is not normally part of their prey range, and they also eat fishing waste that is thrown into the sea.
Reproduction
Return to the colony
Experienced breeding pairs are usually the first gannets to return to their breeding colonies. The time of return varies depending on the location of the colony. The northern gannets that breed on Bass Rock usually return to the island in the penultimate week of January in large flocks of up to 1000 individuals. The Icelandic breeding sites, on the other hand, are not settled until the end of March to April. The non-breeding northern gannets usually follow the breeding birds at intervals of several weeks. Northern gannets usually do not return to a breeding colony until they are two to three years old. This does not necessarily have to be the breeding colony from which they themselves originate. Apparently many gannets settle in foreign breeding colonies. However, no case is known to date where a northern gannet successfully brooded in one colony and gave up that colony in favor of another.
Northern gannets returning for the first time are not yet able to reproduce, but rather stay on the edge of the colony - provided there is enough space in the nesting rock. Four to five-year-old northern gannets are already building nests, but they have no young or eggs. Males of this age also fly over the colony in search of empty nests and also occupy them. However, they will only aggressively defend these nesting sites once they have owned them for at least two to three days. A nest that is currently unoccupied because its “owner” is fishing will be cleared by the “occupier” without an aggressive fight as soon as the adult bird has returned.
Nest building
The nest is preferably placed on slopes and ledges of the cliffs. Only where these places are occupied, gannets also move to island tops or flat areas of their nesting rocks. While it is easy for northern gannets to rise into the air from nests on the ledges, they have difficulty starting from the flatter spots. It is usually not possible to take off from there without getting close to the nests of their conspecifics. Since northern gannets react very aggressively when a conspecific comes near the nest, these locations are associated with significantly more stress for the birds. Basically, however, the nests are built close to conspecifics. Places that are favorable for creating nests remain unused if they are too far away from the breeding colony. On average there are 2.3 nests per square meter.
The nests consist of seaweed, grass, earth and flotsam of all kinds. The nesting material is mainly collected by the male. The nests are rebuilt every year, as the weather during the winter season destroys the nests of the previous year, with the nest being built over the entire breeding period. Among other things, the edge height of the nest increases, as gannets settle the breeding season through excrement on the edge of the nest. The nests are on average about 30 centimeters high and 50 to 75 centimeters in diameter. At preferred nesting sites, the distance between the individual nests is so large that the beaks of the northern gannet cannot reach each other when the neck is stretched out.
Aggression behavior at the nesting site
In northern gannets, occupying and aggressively defending a nesting site within a colony appears to be the trigger and the basis for a range of mating-related behaviors.
Fighting only occurs between members of the sexes. The behavioral repertoire of the females - they turn their heads away from aggressive males and present the back of the neck towards them - leads to them being grabbed by the neck and dragged away by males defending their breeding site. Conversely, if a foreign male intrudes into the immediate vicinity of a nest occupied by a female, the female does not react. Foreign females, on the other hand, are attacked very violently. The fights are particularly fierce when a male is involved who occupies a breeding site for the first time. Northern gannets can suffer very severe injuries. Each fight is preceded by a threat. Threatening behavior can be observed throughout the year during the breeding season. It is directed against the neighboring pairs. So-called "bows" on the part of the male are also often seen. They signal to the neighbors which male is occupying a nest. With these bows, which always last four to five seconds, the beak is directed downwards, the wings are slightly raised. The head is shaken slowly and then faster.
Pair formation
Male gannets that have occupied a breeding site have to woo for females. Unmated females are usually between four and five years old. Before they settle at a point in the colony, they fly over the colony several times. If they land, their posture, which includes a strongly elongated neck, identifies them as unmated. This posture is sufficient to trigger advertising in unpaired males.
