Post by Vodmeister on Jun 3, 2013 2:18:54 GMT 5
The brown bear (Ursus arctos) is a large bear distributed across much of northern Eurasia and North America. It can weigh from 170 to 770 kilograms (350 to 1700 lbs) and its largest subspecies, the Kodiak Bear, is second only to the polar bear as the largest member of the bear family and as the largest land-based predator.
There are several recognized subspecies within the brown bear species. In North America, two types are generally recognized, the coastal brown bear and the inland grizzly, and the two types could broadly define all brown bear subspecies. Grizzlies weigh as little as 350 lb (159 kg) in Yukon, while a brown bear, living on a steady, nutritious diet of spawning salmon, from Coastal Alaska and Russia can weigh 1500 lb (682 kg). The exact number of overall brown subspecies remains in debate.
While the brown bear's range has shrunk, and it has faced local extinctions, it remains listed as a least concern species by the IUCN, with a total population of approximately 200,000. Its principal range countries are Russia, the United States (mostly in Alaska), Canada, the Carpathian region (especially Romania), and Finland where it is the national animal. The brown bear is the most widely distributed of all bears.
Brown bears are thought to have evolved from Ursus etruscus. The oldest fossils occur in China from about 0.5 million years ago. They entered Europe about 250,000 years ago, and North Africa shortly after. Brown bear remains from the Pleistocene period are common in the British Isles, where it is thought they outcompeted cave bears. The species entered Alaska 100,000 years ago, though they did not move south until 13,000 years ago. It is thought that brown bears were unable to migrate south until the extinction of the much larger Arctodus simus. Several paleontologists suggest the possibility of two separate brown bear migrations: grizzlies are thought to stem from narrow-skulled bears which migrated from northern Siberia to central Alaska and the rest of the continent, while Kodiak bears descend from broad-skulled bears from Kamchatka which colonised the Alaskan peninsula. Brown bear fossils discovered in Ontario, Ohio, Kentucky and Labrador show that the species occurred farther east than indicated in historic records. Brown bears are massively built and heavy bodied animals. They have a large hump-like mass of muscle on their shoulders, which coupled with their long claws, provide brown bears with a great digging ability. Brown bears have very large and curved claws, those present on the forelimbs being longer than those on the hind limbs. They may reach 5 to 6 centimetres (2.0 to 2.4 in) and sometimes 7 to 10 centimetres (2.8 to 3.9 in) along the curve. They are never less than 6 centimetres (2.4 in) in length. They are generally dark with a light tip with some forms having completely light claws. Brown bear claws are longer and straighter than those of American black bears. The claws are blunt, while those of a black bear are sharp.
Adults have massive, heavily built concave skulls which are large in proportion to the body. The forehead is high and rises steeply. The projections of the skull are well developed when compared to those of Asian black bears: the latter have sagittal crests not exceeding more than 19–20% of the total length of the skull, while the former have sagittal crests comprising up to 40–41% of the skull's length. Skull projections are more weakly developed in female brown bears than in males. The braincase is relatively small and elongated. There is a great deal of geographical variation in the skull, and presents itself chiefly in dimensions. Grizzlies, for example, tend to have flatter profiles than European and coastal American brown bears. Skull lengths of Russian bears tend to be 31.5 to 45.5 centimetres (12.4 to 17.9 in) for males, and 27.5 to 39.7 centimetres (10.8 to 15.6 in) for females. The width of the zygomatic arches in males is 17.5 to 27.7 centimetres (6.9 to 11 in), and 14.7 to 24.7 centimetres (5.8 to 9.7 in) in females. Brown bears have very strong teeth: the incisors are relatively big and the canine teeth are large, the lower ones being strongly curved. The first three molars of the upper jaw are underdeveloped and single crowned with one root. The second upper molar is smaller than the others, and is usually absent in adults. It is usually lost at an early age, leaving no trace of the alveolus in the jaw. The first three molars of the lower jaw are very weak, and are often lost at an early age. Although they have powerful jaws, brown bear jaws are incapable of breaking large bones with the ease of spotted hyenas.
