Species of mammal
Top 10 Brown bear related articles
- 1 Evolution and taxonomy
- 2 Description
- 3 Distribution and habitat
- 4 Behavior and life history
- 5 Relationship with humans
- 6 See also
- 7 References
- 8 Bibliography
- 9 External links
|Kodiak bear on Kodiak Island|
|Brown bear range map|
The brown bear (Ursus arctos) is a large bear species found across Eurasia and North America. In North America, the populations of brown bears are called grizzly bears, while the subspecies that inhabits the Kodiak Islands of Alaska is known as the Kodiak bear. It is one of the largest living terrestrial members of the order Carnivora, rivaled in size only by its closest relative, the polar bear (Ursus maritimus), which is much less variable in size and slightly bigger on average. The brown bear's range includes parts of Russia, Central Asia, China, Canada, the United States, Hokkaido, Scandinavia, the Balkans, the Picos de Europa and the Carpathian region (especially Romania and Bulgaria), Iran, Anatolia, and the Caucasus. The brown bear is recognized as a national and state animal in several European countries.
While the brown bear's range has shrunk, and it has faced local extinctions, it remains listed as a least concern species by the International Union for Conservation of Nature (IUCN) with a total estimated population in 2017 of 110,000. As of 2012[update], this and the American black bear are the only bear species not classified as threatened by the IUCN. Populations that were hunted to extinction in the 19th and 20th centuries are the Atlas bear of North Africa and the Californian, Ungavan and Mexican populations of the grizzly bear of North America. Many of the populations in the southern parts of Eurasia are highly endangered as well. One of the smaller-bodied forms, the Himalayan brown bear, is critically endangered, occupying only 2% of its former range and threatened by uncontrolled poaching for its body parts. The Marsican brown bear of central Italy is one of several currently isolated populations of the Eurasian brown bear and is believed to have a population of just 50 to 60 bears.
Brown bear Intro articles: 21
Evolution and taxonomy
The brown bear is sometimes referred to as the bruin, from Middle English. This name originated in the fable History of Reynard the Fox translated by William Caxton from Middle Dutch bruun or bruyn, meaning brown (the color). In the mid-19th century United States, the brown bear was termed "Old Ephraim" and sometimes as "Moccasin Joe".
Generalized names and evolution
Brown bears are thought to have evolved from Ursus etruscus in Asia. The brown bear, per Kurten (1976), has been stated as "clearly derived from the Asian population of Ursus savini about 800,000 years ago; spread into Europe, to the New World." A genetic analysis indicated that the brown bear lineage diverged from the cave bear species complex approximately 1.2–1.4 million years ago, but did not clarify if U. savini persisted as a paraspecies for the brown bear before perishing. The oldest fossils positively identified as from this species occur in China from about 0.5 million years ago. Brown bears 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 might have outcompeted cave bears (Ursus spelaeus). The species entered Alaska 100,000 years ago, though they did not move south until 13,000 years ago. It is speculated that brown bears were unable to migrate south until the extinction of the much larger giant short-faced bear (Arctodus simus).
Several paleontologists suggest the possibility of two separate brown bear migrations: inland brown bears, also known as 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 colonized 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. In North America, two types of the subspecies Ursus arctos horribilis are generally recognized—the coastal brown bear and the inland grizzly bear; these two types broadly define the range of sizes of all brown bear subspecies.
There are many methods used by scientists to define bear species and subspecies, as no one method is always effective. Brown bear taxonomy and subspecies classification has been described as "formidable and confusing," with few authorities listing the same specific set of subspecies. Genetic testing is now perhaps the most important way to scientifically define brown bear relationships and names. Generally, genetic testing uses the word clade rather than species because a genetic test alone cannot define a biological species. Most genetic studies report on how closely related the bears are (or their genetic distance). There are hundreds of obsolete brown bear subspecies, each with its own name, and this can become confusing; Hall (1981) lists 86 different types, and even as many as 90 have been proposed. However, recent DNA analysis has identified as few as five main clades which contain all extant brown bears, while a 2017 phylogenetic study revealed nine clades, including one representing polar bears. As of 2005[update], 15 extant or recently extinct subspecies were recognized by the general scientific community.