The male's advertising is similar to the bowing gesture with which a male signals possession of a nest. The wings remain closed, the head is shaken a little harder. When the female approaches, the male sometimes engages in an aggressive act. The female's “looking away” - a ritualized averting of the beak, in which the back of the neck is presented to the attacking male - ends or soothes the male's aggressiveness. At this point the female is still ready to mate with multiple males. Sometimes the female mates with five different partners in a period of two hours. As the bond with a certain male increases, the welcoming ceremony that is characteristic of northern gannets takes place between the two birds. The two birds stand upright chest to chest, their necks are pointing upwards and fencing movements are made with their beaks. The two birds let out loud calls.
Egg and young bird
Northern gannets only lay a single egg at a time, which is oval in shape and weighs an average of 104.5 grams. The egg corresponds to about 3.3 percent of the body weight of the female. Compared to other sea birds , this is very light. If there are two eggs in a nest, it was either laid by a second female or the egg was stolen from one of the neighboring nests. Northern gannets lay again when their egg is lost. The egg is incubated by the parent birds for between 42 and 46 days. Boobies lack the brood spot . They incubate the egg with the well-perfused webs by embracing it on both sides.
The hatching process of the young bird can take up to 36 hours. At this point the egg is on the webbed feet. So far, it has not been conclusively clarified what the trigger is that boobies transport their eggs onto their webbed eggs shortly before they hatch. This is probably due to the chick's voice feeling sounds. However, an egg picked by the hatching chick would break under the webbed feet under the weight of the breeding parent bird. In fact, large numbers of young birds die in this way in first-time breeding pairs. The young bird is also fluttered on the tips of the webbed feet . The parent birds only leave the young bird alone in exceptional cases. An unguarded chick is often killed by other colony residents. A chick is also exposed to the aggression of the male parent bird.
The feed transfer between the adult and young bird takes place by the young bird pushing its head into the throat of the adult bird. The young birds master this at the earliest from their 15th day of life. Until then, the adult bird takes the boy's head in its beak and chokes up semi-liquid food. Older young birds are fed with fished fish. Two adaptations help ensure that the young birds do not fall from the cliffs into the sea: They have a strong tendency to stay in the nest until they fly out and they do not move their wings when begging. The latter prevents them from being carried out of the nest on the narrow rock ledges.
The parent birds can feed the young bird for up to 11 or 12 weeks. Feeding is not stopped by the parent birds, rather the young bird decides to give up its close bond with the nest: around their 75th day of life, the young boobies sail from the nesting rock to the sea surface. According to the current state of knowledge, this jump ends any connection to the parent birds. The young birds have not yet fledged at the time. However, their average weight is around 4 kilograms. This means they have enough fat reserves to go without food for two to three weeks. Their high weight and their as yet untrained ability to fly do not allow them to do more than float down from the ledges onto the sea. In unfavorable wind conditions it often happens that the young birds are blown against the cliffs and have a fatal accident there.
Young birds that grow up in nests on the island crest are violently attacked by the other adult birds as they run to the edge of the breeding rock. The young birds that are not yet able to fly then drift on the sea for a period of two to three weeks. During this time they have to learn both to fish and to fly. If longer periods of bad weather occur during this time, a large number of the young birds die.
Migration of the juveniles and the parent birds
Fledglings migrate considerable distances south from their breeding colony. Migrations almost to the equator are documented. For example, one of the young birds of the Bass Rock colony was rediscovered in its first year of life 4,800 kilometers further south at 16 ° N 24 ° W. Some of the young birds return to their breeding colony in their second year of life. They arrive there later than the breeding birds and leave at the end of the breeding season to migrate south again. On their second migration, however, they cover less long hikes.
Adult northern gannets migrate less purposefully after the breeding season and stay between 800 and 1,600 kilometers from their breeding colony. So far, no colony-specific wintering sites have been identified. Many of the adult birds can be found in the western Mediterranean . Since they are reluctant to fly over land, they reach the Mediterranean via the Strait of Gibraltar . Some of the northern gannets follow the African coast further south and reach the Gulf of Guinea . There, the area in which the northern gannet resides overlaps that of the Cape gannet .