The dimensions of brown bears fluctuate very greatly according to sex, age, individual, geographic location, and season. The normal range of physical dimensions for a brown bear is a head-and-body length of 1.7 to 2.8 meters (5.6 to 9.2 ft) and a shoulder height of 90 to 150 centimeters (35–60 in). The smallest subspecies is the Eurasian Brown Bear whose mature females weigh as little as 90 kg (200 lb). Barely larger, Grizzly Bears from the Yukon region (which are a third smaller than most grizzlies) can weigh as little as 100 kg (220 lb) in the spring and the Syrian Brown Bear, with mature females weighing as little as 150 kg (330 lb). The largest subspecies are the Kodiak Bear, Siberian Brown Bear, and the bears from coastal Russia and Alaska. It is not unusual for large male Kodiak Bears to stand over 3 m (9.8 ft) while on their hind legs, and to weigh up to 680 kg (1,500 lb). The greatest weight recorded for a Brown bear in the wild is 1656 lb 751 kg for a male shot at English Bay, Kodiak Island.
There are about 200,000 brown bears in the world. The largest populations are in Russia with 120,000, the United States with 32,500, and Canada with 21,750. 95% of the brown bear population in the United States is in Alaska, though in the lower 48 states they are repopulating slowly but steadily along the Rockies and the Western Great plains. Although many people hold on to the belief that some brown bears may be present in Mexico and the Atlas Mountains of Morocco, both are almost certainly extinct. The last Mexican brown bear was shot in 1960. In Europe, there are 14,000 brown bears in ten fragmented populations, from Spain in the west, to Russia in the east, and from Scandinavia in the north to Romania(4000–5000), Bulgaria (900–1200), Slovakia (with about 600–800 animals), and Greece (with about 200 animals) in the south. They are extinct in the British Isles, extremely threatened in France and Spain, and in trouble over most of Central Europe. The Carpathian brown bear population of Romania is the largest in Europe outside Russia, estimated at 4,500 to 5,000 bears. Scandinavia is home to a large bear population, with an estimated 2,500 (range 2,350–2,900) in Sweden, 900–1300 in Finland, and 70 in Norway. Another large and relatively stable population of brown bears in Europe, consisting of 2,500–3,000 individuals, is the Dinaric-Pindos (Balkans) population, with contiguous distribution in north-east Italy, Slovenia, Croatia, Bosnia and Herzegovina, Serbia, Montenegro, Macedonia, Albania, Bulgaria and Greece.
Brown bears were once native to Asia, the Atlas Mountains in Africa, Europe, and North America, but are now extinct in some areas and their populations have greatly decreased in other areas. They prefer semi-open country, usually in mountainous areas.
Brown bears live in Alaska, east through the Yukon and Northwest Territories, south through British Columbia and through the western half of Alberta. Small populations exist in the Greater Yellowstone Ecosystem of northwest Wyoming (with about 600 animals), the Northern Continental Divide Ecosystem of northwest Montana (with about 750 animals), the Cabinet-Yaak Ecosystem of northwest Montana and northeast Idaho (with about 30–40 animals), the Selkirk Ecosystem of northeast Washington and northwest Idaho (with about 40–50 animals), and the North Cascades Ecosystem of north-central Washington (with about 5–10 animals). These five ecosystems combine for a total of roughly 1,470 wild grizzlies still persisting in the contiguous United States. Unfortunately, these populations are isolated from each other, inhibiting any genetic flow to occur between ecosystems. This poses one of the greatest threats to the future survival of the grizzly bear in the contiguous United States.
In Asia, brown bears are found in most of Russia, parts of the Middle East, and in a little bit of Manchuria in China. They can also be found on the island of Hokkaid? in Japan and in Western China and a little bit of Afghanistan, Pakistan, and India.
