Polar bear ( Ursus maritimus )
|Phipps , 1774|
The polar bear ( Ursus maritimus ), also called polar bear , is a species of predator from the bear family (Ursidae). It lives in the northern polar regions and is closely related to the brown bear . In addition to Kamchatka bears and Kodiak bears , polar bears are considered to be the largest land-based predators on earth.
Features and properties
height and weight
Adult male polar bears reach a head-trunk length of 2.00 to 2.50 meters, in individual cases even up to 3.40 meters; the shoulder height is up to 1.60 meters. The weight usually varies between 420 and 500 kilograms. In females, the head-trunk length reaches 1.60 to 2.50 meters; their body weight is usually between 150 and 300 kilograms. The weight depends largely on the nutritional status of the animals: in summer, starved polar bears weigh significantly less than during the winter seal hunt. Regional differences in size also play a role. The smallest animals live on Svalbard and the largest near the Bering Strait . Like all bear species, polar bears only have a stubby tail that is 7 to 13 centimeters long.
Fur and skin
The yellowish-white fur represents a camouflage in an icy environment and consists of a dense underlayer and the outer fur hair. It is also very oily and water-repellent; Under the skin, which is black in adult animals (in babies it is still pink), there is a 5 to 10 centimeter thick layer of fat. The outer fur hair of the polar bear is hollow and transparent, not white, which in addition to the thick layer of fat provides excellent thermal insulation. In addition, the hair together with the layer of fat increase the buoyancy when swimming. The reduced heat radiation practically does not allow infrared images of the polar bear. Since the fur does not reflect ultraviolet radiation , the thesis was put forward that the outer fur hairs act as light guides and guide the radiation onto the skin. However, this thesis has been refuted, the fur itself absorbs the radiation.
Physique and gait
In terms of physique, polar bears differ from other bear species in that they have a long neck and a relatively small, flatter head. In contrast to the closely related brown bears, they lack the muscle mountain on the neck. The eyes are relatively small. The auricles are erect and round in shape. Like most bears, polar bears have 42 teeth , and like all bears, they are invertebrates . Their front legs are long and strong; the large front paws are paddle-shaped and webbed, which enables fast swimming. The polar bears can rise to maximum height on their muscular hind legs (for example when fighting or for a better panoramic view); the hind paws serve as a rudder when swimming. The soles of the feet are densely covered in hair, which protects against the cold and also prevents slipping on the ice. All four paws are armored with five non-retractable claws.
The polar bears' sense of smell is unusually well developed compared to other predators. Hearing is also quite sensitive. Polar bears explore the thickness of the ice surface by hitting the ice and listening to the water reflections in order to find optimal starting points for breaking water holes. The eyesight, on the other hand, should roughly correspond to that of humans.
Polar bears store large amounts of vitamin A in the liver. The consumption of polar bear liver can therefore lead to A-hypervitaminosis in humans , a serious health disorder that can be associated with neurological symptoms (headache, nausea, pseudotumor cerebri ) and skin damage such as angular rhinitis.
The maximum potential age of polar bears in the wild is estimated at 25 to 30 years, with very few individuals reaching the age of 20. In human care, they can live to be no more than 45 years old, although here, too, a very old age is usually just over 30 years, which is the maximum for most bears.
Distribution area and habitat
Polar bears are only found in the Arctic , and they are circumpolar , i.e. in the polar region around the North Pole . Most High Arctic polar bears spend the whole year on the coasts or on the sea ice to hunt seals . They prefer areas in which the ice remains in motion due to wind and ocean currents and is repeatedly torn open, creating ice-free areas ( polynjas ). In summer, polar bears are mostly found on the southern edges of the drift ice . With the onset of winter, they migrate south, following the vacancies. On the south coast of Hudson Bay (Canada), however, the animals are forced to return to land during the summer. After hiking for kilometers inland, they then have to be content with the little that the tundra and taiga offer them in terms of food.
For a long time, it was believed that polar bears are real hikers who follow the movement of the ice over a large area around the North Pole. However, recent observations indicate that there are greater numbers of loyal populations (19 in total). These include the polar bears of the Wapusk National Park and the Ukkusiksalik National Park .
Polar bears are usually found in several populations in the following regions of the earth (with overlaps):
- on Spitsbergen and the Franz-Josef-Land (Barents Sea population)
- in northern continental Eurasia (population areas: Kara Sea, Laptev Sea, Chukchi Sea with Wrangel Island )
- in northern Alaska and Canada , especially on the Arctic Islands, but also along the Hudson Bay and on the north coast of the Labrador Peninsula (population areas: southern Beaufort Sea, northern Beaufort Sea, Viscount-Melville Sound, McClintock Canal, Lancaster Sound , Norwegian Bay, Gulf of Boothia, western Hudson Bay, southern Hudson Bay, Foxe Basin, Davis Strait, Baffin Bay, Kane Basin)
- on Greenland (East Greenland population)
- around the North Pole (collective population of the arctic basin)
The northernmost geographical latitude at which polar bears have been observed is 88 °, the animals found furthest south can be found along Hudson Bay and the northwest coast of James Bay, which is a little further south-east . Isolated polar bears are also regularly spotted on Newfoundland and Iceland .