With the Canadian gannets, the young birds migrate to the Gulf of Mexico. On their return flight from March they cover up to 90 kilometers a day. Adult birds don't migrate quite as far.
The northern gannet defends the territory around its nest very aggressively. He fights fierce beaked fights with intruders. He keeps a distance from his fellow species that is roughly twice his range. Despite this distance, the colonies look so densely populated from the air that they are reminiscent of snow-covered slopes.
Northern gannets live in monogamy; Although they separate outside of the brood care period and move away independently of their colonies, they meet again as a pair in the following breeding season. If one of the partners has died, the remaining bird leaves the breeding site: Together with the other lone animals, it moves to another part of the colony to find a new partner.
Life expectancy
A very high percentage of the northern gannet cubs that hatch also fledge. Hans Heinrich Reinsch gives the proportion at 89 to 94 percent. For many animal species that only raise one or two young, the rate is only 50 percent. However, only 30 percent of fledgling birds reach the point in their life when they are able to reproduce. Life expectancy is around 16 years, but the oldest ringbirds found were older than 24 years.
Plastic litter floating in the ocean is one of the risks that both adult and juvenile birds are exposed to . Such waste is found in around 50 percent of the nests, for example northern gannets use fishing nets that are floating in the sea to equip the nest. Northern gannets can get tangled in them and thus have a fatal accident.
Systematics
The northern gannet probably evolved from ancestors of the Cape gannet who migrated north and adapted there to the colder and stormier environmental conditions. Northern gannets in particular became heavier and larger and probably for this reason began to develop on breeding grounds on cliffs.
Human and northern gannet
The sometimes very intensive hunting resulted in a number of colonies becoming extinct towards the end of the 19th century and the beginning of the 20th century. In addition to the island of Lundy, this includes several colonies in the Gulf of St. Lawrence. The hunt was so intense because the meat of the caught animals was used not only as human food, but also as bait for fishing for cod . The northern gannet is not aggressive or dangerous towards humans. Injured and disoriented animals or abandoned young animals that are found by humans try to defend themselves, however. There is a risk of eye injuries from the animal's beak if you try to touch it.
In recent years, more and more plastic waste has been used to build nests. Plastic waste was found in up to 97% of the nests. Young and adult birds can get entangled in the garbage and perish. Seven young birds and five adult birds died as entanglement victims on Heligoland in 2014.
literature
- Hans-Günther Bauer, Einhard Bezzel and Wolfgang Fiedler (eds.): The compendium of birds in Central Europe: Everything about biology, endangerment and protection. Volume 1: Nonpasseriformes - non-sparrow birds. Aula-Verlag Wiebelsheim, Wiesbaden 2005, ISBN 3-89104-647-2 .
- Josep del Hoyo et al .: Handbook of the Birds of the World. Volume 1: Ostrich to Ducks. Lynx Edicions, 1992, ISBN 84-87334-10-5 .
- Bryan Nelson : The Atlantic Gannet. Fenix Books LTd, Norfolk 2002, ISBN 0-9541191-0-X .
- Bryan Nelson: Pelicans, Cormorants and their relatives. Oxford University Press, 2005, ISBN 0-19-857727-3 .
- Hans Heinrich Reinsch: The gannet , Ziemsen Verlag, 1969.
Web links
- Morus bassanus in the endangered Red List species the IUCN 2008. Posted by: BirdLife International, 2008. Accessed on December 18 of 2008.
- Videos, photos and sound recordings for Sula bassana in the Internet Bird Collection
- Web camera of the colony on Eldey
- Video: Sula bassana (Sulidae) - flight maneuvers . Institute for Scientific Film (IWF) 1980, made available by the Technical Information Library (TIB), doi : 10.3203 / IWF / E-2520 .
- Feathers of the northern gannet
Individual evidence
- ↑ a b Reinsch, 1969, p. 33.
- ↑ Reinsch, 1969, p. 7, Nelson, 2002, pp. XV - XVII and Nelson, 2005, p. 308.