The population of brown bears in the Pyrenees mountain range between France and Spain is so low, estimated at 14 to 18 with a shortage of females, that bears, mostly female, from Slovenia were released in spring 2006 to reduce the imbalance and preserve the species' presence in the area, despite protests from French farmers.
A small population of brown bears (Ursus arctos marsicanus) still lives in central Italy (Apennine mountains, Abruzzo and Latium) with no more than 70 individuals, protected by strong laws but endangered by the human presence in the area.
In Arctic areas, the potential habitat of the brown bear is increasing. The warming of that region has allowed the species to move farther north into what was once exclusively the domain of the polar bear. In non-Arctic areas, habitat loss is blamed as the leading cause of endangerment, followed by hunting.
North American brown bears seem to prefer open landscapes, whereas in Eurasia they inhabit mostly dense forests. It is thought that the Eurasian bears which colonized America were tundra-adapted. This is indicated by brown bears in the Chukotka Peninsula on the Asian side of Bering Strait, which are the only Asian brown bears to live year-round in lowland tundra like their North American cousins.
The brown bear is primarily nocturnal. In the summer, it gains up to 180 kilograms (400 lb) of fat, on which it relies to make it through winter, when it becomes very lethargic. Although they are not full hibernators, and can be woken easily, both sexes like to den in a protected spot such as a cave, crevice, or hollow log during the winter months. Brown bears are mostly solitary, although they may gather in large numbers at major food sources and form social hierarchies based on age and size. Adult male bears are particularly aggressive and are avoided by adolescent and subadult males. Female bears with cubs rival adult males in aggression and more intolerant of other bears than single females. Young adolescent males tend to be least aggressive and have been observed making non-agonistic interactions with each other. In his Great Bear Almanac, Gary Brown lists 11 different sounds bears produce in 9 different contexts. Sounds expressing anger or aggravation include growls, roars, woofs, champs and smacks while sounds expressing nervousness or pain include woofs, grunts and bawls. Sows will bleat or hum when communicating with their cubs. The mating season is from late May to early July. Being serially monogamous, brown bears remain with the same mate from several days to a couple of weeks. Females mature sexually between the age of 5 and 7 years, while males usually mate a few years later when they are large and strong enough to successfully compete with other males for mating rights.Males however take no part in raising their cubs – parenting is left entirely to the females.
Through the process of delayed implantation, a female's fertilized egg divides and floats free in the uterus for six months. During winter dormancy, the fetus attaches to the uterine wall. The cubs are born eight weeks later, while the mother sleeps. If the mother does not gain enough weight to survive through the winter, the embryo does not implant and is reabsorbed into the body. The average litter has one to four cubs, usually two. There have been cases of bears with five cubs, although females sometimes adopt strange cubs. Older females tend to give birth to larger litters. The size of a litter also depends on factors such as geographic location and food supply. At birth, the cubs are blind, toothless, hairless, and weigh less than 450 grams (1.0 lb). They feed on their mother's milk until spring or even early summer depending on climate conditions. At this time, the cubs weigh 7 to 9 kilograms (15 to 20 lb) and have developed enough to follow her and begin to forage for solid food.
Cubs remain with their mother from two to four years, during which time they learn survival techniques, such as which foods have the highest nutritional values and where to obtain them; how to hunt, fish, and defend themselves; and where to den. The cubs learn by following and imitating their mother's actions during the period they are with her. Brown bears practice infanticide. An adult male bear may kill the cubs of another bear either to make the female sexually receptive or simply for consumption. Cubs flee up a tree when they see a strange male bear, and the mother defends them even though the male may be twice her size.