As well as the exact number of overall brown bear subspecies, its precise relationship to the polar bear also remains in debate. The polar bear is a recent offshoot of the brown bear. The point at which the polar bear diverged from the brown bear is unclear, with estimations based on genetics and fossils ranging from 400,000 to 70,000 years ago, but most recent analysis has indicated that the polar bear split somewhere between 275,000 and 150,000 years ago. Under some definitions, the brown bear can be construed as the paraspecies for the polar bear.
DNA analysis shows that, apart from recent human-caused population fragmentation, brown bears in North America are generally part of a single interconnected population system, with the exception of the population (or subspecies) in the Kodiak Archipelago, which has probably been isolated since the end of the last Ice Age. These data demonstrate that U. a. gyas, U. a. horribilis, U. a. sitkensis and U. a. stikeenensis are not distinct or cohesive groups, and would more accurately be described as ecotypes. For example, brown bears in any particular region of the Alaska coast are more closely related to adjacent grizzly bears than to distant populations of brown bears, the morphological distinction seemingly driven by brown bears having access to a rich salmon food source, while grizzly bears live at higher elevation, or further from the coast, where plant material is the base of the diet. The history of the bears of the Alexander Archipelago is unusual in that these island populations carry polar bear DNA, presumably originating from a population of polar bears that was left behind at the end of the Pleistocene, but have since been connected with adjacent mainland populations through movement of males, to the point where their nuclear genomes are now more than 90% of brown bear ancestry.
Brown bears are apparently divided into five different clades, some of which coexist or co-occur in different regions.
A grizzly–polar bear hybrid (known either as a pizzly bear or a grolar bear) is a rare ursid hybrid resulting from a crossbreeding of a brown bear and a polar bear. It has occurred both in captivity and in the wild. In 2006, the occurrence of this hybrid in nature was confirmed by testing the DNA of a strange-looking bear that had been shot in the Canadian Arctic, and seven more hybrids have since been confirmed in the same region, all descended from a single female polar bear. Previously, the hybrid had been produced in zoos and was considered a "cryptid" (a hypothesized animal for which there is no scientific proof of existence in the wild).
Analyses of the genomes of bears have shown that introgression between species was widespread during the evolution of the genus Ursus, including the introgression of polar bear DNA introduced to brown bears during the Pleistocene.
A bear shot in autumn 1986 in Michigan, US, was thought by some to be a grizzly/American black bear hybrid, due to its unusually large size and its proportionately larger braincase and skull. DNA testing was unable to determine whether it was a large American black bear or a grizzly bear.
Brown bear Evolution and taxonomy articles: 33
The brown bear is the most variable in size of modern bears. The typical size depends upon which population it is from, and most accepted subtypes vary widely in size. This is in part due to sexual dimorphism, as male brown bears average at least 30% larger in most subtypes. Individual bears also vary in size seasonally, weighing the least in spring due to lack of foraging during hibernation, and the most in late fall, after a period of hyperphagia to put on additional weight to prepare for hibernation. Therefore, a bear may need to be weighed in both spring and fall to get an idea of its mean annual weight.
The normal range of physical dimensions for a brown bear is a head-and-body length of 1.4 to 2.8 m (4 ft 7 in to 9 ft 2 in) and a shoulder height of 70 to 153 cm (2 ft 4 in to 5 ft 0 in). The tail is relatively short, as in all bears, ranging from 6 to 22 cm (2.4 to 8.7 in) in length. The smallest brown bears, females during spring among barren-ground populations, can weigh so little as to roughly match the body mass of males of the smallest living bear species, the sun bear (Helarctos malayanus), while the largest coastal populations attain sizes broadly similar to those of the largest living bear species, the polar bear. Interior brown bears are generally smaller than is often perceived, being around the same weight as an average lion, at an estimate average of 180 kg (400 lb) in males and 135 kg (298 lb) in females, whereas adults of the coastal populations weigh about twice as much. The average weight of adult male bears from 19 populations, from around the world and various subspecies (including both large- and small-bodied subspecies), was found to be 217 kg (478 lb) while adult females from 24 populations were found to average 152 kg (335 lb).