Way of life
Polar bears are diurnal and are mainly in motion during the first third of the day. Hiking and swimming take up about 29 percent of their time, and only 5 percent are hunting and eating. However, they spend around 66 percent of their time sleeping, resting, or lying in wait for prey. The suckling of the young takes place predominantly at lunchtime (highest sun).
The polar bears on the south coast of Hudson Bay, which live in the border area between tundra and taiga, sometimes create troughs during the summer to use the permafrost for cooling. In contrast to other bear species, polar bears do not hibernate because winter offers them optimal conditions for seal hunting. In extreme weather conditions, they can be snowed in and defy strong snowstorms and blizzards .
Only pregnant females use caves (→ reproduction ). From October or November to March, they withdraw to an earlier birth cave that they created or restored. While staying in the cave, the respiratory rate and heartbeat drop significantly. Since the body temperature nevertheless only drops slightly, this state does not represent real hibernation , but only a hibernation . The body temperature, unlike other bears, does not adapt to a reduced food supply, but should offer the young animals the greatest possible protection after birth .
Polar bears, like all bears, are loners , with the exception of mothers and their young. The hunting ground of a polar bear extends over a radius of around 150 kilometers, but the animals do not show any pronounced territorial behavior and the territories largely overlap. In places with an abundance of food, a large number of animals often hunt at a relatively short distance. Even while waiting weeks for the sea to freeze over, even adult male polar bears often show surprisingly tolerant behavior towards one another, for example in ritualized fighting games (“sparring”).
Polar bears are very good swimmers, but usually do not hunt for prey in the water. They can swim more than five kilometers an hour. They have no difficulty in dives of two minutes; the diving depth is seldom more than two meters. On land, polar bears often wander long distances for hours and cover more than six kilometers an hour. Short sprints at 30 kilometers per hour are easy for them. However, since they get very hot in the process, they are not able to maintain such speeds for long. Polar bears are inferior to reindeer or caribou in this regard .
Between late August and late October 2008, an adult female polar bear fitted with a transmitter collar swam an uninterrupted distance of 687 km in nine days. Then the female swam and walked over ice floes for a distance of 1800 km and lost a total of 22% of her weight. The same long-term study of 52 female polar bears suggests that long-distance swimming is a behavioral response to the changing ice conditions in the context of global warming.
In 2014 it was possible for the first time to extract pieces of tissue from a polar bear track in the snow and to analyze the DNA of a (female) polar bear. The WWF sees this as a cost-effective method for determining population sizes of other animal species as well.
Diet and hunting behavior
From all bear species Polar bears are dependent on meat supply at ausgeprägtesten, but like most bears are omnivorous ( omnivorous ). They are at the top of the natural arctic food chain , so they are top predators . The main component of their diet is made up of seals , mainly ringed seals , but also bearded and harp seals , collapsible caps and young or weakened walruses .
Polar bears hardly succeed in capturing seals in open water. During the winter, on the other hand, the pack ice fields at ice crevices offer the best hunting conditions. With their good sense of smell, polar bears can detect seals more than a kilometer away or under a meter thick layers of ice or snow. They usually prey on seals at their breathing holes. Camouflaged by its light fur, the polar bear is adapted to its surroundings and is difficult to perceive by the prey under the water level. The hunters often wait for hours at the ice holes until a seal comes to the surface to take a breath, and then kill the prey with lightning-fast access with teeth and paws. In another hunting method observed, they smell the often tiny air holes, under which so-called seal caves are located, from enormous distances. Here they break through the ice layer using their enormous strength and, thanks to their powerful neck, pull the prey to the surface. However, only around one in ten trapping attempts is successful.
Well-fed polar bears only eat skin and bacon from the freshly hunted prey, the rest remains. Weaker bears or arctic foxes attack what remains of the prey , but also scavenging sea birds such as seagulls . Many arctic foxes have really specialized in using leftover food from polar bears.
Exact figures for the amount of food the polar bears eat cannot be given, as they eat very irregularly and adapted to their arctic living conditions. They consume an enormous amount if they have starved for weeks or months. With their large-volume stomach, which is oversized compared to other predators, they are able to ingest very large amounts of food and then go hungry again for weeks.