They are omnivores and feed on a variety of plant products, including berries, roots, and sprouts, fungi as well as meat products such as fish, insects, and small mammals. Despite their reputation, most brown bears are not highly carnivorous as they derive up to 90% of their dietary food energy from vegetable matter. Their jaw structure has evolved to fit their dietary habits. Their diet varies enormously throughout their differing areas based on opportunity. For example, bears in Yellowstone eat an enormous number of moths during the summer, sometimes as many as 40,000 in a day, and may derive up to half of their annual food energy from these insects. In some areas of Russia and Alaska, brown bears feed mostly on spawning salmon, whose nutrition and abundance explain the enormous size of the bears in these areas. Brown bears also occasionally prey on large mammals, such as deer, elk, moose, caribou, bighorn sheep, mountain goats, bison and muskoxen. When brown bears attack these animals, they tend to choose the young ones as they are easier to catch. When hunting, the bear pins its prey to the ground and then tears and eats it alive. On rare occasions, bears kill by hitting their prey with their powerful forearms which can break the necks and backs of large prey, such as moose. They also feed on carrion and use their size to intimidate other predators such as wolves, cougars, black bears, and occasionally tigers from their kills.
As a rule, brown bears seldom attack humans on sight, and usually avoid people. They are however unpredictable in temperament, and will attack if they are surprised or feel threatened. Sows with cubs account for the majority of injuries and fatalities in North America. Habituated or food-conditioned bears can also be dangerous, as their long-term exposure to humans causes them to lose their natural shyness, and in some cases associate humans with food. Small parties of one or two people are more often attacked than large groups, with no attacks being recorded against parties of six people or more. In contrast to injuries caused by American black bears, which are usually minor, brown bear attacks tend to result in serious injury and in some cases death. In the majority of attacks resulting in injury, brown bears precede the attack with a growl or huffing sound, and seem to confront humans as they would when fighting other bears: they rise up on their hind legs, and attempt to "disarm" their victims by biting and holding on to the lower jaw to avoid being bitten in turn. Such a bite can be as severe as that of a tiger, with some human victims having had their heads completely crushed by a bear bite. Most attacks occur in the months of July, August and September, the time when the number of outdoor recreationalists, such as hikers or hunters, is higher. People who assert their presence through noises tend to be less vulnerable, as they alert bears to their presence. In direct confrontations, people who run are statistically more likely to be attacked than those who stand their ground. Violent encounters with brown bears usually last only a few minutes, though they can be prolonged if the victims fight back.
Attacks on humans are considered extremely rare in the former Soviet Union, though exceptions exist in districts where they are not pursued by hunters. Siberian bears for example tend to be much bolder toward humans than their shyer, more persecuted European counterparts. In 2008, a platinum mining compound in the Olyotorsky district of northern Kamchatka was besieged by a group of 30 bears who killed two guards and prevented workers from leaving their homes. Ten people a year are killed by brown bears in Russia. In Scandinavia, only three fatal attacks were recorded in the 20th century.
In Japan, a large brown bear nicknamed "Kesagake" (
?, "kesa-style slasher") made history for causing the worst bear attack in Japanese history at Tomamae, Hokkaid? during December, 1915, killing 7 people (including 1 pregnant woman) and wounding 3 others (with possible another 3 previous fatalities to its credits) before being gunned down after a large-scale beast-hunt. Today, there is still a shrine at Rokusensawa (), where the event took place, in memory of the victims of the incident.
Native American tribes sympatric to brown bears often viewed them with a mixture of awe and fear. North American brown bears were so feared by the Natives that they were rarely hunted, especially alone. When Natives hunted grizzlies, the act was done with the same preparation and ceremoniality as intertribal warfare, and was never done except with a company of 4–10 warriors. The tribe members who dealt the killing blow were highly esteemed among their compatriots. Californian Indians actively avoided prime bear habitat, and would not allow their young men to hunt alone, for fear of bear attacks. During the Spanish colonial period, some tribes, instead of hunting grizzlies themselves, would seek aid from European colonists to deal with problem bears. Many authors in the American west wrote of Natives or voyagers with lacerated faces and missing noses or eyes due to attacks from grizzlies. Within Yellowstone National Park, injuries caused by grizzly attacks in developed areas averaged approximately 1 per year during the 1930s through to the 1950s, though it increased to 4 per year during the 1960s. They then decreased to 1 injury every 2 years (0.5/year) during the 1970s. Between 1980 and 2002, there have been only 2 human injuries caused by grizzly bears in a developed area. However, although grizzly attacks were rare in the backcountry before 1970, the number of attacks increased to an average of approximately 1 per year during the 1970s, 1980s, and 1990s.