Brown bears are often not fully brown. They have long, thick fur, with a moderately long mane at the back of the neck which varies somewhat across the types. In India, brown bears can be reddish with silver-tipped hairs, while in China brown bears are bicolored, with a yellowish-brown or whitish collar across the neck, chest and shoulders. Even within well-defined subspecies, individuals may show highly variable hues of brown. North American grizzlies can be dark brown (almost black) to cream (almost white) or yellowish-brown and often have darker-colored legs. The common name "grizzly" stems from their typical coloration, with the hairs on their back usually being brownish-black at the base and whitish-cream at the tips, giving them their distinctive "grizzled" color. Apart from the cinnamon subspecies of the American black bear (U. americanus cinnamonum), the brown bear is the only modern bear species to typically appear truly brown. The winter fur is very thick and long, especially in northern subspecies, and can reach 11 to 12 centimetres (4 to 5 in) at the withers. The winter hairs are thin, yet rough to the touch. The summer fur is much shorter and sparser and its length and density varies geographically.
Cranial morphology and size
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 (Ursus thibetanus): 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 females 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 brown 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. The teeth of brown bears reflect their dietary plasticity and are broadly similar to other bears, excluding the two most herbivorous living bears, the giant panda (Ailuropoda melanoleuca) and the spectacled bear (Tremarctos ornatus), which have blunt, small premolars (ideal for grinding down fibrous plants) compared to the jagged premolars of ursid bears that at least seasonally often rely on flesh as a food source. The teeth are reliably larger than American black bears, but average smaller in molar length than polar bears. Brown bears have the broadest skull of any extant ursine bear; only the aforementioned most herbivorous living bears exceed them in relative breadth of the skull. Another extant ursine bear, the sloth bear (Melursus ursinus), has a proportionately longer skull than the brown bear and can match the skull length of even large brown bear subtypes, presumably as an aid for foraging heavily on insect colonies for which a long muzzle is helpful as an evolved feature in several unrelated mammalian groups.
Claws and feet
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 may measure 7 to 10 centimetres (2.8 to 3.9 in) along the curve. 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 (Ursus americanus). The claws are blunt, while those of a black bear are sharp. Due to their claw structure, in addition to their excessive weight, adult brown bears cannot typically climb trees as well as both species of black bear, although in rare cases adult female brown bears have been seen in trees. The claws of a polar bear are also quite different, being notably shorter but broader with a strong curve and sharper point, presumably both as an aid to traveling over ice (sometimes nearly vertically) and procuring active prey. The paws of the brown bear are quite large. The rear feet of adult bears have been found to typically measure 21 to 36 cm (8.3 to 14.2 in) long, while the forefeet tend to measure about 40% less in length. All four feet in average sized brown bears tend to be about 17.5 to 20 cm (6.9 to 7.9 in) in width. In large coastal or Kodiak bear males, the hindfoot may measure up to 40 cm (16 in) in length, 28.5 cm (11.2 in) in width, while outsized Kodiak bears having had confirmed measurements of up to 46 cm (18 in) along their rear foot. Brown bears are the only extant bears with a hump at the top of their shoulder, which is made entirely of muscle, this feature having developed presumably for imparting more force in digging, which is habitual during foraging for most bears of the species and also used heavily in den construction prior to hibernation.
Brown bear Description articles: 14
Distribution and habitat
Brown bears were once native to Europe, much of Asia, the Atlas Mountains of Africa, and North America, but are now extirpated in some areas, and their populations have greatly decreased in other areas. There are approximately 200,000 brown bears left in the world. The largest populations are in Russia with 120,000, the United States with 32,500, and Canada with around 25,000. About 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 the belief some brown bears may be present in Mexico and the Atlas Mountains of North Africa, both are almost certainly extinct. The last known Mexican grizzly bear was shot in 1960, while the Atlas bear has been extinct since the 19th century. In Europe, there are 14,000 brown bears in ten fragmented populations, from Spain (estimated at only 20–25 animals in the Pyrenees in 2010, in a range shared between Spain, France and Andorra, and some 210 animals in Asturias, Cantabria, Galicia and León, in the Picos de Europa and adjacent areas in 2013) in the west, to Russia in the east, and from Sweden and Finland in the north to Romania (4000–5000), Bulgaria (900–1200), Slovakia (with about 600–800 animals), Slovenia (500–700 animals) and Greece (with about 200 animals) in the south. They are extinct in the British Isles, endangered in France, and threatened in Spain and 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, although declining alarmingly due to overhunting. There is also a smaller brown bear population in the Carpathian Mountains in Ukraine (estimated at about 200 in 2005), Slovakia and Poland (estimated at about 100 in 2009 in the latter country). The total Carpathian population is estimated at about 8,000. Northern Europe is home to a large bear population, with an estimated 2,500 (range 2,350–2,900) in Sweden, about 1,600 in Finland, about 700 in Estonia 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 northeast Italy, Slovenia, Croatia, Bosnia and Herzegovina, Serbia, Montenegro, Macedonia, Albania, Bulgaria and Greece.