Polar bears are the most fat-consuming predators. Extreme cases are known in which polar bears have eaten up to 150 kilograms above their average weight and thus had more than a year stored in their bodies. In general, polar bears switch from normal metabolism to fasting in regions where they cannot prey regularly and last for four to eight, rarely even twelve months, during which they usually only feed themselves with seaweed or seaweed to keep the digestive system active to keep.
In addition to seals and walruses, polar bears also eat small mammals such as ground squirrels , lemmings and voles , as well as birds, bird eggs and fish . Occasionally they hunt down disabled reindeer and, even more rarely, small narwhals and beluga whales . Especially in summer, when the food supply is low, polar bears eat carcasses or meat scraps and vegetable materials left behind by hunters. Due to global warming , the ice cover is decreasing. Many polar bears are therefore increasingly forced to find new food sources on land. In Greenland and Svalbard it was observed that they increasingly attacked breeding colonies of ducks and geese and the clutches were plundered.
Cannibalism is not uncommon in adult male polar bears . Young polar bears run the risk of being eaten by older male bears. Mother animals therefore avoid the males with their young or chase them away with threatening gestures.
The mating season, which lasts around a week, falls, depending on northern latitude, in the months of March to June. The time from conception to birth is around eight months. However, it is only the end of August, beginning of September to the implantation of the egg and thus to a permanent two to three months actual gestation period. This is a natural protective process; if the expectant mother is too starved due to lack of food in summer, the egg is resorbed before implantation and the pregnancy is terminated.
The birth of the bears takes place from November to January, so in winter. Pregnant females move into a birth cave about one month before giving birth, in which they hibernate ( see above ). The cave consists of a depression that is dug into the possibly peaty ground and covered with snow. This results in a one to three meter long, often steeply upwardly directed tunnel with an oval chamber that has a volume of around three cubic meters. The entrance to these birth cavities is usually designed as a cold trap . The females leave this birth cavity with their young four months later (in March or April). The areas where the females give birth to their young are called "Denning Areas" (cave areas).
The largest natal cave area in the entire Arctic is in the Canadian Wapusk National Park, which extends on the south coast of Hudson Bay around 70 kilometers southeast of the city of Churchill , between the Nelson River and Cape Churchill ("Wapusk" is the name of the Cree - Indian for "white bear"). Large Canadian cave areas also extend around the confluence of the Winisk River with Hudson Bay (southeast of Wapusk National Park), around Agu Bay on the west coast of Baffin Island near the western end of the Fury and Hecla Strait and along the to Ukkusiksalik National Park belonging to Wager Bay as well as in the northwest corner of Hudson Bay. Outside Canada, there are extensive natal cave areas in Alaska, Greenland, Svalbard and Wrangel Island in northeast Siberia.
The litter consists of one to (extremely rarely) four, but mostly two about rabbit-sized, very finely haired at birth, initially still blind and deaf boys weighing 400 to 900 grams. In the first two months they reach a weight of 10 to 15 kilograms and their white fur becomes increasingly thick. The young are suckled for 1½ to 2½ years. During this time they learn the mother's hunting behavior and are eventually abandoned by her. Under the harsh conditions of the Arctic, only about half of the young survive the first five years after birth.
Polar bears become sexually mature at around five to six years of age. From the age of 20 the fertility of females decreases significantly.
Polar bears and people
Threats and Protection
Even before coming into contact with Europeans, the indigenous peoples of North Asia and North America hunted polar bears, especially because of the polar bear fur and bacon. In the 20th century, hunting intensified due to the commercial use of all parts of the body, but mainly for pure pleasure (trophy hunting). The extensive use of airplanes to localize the animals and as a means of transport led to a drastic decline in populations in the 1950s and 1960s to a total of 5,000 to 10,000 animals worldwide. In 1973 Canada, the United States , Denmark (for Greenland ), Norway (for Svalbard) and the Soviet Union signed an agreement that would restrict hunting, protect habitats and increase joint research. Hunting by trophy hunters is still permitted in Canada, the country with the largest polar bear population, and again in Greenland since 2005, and is officially restricted by hunting quotas. Hobby hunters pay up to 30,000 euros to hunt a polar bear. Canada and Greenland signed an agreement in October 2009 that aims to limit hunting quotas to a sustainable level. There are also special regulations for indigenous peoples. An application by the USA for a strict trade ban outside the five countries with polar bear populations was rejected in March 2010 at the conference of the parties to the Washington Convention in Doha with votes from the European Union , among others .
More recently, however, two other factors have become significant for the polar bear threat. On the one hand, the increased production of oil and natural gas in the arctic regions is restricting their living space. In particular, the areas in which the females retire to hibernate and give birth are affected by this. On the other hand, it is feared that the habitats of polar bears would generally decrease drastically due to global warming . Given the predicted decline in Arctic sea ice, it is to be expected that 2/3 of the current polar bear population will be lost by the middle of the 21st century. If the sea ice disappears completely, it is unlikely that the polar bears will survive as a species. In 2015, the IUCN listed the polar bear as endangered ( vulnerable ). She estimated the population at around 26,000 animals, so the population development is unclear.