There are several recognized subspecies within the brown bear species. In North America, two types are generally recognized, the coastal brown bear and the inland grizzly, and the two types could broadly define all brown bear subspecies. Grizzlies weigh as little as 350 lb (159 kg) in Yukon, while a brown bear, living on a steady, nutritious diet of spawning salmon, from Coastal Alaska and Russia can weigh 1500 lb (682 kg). The exact number of overall brown subspecies remains in debate.
While the brown bear's range has shrunk, and it has faced local extinctions, it remains listed as a least concern species by the IUCN, with a total population of approximately 200,000. Its principal range countries are Russia, the United States (mostly in Alaska), Canada, the Carpathian region (especially Romania), and Finland where it is the national animal. The brown bear is the most widely distributed of all bears.
Brown bears are thought to have evolved from Ursus etruscus. The oldest fossils occur in China from about 0.5 million years ago. They entered Europe about 250,000 years ago, and North Africa shortly after. Brown bear remains from the Pleistocene period are common in the British Isles, where it is thought they outcompeted cave bears. The species entered Alaska 100,000 years ago, though they did not move south until 13,000 years ago. It is thought that brown bears were unable to migrate south until the extinction of the much larger Arctodus simus. Several paleontologists suggest the possibility of two separate brown bear migrations: grizzlies are thought to stem from narrow-skulled bears which migrated from northern Siberia to central Alaska and the rest of the continent, while Kodiak bears descend from broad-skulled bears from Kamchatka which colonised the Alaskan peninsula. Brown bear fossils discovered in Ontario, Ohio, Kentucky and Labrador show that the species occurred farther east than indicated in historic records. Brown bears are massively built and heavy bodied animals. They have a large hump-like mass of muscle on their shoulders, which coupled with their long claws, provide brown bears with a great digging ability. Brown bears have very large and curved claws, those present on the forelimbs being longer than those on the hind limbs. They may reach 5 to 6 centimetres (2.0 to 2.4 in) and sometimes 7 to 10 centimetres (2.8 to 3.9 in) along the curve. They are never less than 6 centimetres (2.4 in) in length. They are generally dark with a light tip with some forms having completely light claws. Brown bear claws are longer and straighter than those of American black bears. The claws are blunt, while those of a black bear are sharp.
Adults have massive, heavily built concave skulls which are large in proportion to the body. The forehead is high and rises steeply. The projections of the skull are well developed when compared to those of Asian black bears: the latter have sagittal crests not exceeding more than 19–20% of the total length of the skull, while the former have sagittal crests comprising up to 40–41% of the skull's length. Skull projections are more weakly developed in female brown bears than in males. The braincase is relatively small and elongated. There is a great deal of geographical variation in the skull, and presents itself chiefly in dimensions. Grizzlies, for example, tend to have flatter profiles than European and coastal American brown bears. Skull lengths of Russian bears tend to be 31.5 to 45.5 centimetres (12.4 to 17.9 in) for males, and 27.5 to 39.7 centimetres (10.8 to 15.6 in) for females. The width of the zygomatic arches in males is 17.5 to 27.7 centimetres (6.9 to 11 in), and 14.7 to 24.7 centimetres (5.8 to 9.7 in) in females. Brown bears have very strong teeth: the incisors are relatively big and the canine teeth are large, the lower ones being strongly curved. The first three molars of the upper jaw are underdeveloped and single crowned with one root. The second upper molar is smaller than the others, and is usually absent in adults. It is usually lost at an early age, leaving no trace of the alveolus in the jaw. The first three molars of the lower jaw are very weak, and are often lost at an early age. Although they have powerful jaws, brown bear jaws are incapable of breaking large bones with the ease of spotted hyenas.