Brown bears live in Alaska, east through the Yukon and Northwest Territories, south through British Columbia and through the western half of Alberta. The Alaskan population is estimated at a healthy 32,000 individuals. 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 northcentral 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 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 primarily throughout Russia, thence more spottily southwest to parts of the Middle East, to as far south as southwestern Iran, and to the southeast in a small area of Northeast China, Western China, and parts of North Korea, Pakistan, Afghanistan and India. They can also be found on the Japanese island of Hokkaidō, which holds the largest number of non-Russian brown bears in eastern Asia with about 2,000–3,000 animals.
The population of brown bears in the Pyrenees mountain range between Spain and France is extremely low, estimated at 14 to 18, with a shortage of females. Their rarity in this area has led biologists to release bears, mostly female, from Slovenia in spring 2006 to reduce the imbalance and preserve the species' presence in the area. The bears were released despite protests from French farmers. A small population of brown bears (Ursus arctos marsicanus) still lives in central Italy (the Apennine Mountains, Abruzzo and Latium), with no more than 50–60 individuals, protected by strong laws, but endangered by the human presence in the area. In 2020, a film crew working in Natural Park O Invernadeiro in Ourense, Galicia recorded the first brown bear in Northern Spain in 150 years.
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.
This species inhabits the broadest range of habitats of any living bear species. They seem to have no altitudinal preferences and have been recorded from sea level to an elevation of 5,000 m (16,000 ft) (the latter in the Himalayas). In most of their range, brown bears generally seem to prefer semiopen country, with a scattering of vegetation that can allow them a resting spot during the day. However, they have been recorded as inhabiting every variety of northern temperate forest known to occur. North American brown bears, or grizzly bears, generally seem to prefer open or semi-open landscapes, with the species once having been common on the Great Plains and continues to occur in sizeable numbers in tundra and coastal estuaries and islands. Variable numbers still occur in prairie areas of the northern Rocky Mountains (mostly in Canada but some in the contiguous United States). In western Eurasia, they inhabit mostly mountainous woodlands, in ranges such as the Alps, the Pyrenees and the Caucasus, though they may have been driven into more wooded, precipitous habitats due to the prior extensive persecution of the species in some regions. Desolate parts of northern and eastern Europe, like large patches of Scandinavia and the Carpathian Mountains, have always been quite heavily forested and have maintained relatively stable populations of bears, indicating that the brown bears here are well-adapted to forest-dwelling. In Central Asia, human disturbances are minimal as this area has a harsher environment and is more sparsely populated. In this part of the world, bears may be found in steppe, alpine meadows and even desert edge. In Siberia, the species seems well-adapted to living in denser pine forests. Eastern Russian forests hold arguably the largest number of brown bears in the world outside of possibly Alaska and northeastern Canada. It is thought the Eurasian bears which colonized America were tundra-adapted and the species is sometimes found around sub-Arctic ice fields. 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.
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. As of 2012[update], this and the American black bear are the only bear species not classified as threatened by the IUCN. However, the California grizzly bear, Ungavan brown bear, Atlas bear and Mexican grizzly bear, as well as brown bear populations in the Pacific Northwest, were hunted to extinction in the 19th and early 20th centuries and many of the southern Asian subspecies are highly endangered. The Syrian brown bear (Ursus arctos syriacus) is very rare and it has been extirpated from more than half of its historic range. One of the smallest-bodied subspecies, the Himalayan brown bear (Ursus arctos isabellinus), is critically endangered, occupying only 2% of its former range and threatened by uncontrolled poaching for its body parts. The Marsican brown bear in central Italy is believed to have a population of just 50–60 bears.