The biologists Ian Stirling and Andrew Derocher from the University of Alberta in Canada came to the conclusion in a widely acclaimed study (Stirling / Derocher 2012):
“If the climate warms up as predicted and the sea ice disappears, polar bears will largely disappear from the southern parts of their habitat by the middle of the century. It may be that they survive in the far north on the Canadian Arctic Islands and in northern Greenland for the foreseeable future; but in the long term their existence - with a greatly reduced world population in a remnant of their former settlement area - is uncertain. "
Attacks on people
In contrast to other bears, polar bears generally see humans as prey. Because of the sparse population in the Arctic and the awareness of the residents, confrontations are relatively rare, but fatal encounters are reported from time to time. The most common attacks are made by adolescents and by dams with their young. To protect against polar bears z. B. on Spitsbergen by the governor everyone outside of localities to be equipped with suitable means of defense. It is recommended to use a large-caliber rifle .
The last fatal attack by a polar bear on a person on Svalbard happened in 2011. In February 2019, there, from Greenland and Novaya Zemlya, an increased incidence of polar bears in residential areas and conflicts were reported.
Polar bears in culture
In the mythology of the Eskimos "Nanuq" ( Inuktitut - word for polar bear, English written: Nanook) generally plays an important role. Regionally there was even a myth according to which a specially highlighted polar bear was the “master of the polar bears” and could decide whether the hunters behaved according to the rules; only then is a successful polar bear hunt possible. Similar myths are also known from other arctic peoples. The polar bear adorns the coat of arms of Greenland and other coats of arms and flags of Nordic countries to this day.
The Greenland Inuit call the polar bear Angalatooq (The Great Wanderer) because of the extreme distances these animals travel in search of food. Within their traditional territories, the animals undertake extensive migrations, often thousands of kilometers per year. In the Inuit animistic tradition, the polar bear is revered as the strongest totem animal because of its intelligence, strength, fearlessness and perseverance . In East Greenland he is also called Tornassuk, the lord of the helping spirits.
Polar bears keep appearing in literature and film, especially for children. TV shows and photo books about polar bears have been popular for years. A well-known example is the picture book series Der kleine Eisbär by Hans de Beer .
Some American zoos have been celebrating February 27th as " World Polar Bear Day " since 2004 , which has since been adopted by various nature conservation and animal welfare organizations.
The polar bear on a small ice floe has been iconic for the climate crisis since 2018 .
Due to the differences in body structure, the polar bear was temporarily classified in its own genus Thalarctos . More recent systematics generally classify him in the genus Ursus , which also includes brown bears and black bears . The closest relative of the polar bear is the brown bear.
From a DNA analysis of the mitochondria in 2010 it was deduced that the species split up around 150,000 years ago. These genetic studies of mitochondrial DNA had suggested that some brown bear populations were more closely related to the polar bear than to each other. Therefore, until recently, the brown bear was considered a prime example of a " paraphyletic species" cited to challenge the traditional concept of species . Actually, one could then have viewed the polar bear as a subspecies of the brown bear.
New genetic studies have now refuted this view. A comprehensive comparison of the genetic material from the cell nucleus came to the conclusion that the splitting off of polar and brown bears occurred 338,000 to 934,000 years ago, much earlier than was estimated on the basis of analyzes of mitochondrial DNA. This study has since been confirmed by further studies, and from a phylogenetic point of view the polar bear is now considered an independent and well-differentiated species, a sibling of the brown bear. However, following the biological concept of species , brown and polar bears must be seen as subspecies of a single species.
Hybrid formation between polar and brown bears
Polar bears and brown bears can be crossed with each other and can produce fertile offspring. Hybridization between the two species has long only been known from zoo animals. On April 16, 2006, however, a hunter, Jim Martell from the US state of Idaho , shot a supposed polar bear near Sachs Harbor on Banks Island ( Northwest Territories , Canada) whose fur was not exactly white or yellowish. The bear's fur was rather a very light brown, as occurs in light grizzly bears , a subspecies of the brown bear. A DNA analysis by experts from the Ministry of Environment of the Northwest Territories revealed that the hunted animal was surprisingly a hybrid of a polar bear and a grizzly bear. Usually, both species of bears are very hostile if they ever meet in the Arctic. In addition, polar bears usually mate on the ice and grizzlies on the mainland, which is why a mating between the two species was previously considered unlikely. Climate change is now causing grizzly bears to migrate further north into territories where only the polar bear was previously found. This enables the crossing of both species as described.
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