- ↑ For a detailed description of all relevant dimensions, see Reinsch, 1969 p. 15 and Nelson, 2005, p. 587.
- ↑ a b Nelson, 2005, p. 133.
- ↑ a b Reinsch, 1969, p. 13.
- ↑ Nelson, 2002, p. 9.
- ↑ Reinsch, p. 14f.
- ↑ Reinsch, 1969, p. 61.
- ↑ Reinsch, p. 9.
- ↑ Reinsch, p. 16.
- ↑ Reinsch, 1969, p. 16.
- ↑ The Australian gannet is the species that breeds furthest in the south. Compared to the northern gannet, this gannet breeds in climatically more favorable regions.
- ↑ Nelson, 2005, p. 134.
- ↑ Nelson, 2002, p. 27.
- ↑ Nelson, 2005, p. 130.
- ↑ Nelson, 2002, p. 27.
- ^ Nelsons, 2002, p. 27.
- ↑ Reinsch, p. 63.
- ↑ Nelson, 2005, p. 158. Nelson also points out, however, that this statement is based primarily on studies of a colony.
- ↑ Nelson, 2005, p. 129.
- ↑ Nelson, 2002, pp. 27f. To give his readers a feel for the atmosphere of a breeding colony, Nelson compares the feeling of standing in the middle of a breeding colony as large as Bass Rock to the feeling of being part of an excited crowd in a football stadium.
- ↑ Nelson, 2005, pp. 129f and 310
- ↑ a b c Reinsch, 1969, pp. 35-49.
- ↑ Nelson, 2002, p. 24
- ↑ a b Nelson, 2005, p. 315.
- ↑ Nelson, 2005, p. 138
- ↑ Reinsch, p. 33 and p. 99f.
- ↑ a b c d Nelson, 2005, p. 311.
- ↑ Reinsch, 1969, p. 31.
- ↑ a b Bauer et al., P. 232.
- ↑ a b Nelson, 2005, p. 312.
- ↑ Nelson, 2002, p. 33
- ↑ a b Nelson, 2005, p. 320.
- ↑ Reinsch, 1969, p. 54.
- ↑ a b Reinsch, 1969, p. 53.
- ↑ Nelson, 2005, p. 321.
- ↑ Nelson, 2005, p. 141.
- ↑ Reinsch, p. 50
- ↑ Reinsch, 1969, p. 51.
- ↑ Reinsch, 1969, p. 56 f.
- ↑ Nelson, 2002, XIII.
- ↑ Nelson, 2002, p. 37.
- ↑ Reinsch, 1969, p. 56
- ↑ Reinsch, 1969, p. 75.
- ↑ Reinsch, 1969, p. 74.
- ↑ Nelson, 2005, p. 328.
- ↑ Nelson, 2005, p. 326.
- ↑ Reinsch, 1969, p. 77
- ↑ Reinsch, 1969, p. 79.
- ↑ Reinsch, 1969, p. 80.
- ↑ Reinsch, 1969, p. 59.
- ↑ Nelson, 2005, p. 150.
- ↑ Nelson, 2005, pp. 153 and 332.
- ↑ Nelson, 2005, p. 334.
- ↑ Reinsch, 1969, p. 62.
- ↑ Reinsch, 1969, p. 73.
- ↑ Nelson, 2002, p. XIII.
- ↑ Nelson, 2005, pp. 334 f.
- ↑ Reinsch, 1969, pp. 88f.
- ↑ Nelson, 2005, p. 316 f.
- ↑ Nelson, 2005, p. 329.
- ↑ Bezzel, Einhard, Compendium of the birds of Central Europe, Aula Verlag, Wiesbaden
- ↑ Nelson, 2005, p. 217.
- ↑ Nelson, 2005, p. 314.
- ↑ Reinsch, 1969, p. 99.
- ↑ Sebastian Conradt: The curse of cheap plastic . Seevögel Volume 37, 2016, pp. 4–13
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