Brown bear Distribution and habitat articles: 62
Behavior and life history
The brown bear is often described as nocturnal. However, it frequently seems to peak in activity in the morning and early evening hours. Studies have shown that activity throughout the range can occur at nearly any time of night or day, with bears who dwell in areas with more extensive human contact being more likely to be fully nocturnal. Furthermore, yearling and newly independent bears are more likely to be active diurnally and many adult bears in low-disturbance areas are largely crepuscular. In summer through autumn, a brown bear can double its weight from the spring, gaining up to 180 kg (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 during the winter months. Hibernation dens may consist of any spot that provides cover from the elements and that can accommodate their bodies, such as a cave, crevice, cavernous tree roots, or hollow logs.
Brown bears have one of the largest brains of any extant carnivoran relative to their body size and have been shown to engage in tool use (e.g., using a barnacle-covered rock to scratch its neck), which requires advanced cognitive abilities. This species is mostly solitary, although bears may gather in large numbers at major food sources (e.g., open garbage dumps or rivers holding spawning salmon) and form social hierarchies based on age and size. Adult male bears are particularly aggressive and are avoided by adolescent and subadult males, both at concentrated feeding opportunities and chance encounters. Female bears with cubs rival adult males in aggression and are much more intolerant of other bears than single females. Young adolescent males tend to be least aggressive and have been observed in nonantagonistic interactions with each other. Dominance between bears is asserted by making a frontal orientation, showing off canines, muzzle twisting and neck stretching to which a subordinate will respond with a lateral orientation, by turning away and dropping the head and by sitting or lying down. During combat, bears use their paws to strike their opponents in the chest or shoulders and bite the head or neck. In his Great Bear Almanac, Gary Brown lists 11 different sounds bears produce in nine 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.
Brown bears usually occur over vast home ranges; however, they are not highly territorial. Several adult bears often roam freely over the same vicinity without issue, unless rights to a fertile female or food sources are being contested. Males always cover more area than females each year. Despite their lack of traditional territorial behavior, adult males can seem to have a "personal zone" in which other bears are not tolerated if they are seen. Males always wander further than females, due to both increasing access to females and food sources, while females are advantaged by smaller territories in part since it decreases the likelihood of encounters with male bears who may endanger their cubs. In areas where food is abundant and concentrated, such as coastal Alaska, home ranges for females are up to 24 km2 (9.3 sq mi) and for males are up to 89 km2 (34 sq mi). Similarly, in British Columbia, bears of the two sexes travel relatively compact home ranges of 115 km2 (44 sq mi) and 318 km2 (123 sq mi). In Yellowstone National Park, home ranges for females are up to 281 km2 (108 sq mi) and up to 874 km2 (337 sq mi) for males. In Romania, the largest home range was recorded for adult males (3,143 km2, 1214 sq mi). In the central Arctic of Canada, where food sources are quite sparse, home ranges range up to 2,434 km2 (940 sq mi) in females and 8,171 km2 (3,155 sq mi) in males.
A study of male-inherited Y chromosome DNA sequence found that brown bears, over the past few 10,000 years, have shown strong male-biased dispersal. That study found surprisingly similar Y chromosomes in brown bear populations as far apart as Norway and coastal Alaska, indicating extensive gene flow across Eurasia and North America. Notably, this contrasts with genetic signals from female-inherited mitochondrial DNA (mtDNA), where brown bears of different geographic regions typically show strong differences in their mtDNA, a result of female philopatry.
The mating season is from mid-May to early July, shifting later the further north the bears are found. Being serially monogamous, brown bears remain with the same mate from a couple of days to a couple of weeks. Outside of this narrow time frame, adult male and female brown bears show no sexual interest in each other. Females mature sexually between the age of four and eight years of age, with an average age at sexual maturity of 5.2–5.5 years old, while males first mate about a year later on average, when they are large and strong enough to successfully compete with other males for mating rights. Males will try to mate with as many females as they can; usually a successful one mates with two females in a span of one to three weeks. The adult female brown bear is similarly promiscuous, mating with up to four, rarely even eight, males while in heat and potentially breeding with two males in a single day. Females come into oestrus on average every three to four years, with a full range of 2.4 to 5.7 years. The urine markings of a female in oestrus can attract several males via scent. Paternity DNA tests have shown that up to 29% of cubs in a litter will be from two to three different males. Dominant males may try to sequester a female for her entire oestrus period of approximately two weeks, but usually are unable to retain her for the entire time. Copulation is vigorous and prolonged and can last up to an hour, although the mean time is about 23–24 minutes.