The dimensions of brown bears fluctuate very greatly according to sex, age, individual, geographic location, and season. The normal range of physical dimensions for a brown bear is a head-and-body length of 1.7 to 2.8 meters (5.6 to 9.2 ft) and a shoulder height of 90 to 150 centimeters (35–60 in). The smallest subspecies is the Eurasian Brown Bear whose mature females weigh as little as 90 kg (200 lb). Barely larger, Grizzly Bears from the Yukon region (which are a third smaller than most grizzlies) can weigh as little as 100 kg (220 lb) in the spring and the Syrian Brown Bear, with mature females weighing as little as 150 kg (330 lb). The largest subspecies are the Kodiak Bear, Siberian Brown Bear, and the bears from coastal Russia and Alaska. It is not unusual for large male Kodiak Bears to stand over 3 m (9.8 ft) while on their hind legs, and to weigh up to 680 kg (1,500 lb). The greatest weight recorded for a Brown bear in the wild is 1656 lb 751 kg for a male shot at English Bay, Kodiak Island.
There are about 200,000 brown bears in the world. The largest populations are in Russia with 120,000, the United States with 32,500, and Canada with 21,750. 95% of the brown bear population in the United States is in Alaska, though in the lower 48 states they are repopulating slowly but steadily along the Rockies and the Western Great plains. Although many people hold on to the belief that some brown bears may be present in Mexico and the Atlas Mountains of Morocco, both are almost certainly extinct. The last Mexican brown bear was shot in 1960. In Europe, there are 14,000 brown bears in ten fragmented populations, from Spain in the west, to Russia in the east, and from Scandinavia in the north to Romania(4000–5000), Bulgaria (900–1200), Slovakia (with about 600–800 animals), and Greece (with about 200 animals) in the south. They are extinct in the British Isles, extremely threatened in France and Spain, and in trouble over most of Central Europe. The Carpathian brown bear population of Romania is the largest in Europe outside Russia, estimated at 4,500 to 5,000 bears. Scandinavia is home to a large bear population, with an estimated 2,500 (range 2,350–2,900) in Sweden, 900–1300 in Finland, and 70 in Norway. Another large and relatively stable population of brown bears in Europe, consisting of 2,500–3,000 individuals, is the Dinaric-Pindos (Balkans) population, with contiguous distribution in north-east Italy, Slovenia, Croatia, Bosnia and Herzegovina, Serbia, Montenegro, Macedonia, Albania, Bulgaria and Greece.
Brown bears were once native to Asia, the Atlas Mountains in Africa, Europe, and North America, but are now extinct in some areas and their populations have greatly decreased in other areas. They prefer semi-open country, usually in mountainous areas.
Brown bears live in Alaska, east through the Yukon and Northwest Territories, south through British Columbia and through the western half of Alberta. Small populations exist in the Greater Yellowstone Ecosystem of northwest Wyoming (with about 600 animals), the Northern Continental Divide Ecosystem of northwest Montana (with about 750 animals), the Cabinet-Yaak Ecosystem of northwest Montana and northeast Idaho (with about 30–40 animals), the Selkirk Ecosystem of northeast Washington and northwest Idaho (with about 40–50 animals), and the North Cascades Ecosystem of north-central Washington (with about 5–10 animals). These five ecosystems combine for a total of roughly 1,470 wild grizzlies still persisting in the contiguous United States. Unfortunately, these populations are isolated from each other, inhibiting any genetic flow to occur between ecosystems. This poses one of the greatest threats to the future survival of the grizzly bear in the contiguous United States.
In Asia, brown bears are found in most of Russia, parts of the Middle East, and in a little bit of Manchuria in China. They can also be found on the island of Hokkaid? in Japan and in Western China and a little bit of Afghanistan, Pakistan, and India.
The population of brown bears in the Pyrenees mountain range between France and Spain is so low, estimated at 14 to 18 with a shortage of females, that bears, mostly female, from Slovenia were released in spring 2006 to reduce the imbalance and preserve the species' presence in the area, despite protests from French farmers.