Males 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 freely 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 while gestating, the embryo does not implant and is reabsorbed into the body. There have been cases of brown bears with as many as six cubs, although the average litter size is one to three, with more than four being considered uncommon. There are records of females sometimes adopting stray cubs or even trading or kidnapping cubs when they emerge from hibernation (a larger female may claim cubs away from a smaller one). Older and larger females within a population 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 and hairless and may weigh from 350 to 510 g (0.77 to 1.12 lb), again reportedly based on the age and condition of the mother. 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 kg (15 to 20 lb) and have developed enough to follow her over long distances and begin to forage for solid food.
The cubs are fully dependent on the mother and a close bond is formed. During the dependency stage, the cubs learn (rather than inherit as instincts from birth) survival techniques, such as which foods have the highest nutritional value and where to obtain them; how to hunt, fish and defend themselves; and where to den. Increased brain size in large carnivores has been positively linked to whether a given species is solitary, as is the brown bear, or raises their offspring communally, thus female brown bears have relatively large, well-developed brains, presumably key in teaching behavior. The cubs learn by following and imitating their mother's actions during the period they are with her. Cubs remain with their mother for an average of 2.5 years in North America, uncommonly being independent as early as 1.5 years of age or as late as 4.5 years of age. The stage at which independence is attained may generally be earlier in some parts of Eurasia, as the latest date which mother and cubs were together was 2.3 years, most families separated in under two years in a study from Hokkaido and in Sweden most cubs on their own were still yearlings. Brown bears practice infanticide, as an adult male bear may kill the cubs of a female bear. When an adult male brown bear kills a cub, it is usually because he is trying to bring the female into oestrus, as she will enter that state within two to four days after the death of her cubs. Cubs flee up a tree, if available, when they see a strange male bear and the mother often successfully defends them, even though the male may be twice as heavy as she, although females have been known to lose their lives in these confrontations.
The brown bear is one of the most omnivorous animals in the world and has been recorded as consuming the greatest variety of foods of any bear. Throughout life, this species is regularly curious about the potential of eating virtually any organism or object that they encounter. Food that is both abundant and easily accessed or caught is preferred. Their jaw structure has evolved to fit their dietary habits. Their diet varies enormously throughout their differing areas based on opportunity.
Despite their reputation, most brown bears are not highly carnivorous, as they derive up to 90% of their dietary food energy from vegetable matter. They often feed on a variety of plant life, including berries, grasses, flowers, acorns and pine cones, as well as fungi such as mushrooms. Among all bears, brown bears are uniquely equipped to dig for tough foods such as roots and shoots. They use their long, strong claws to dig out earth to reach the roots and their powerful jaws to bite through them. In spring, winter-provided carrion, grasses, shoots, sedges and forbs are the dietary mainstays for brown bears internationally. Fruits, including berries, become increasingly important during summer and early autumn. Roots and bulbs become critical in autumn for some inland bear populations if fruit crops are poor. They will also commonly consume animal matter, which in summer and autumn may regularly be in the form of insects, larvae and grubs, including beehives. Bears in Yellowstone eat an enormous number of moths during the summer, sometimes as many as 40,000 Army cutworm moths in a single day, and may derive up to half of their annual food energy from these insects. Brown bears living near coastal regions will regularly eat crabs and clams. In Alaska, bears along the beaches of estuaries regularly dig through the sand for clams. This species may eat birds and their eggs, including almost entirely ground- or rock-nesting species. The diet may be supplemented by rodents or similar smallish mammals, including marmots, ground squirrels, mice, rats, lemmings and voles. With particular regularity, bears in Denali National Park will wait at burrows of Arctic ground squirrels hoping to pick off a few of the 1 kg (2.2 lb) rodents.
In the Kamchatka peninsula and several parts of coastal Alaska, brown bears feed mostly on spawning salmon, whose nutrition and abundance explain the enormous size of the bears in these areas. The fishing techniques of bears are well-documented. They often congregate around falls when the salmon are forced to breach the water, at which point the bears will try to catch the fish in mid-air (often with their mouths). They will also wade into shallow waters, hoping to pin a slippery salmon with their claws. While they may eat almost all the parts of the fish, bears at the peak of spawning, when there is usually a glut of fish to feed on, may eat only the most nutrious parts of the salmon (including the eggs and head) and then indifferently leave the rest of the carcass to scavengers, which can include red foxes, bald eagles, common ravens and gulls. Despite their normally solitary habits, brown bears will gather rather closely in numbers at good spawning sites. The largest and most powerful males claim the most fruitful fishing spots and bears (especially males) will sometimes fight over the rights to a prime fishing spot.
Beyond the regular predation of salmon, most brown bears are not particularly active predators. While perhaps a majority of bears of the species will charge at large prey at one point in their lives and most eat carrion, many predation attempts start with the bear clumsily and half-heartedly pursuing the prey and end with the prey escaping alive. On the other hand, some brown bears are quite self-assured predators who habitually pursue and catch large prey items. Such bears are usually taught how to hunt by their mothers from an early age. Large mammals preyed on can include various ungulate species such as elk, moose, caribou, muskoxen and wild boar. When brown bears attack these large animals, they usually target young or infirm ones, as they are easier to catch. Typically when hunting (especially with young prey), the bear pins its prey to the ground and then immediately tears and eats it alive. It will also bite or swipe some prey to stun it enough to knock it over for consumption. To pick out young or infirm individuals, bears will charge at herds so the slower-moving and more vulnerable individuals will be made apparent. Brown bears may also ambush young animals by finding them via scent. When emerging from hibernation, brown bears, whose broad paws allow them to walk over most ice and snow, may pursue large prey such as moose whose hooves cannot support them on encrusted snow. Similarly, predatory attacks on large prey sometimes occur at riverbeds, when it is more difficult for the prey specimen to run away due to muddy or slippery soil. On rare occasions, while confronting fully-grown, dangerous prey, bears kill them by hitting with their powerful forearms, which can break the necks and backs of large creatures such as adult moose and adult bison. They also feed on carrion, and use their size to intimidate other predators, such as wolves, cougars, tigers, and American black bears from their kills. Carrion is especially important in the early spring (when the bears are emerging from hibernation), much of it comprised by winter-killed big game. Cannibalism is not unheard of, though predation is not normally believed to be the primary motivation when brown bears attack each other.
When forced to live in close proximity with humans and their domesticated animals, bears may potentially predate any type of domestic animal. Among these, domestic cattle are sometimes exploited as prey. Cattle are bitten on the neck, back or head and then the abdominal cavity is opened for eating. Plants and fruit farmed by humans are readily consumed as well, including corn, wheat, sorghum, melons and any form of berries. They will also feed at domestic bee farms, readily consuming both honey and the contents of the honey bee colony. Human foods and trash or refuse is eaten when possible. When an open garbage dump was kept in Yellowstone, brown bears were one of the most voracious and regular scavengers. The dump was closed after both brown and American black bears came to associate humans with food and lost their natural fear of them.
Interspecific predatory relationships
Adult bears are generally immune to predatory attacks except from tigers and other bears. Siberian tigers prefer preying on young Ussuri brown bears, but smaller adult female brown bears outside their dens may also be taken, generally when lethargic from hibernation. Of 44 recorded encounters between the two predators, 20 resulted in confrontations; in 50% of these, the bears were killed, in 27% the tigers were killed, and 23% of the cases ended with both animals surviving and parting ways. Some bears emerging from hibernation seek out tigers in order to steal their kills. Some large brown bears may actually benefit from the tiger's presence by appropriating tiger kills that the bears may not be able to successfully hunt themselves and follow tiger tracks. Geptner et al. (1972) stated bears are generally afraid of tigers and change their path after coming across tiger trails. In the winters of 1970–1973, Yudakov and Nikolaev recorded 1 case of brown bear showing no fear of the tigers and another case of brown bear changing path upon crossing tiger tracks. Other researchers have observed bears following tiger tracks for various reasons.