A small population of brown bears (Ursus arctos marsicanus) still lives in central Italy (Apennine mountains, Abruzzo and Latium) with no more than 70 individuals, protected by strong laws but endangered by the human presence in the area.
In Arctic areas, the potential habitat of the brown bear is increasing. The warming of that region has allowed the species to move farther north into what was once exclusively the domain of the polar bear. In non-Arctic areas, habitat loss is blamed as the leading cause of endangerment, followed by hunting.
North American brown bears seem to prefer open landscapes, whereas in Eurasia they inhabit mostly dense forests. It is thought that the Eurasian bears which colonized America were tundra-adapted. This is indicated by brown bears in the Chukotka Peninsula on the Asian side of Bering Strait, which are the only Asian brown bears to live year-round in lowland tundra like their North American cousins.
The brown bear is primarily nocturnal. In the summer, it gains up to 180 kilograms (400 lb) of fat, on which it relies to make it through winter, when it becomes very lethargic. Although they are not full hibernators, and can be woken easily, both sexes like to den in a protected spot such as a cave, crevice, or hollow log during the winter months. Brown bears are mostly solitary, although they may gather in large numbers at major food sources and form social hierarchies based on age and size. Adult male bears are particularly aggressive and are avoided by adolescent and subadult males. Female bears with cubs rival adult males in aggression and more intolerant of other bears than single females. Young adolescent males tend to be least aggressive and have been observed making non-agonistic interactions with each other. In his Great Bear Almanac, Gary Brown lists 11 different sounds bears produce in 9 different contexts. Sounds expressing anger or aggravation include growls, roars, woofs, champs and smacks while sounds expressing nervousness or pain include woofs, grunts and bawls. Sows will bleat or hum when communicating with their cubs. The mating season is from late May to early July. Being serially monogamous, brown bears remain with the same mate from several days to a couple of weeks. Females mature sexually between the age of 5 and 7 years, while males usually mate a few years later when they are large and strong enough to successfully compete with other males for mating rights.Males however take no part in raising their cubs – parenting is left entirely to the females.
Through the process of delayed implantation, a female's fertilized egg divides and floats free in the uterus for six months. During winter dormancy, the fetus attaches to the uterine wall. The cubs are born eight weeks later, while the mother sleeps. If the mother does not gain enough weight to survive through the winter, the embryo does not implant and is reabsorbed into the body. The average litter has one to four cubs, usually two. There have been cases of bears with five cubs, although females sometimes adopt strange cubs. Older females tend to give birth to larger litters. The size of a litter also depends on factors such as geographic location and food supply. At birth, the cubs are blind, toothless, hairless, and weigh less than 450 grams (1.0 lb). They feed on their mother's milk until spring or even early summer depending on climate conditions. At this time, the cubs weigh 7 to 9 kilograms (15 to 20 lb) and have developed enough to follow her and begin to forage for solid food.
Cubs remain with their mother from two to four years, during which time they learn survival techniques, such as which foods have the highest nutritional values and where to obtain them; how to hunt, fish, and defend themselves; and where to den. The cubs learn by following and imitating their mother's actions during the period they are with her. Brown bears practice infanticide. An adult male bear may kill the cubs of another bear either to make the female sexually receptive or simply for consumption. Cubs flee up a tree when they see a strange male bear, and the mother defends them even though the male may be twice her size.
They are omnivores and feed on a variety of plant products, including berries, roots, and sprouts, fungi as well as meat products such as fish, insects, and small mammals. Despite their reputation, most brown bears are not highly carnivorous as they derive up to 90% of their dietary food energy from vegetable matter. Their jaw structure has evolved to fit their dietary habits. Their diet varies enormously throughout their differing areas based on opportunity. For example, bears in Yellowstone eat an enormous number of moths during the summer, sometimes as many as 40,000 in a day, and may derive up to half of their annual food energy from these insects. In some areas of Russia and Alaska, brown bears feed mostly on spawning salmon, whose nutrition and abundance explain the enormous size of the bears in these areas. Brown bears also occasionally prey on large mammals, such as deer, elk, moose, caribou, bighorn sheep, mountain goats, bison and muskoxen. When brown bears attack these animals, they tend to choose the young ones as they are easier to catch. When hunting, the bear pins its prey to the ground and then tears and eats it alive. On rare occasions, bears kill by hitting their prey with their powerful forearms which can break the necks and backs of large prey, such as moose. They also feed on carrion and use their size to intimidate other predators such as wolves, cougars, black bears, and occasionally tigers from their kills.