Brown bears regularly intimidate wolves to drive them away from their kills. In Yellowstone National Park, bears pirate wolf kills so often, Yellowstone's Wolf Project director Doug Smith wrote, "It's not a matter of if the bears will come calling after a kill, but when." Despite the high animosity between the two species, most confrontations at kill sites or large carcasses end without bloodshed on either side. Though conflict over carcasses is common, on rare occasions, the two predators tolerate each other on the same kill. To date, there is a single case of fully-grown wolves being killed by a grizzly bear. Given the opportunity, however, both species will prey on the other's cubs. Conclusively, the individual power of the bear against the collective strength of the wolf pack usually results in a long battle for kills or domination.
In some areas, grizzly bears also regularly displace cougars from their kills. Cougars kill small bear cubs on rare occasions, but there was one report of a bear killing a cougar of unknown age and condition between 1993 and 1996. Smaller carnivorous animals, including coyotes, wolverines, lynxes, and any other sympatric carnivores or raptorial birds, are dominated by grizzly bears and generally avoid direct interactions with them, unless attempting to steal scraps of food. However, wolverines have been persistent enough to fend off a grizzly bear as much as ten times their weight off a kill. There is one record of a golden eagle predating on a brown bear cub.
Brown bears usually dominate other bear species in areas where they coexist. Due to their smaller size, American black bears are at a competitive disadvantage to grizzly bears in open, unforested areas. Although displacement of black bears by grizzly bears has been documented, actual interspecific killing of black bears by grizzlies has only occasionally been reported. Confrontation is mostly avoided due to the black bear's diurnal habits and preference for heavily forested areas, as opposed to the grizzly's largely nocturnal habits and preference for open spaces. Brown bears may also kill Asian black bears, though the latter species probably largely avoids conflicts with the brown bear, due to similar habits and habitat preferences to the American black species. They will eat the fruit dropped by the Asian black bear from trees, as they themselves are too large and cumbersome to climb. Improbably, in the Himalayas Brown bears are reportedly intimidated by Asian black bears in confrontations.
There has been a recent increase in interactions between brown bears and polar bears, theorized to be caused by climate change. Brown and grizzly bears have been seen moving increasingly northward into territories formerly claimed by polar bears. They tend to dominate polar bears in disputes over carcasses, and dead polar bear cubs have been found in brown bear dens.
Longevity and mortality
The brown bear has a naturally long life. Wild females have been observed reproducing up to 28 years of age, which is the oldest known age for reproduction of any ursid in the wild. The peak reproductive age for females ranges from four to 20 years old. The lifespan of brown bears of both sexes within minimally hunted populations is estimated at an average of 25 years. The oldest wild brown bear on record was nearly 37 years old. The oldest recorded female in captivity was nearly 40 years old, while males in captivity have been verified to live up to 47 years, with one captive male possibly attaining 50 years of age.
While male bears potentially live longer in captivity, female grizzly bears have a greater annual survival rate than males within wild populations per a study done in the Greater Yellowstone Ecosystem. Annual mortality for bears of any age is estimated at around 10% in most protected areas; however, the average annual mortality rate rises to an estimated 38% in hunted populations. Around 13% to 44% of cubs die within their first year even in well-protected areas. Mortality rates of 75–100% among the cubs of any given year are not uncommon. Beyond predation by large predators including wolves, Siberian tigers and other brown bears, starvation and accidents also claim the lives of cubs. Studies have indicated that the most prevalent source of mortality for first-year cubs is malnutrition. By the second and third years of their lives, the annual mortality rate among cubs in the care of their mothers drops to 10-15%.
Even in populations living in protected areas, humans are still the leading cause of mortality for brown bears. The largest amount of legalized brown bear hunting occurs in Canada, Finland, Russia, Slovakia and Alaska. Hunting is unregulated in many areas within the range of the brown bear. Even where hunting is legally permitted, most biologists feel that the numbers hunted are excessive considering the low reproduction rate and sparse distribution of the species. Brown bears are also killed in collisions with automobiles, which is a significant cause of mortality in the United States and Europe.