As a rule, brown bears seldom attack humans on sight, and usually avoid people. They are however unpredictable in temperament, and will attack if they are surprised or feel threatened. Sows with cubs account for the majority of injuries and fatalities in North America. Habituated or food-conditioned bears can also be dangerous, as their long-term exposure to humans causes them to lose their natural shyness, and in some cases associate humans with food. Small parties of one or two people are more often attacked than large groups, with no attacks being recorded against parties of six people or more. In contrast to injuries caused by American black bears, which are usually minor, brown bear attacks tend to result in serious injury and in some cases death. In the majority of attacks resulting in injury, brown bears precede the attack with a growl or huffing sound, and seem to confront humans as they would when fighting other bears: they rise up on their hind legs, and attempt to "disarm" their victims by biting and holding on to the lower jaw to avoid being bitten in turn. Such a bite can be as severe as that of a tiger, with some human victims having had their heads completely crushed by a bear bite. Most attacks occur in the months of July, August and September, the time when the number of outdoor recreationalists, such as hikers or hunters, is higher. People who assert their presence through noises tend to be less vulnerable, as they alert bears to their presence. In direct confrontations, people who run are statistically more likely to be attacked than those who stand their ground. Violent encounters with brown bears usually last only a few minutes, though they can be prolonged if the victims fight back.
Attacks on humans are considered extremely rare in the former Soviet Union, though exceptions exist in districts where they are not pursued by hunters. Siberian bears for example tend to be much bolder toward humans than their shyer, more persecuted European counterparts. In 2008, a platinum mining compound in the Olyotorsky district of northern Kamchatka was besieged by a group of 30 bears who killed two guards and prevented workers from leaving their homes. Ten people a year are killed by brown bears in Russia. In Scandinavia, only three fatal attacks were recorded in the 20th century.
In Japan, a large brown bear nicknamed "Kesagake" (
?, "kesa-style slasher") made history for causing the worst bear attack in Japanese history at Tomamae, Hokkaid? during December, 1915, killing 7 people (including 1 pregnant woman) and wounding 3 others (with possible another 3 previous fatalities to its credits) before being gunned down after a large-scale beast-hunt. Today, there is still a shrine at Rokusensawa (), where the event took place, in memory of the victims of the incident.Native American tribes sympatric to brown bears often viewed them with a mixture of awe and fear. North American brown bears were so feared by the Natives that they were rarely hunted, especially alone. When Natives hunted grizzlies, the act was done with the same preparation and ceremoniality as intertribal warfare, and was never done except with a company of 4–10 warriors. The tribe members who dealt the killing blow were highly esteemed among their compatriots. Californian Indians actively avoided prime bear habitat, and would not allow their young men to hunt alone, for fear of bear attacks. During the Spanish colonial period, some tribes, instead of hunting grizzlies themselves, would seek aid from European colonists to deal with problem bears. Many authors in the American west wrote of Natives or voyagers with lacerated faces and missing noses or eyes due to attacks from grizzlies. Within Yellowstone National Park, injuries caused by grizzly attacks in developed areas averaged approximately 1 per year during the 1930s through to the 1950s, though it increased to 4 per year during the 1960s. They then decreased to 1 injury every 2 years (0.5/year) during the 1970s. Between 1980 and 2002, there have been only 2 human injuries caused by grizzly bears in a developed area. However, although grizzly attacks were rare in the backcountry before 1970, the number of attacks increased to an average of approximately 1 per year during the 1970s, 1980s, and 1990s.
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