Wikipedia

Bear

"Bear cub" redirects here. For the 2004 film, seeBear Cub.
For other uses, seeBear (disambiguation).

Bearsarecarnivoranmammalsof thefamilyUrsidae(/ˈɜːrsɪdiː,-daɪ/). They are classified ascaniforms,or doglike carnivorans. Although only eightspeciesof bears are extant, they are widespread, appearing in a wide variety ofhabitatsthroughout most of the Northern Hemisphere and partially in the Southern Hemisphere. Bears are found on the continents ofNorth America,South America,andEurasia.Common characteristics of modern bears include large bodies with stocky legs, long snouts, small rounded ears, shaggy hair,plantigradepaws with five nonretractile claws, and short tails.

Bears
Temporal range:38–0MaLateEocene– Recent
Brown bear(Ursus arctos)
Scientific classificationEdit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Carnivora
Superfamily: Ursoidea
Family: Ursidae
G. Fischer de Waldheim,1817
Type genus
Ursus
Subfamilies

While thepolar bearis mostlycarnivorous,and thegiant pandais mostlyherbivorous,the remaining six species areomnivorouswith varying diets. With the exception ofcourtingindividuals and mothers with their young, bears are typicallysolitary animals.They may bediurnalornocturnaland have an excellentsense of smell.Despite their heavy build and awkward gait, they are adept runners, climbers, and swimmers. Bears use shelters, such as caves and logs, as their dens; most species occupy their dens during the winter for a long period ofhibernation,up to 100 days.

Bears have been hunted sinceprehistorictimes fortheir meatand fur; they have also been used forbear-baitingand other forms of entertainment, such as beingmade to dance.With their powerful physical presence, they play a prominent role inthe arts,mythology,and other cultural aspects of various human societies. In modern times, bears have come under pressure through encroachment on their habitats and illegal trade in bear parts, including the Asianbile bearmarket. TheIUCNlists six bear species asvulnerableorendangered,and evenleast concernspecies, such as thebrown bear,are at risk ofextirpationin certain countries. Thepoachingand international trade of these most threatened populations are prohibited, but still ongoing.

Etymology

The English word "bear" comes fromOld Englishberaand belongs to a family of names for the bear inGermanic languages,such as Swedishbjörn,also used as a first name. This form is conventionally said to be related to aProto-Indo-Europeanword for "brown", so that "bear" would mean "the brown one".[1][2]However,Ringenotes that while this etymology is semantically plausible, a word meaning "brown" of this form cannot be found in Proto-Indo-European. He suggests instead that "bear" is from the Proto-Indo-European word*ǵʰwḗr- ~ *ǵʰwér"wild animal".[3]This terminology for the animal originated as ataboo avoidanceterm: proto-Germanic tribes replaced their original word for bear—arkto—with this euphemistic expression out of fear that speaking the animal's true name might cause it to appear.[4][5]According to authorRalph Keyes,this is the oldest knowneuphemism.[6]

Bear taxon names such asArctoideaandHelarctoscome from the ancient Greek ἄρκτος (arktos), meaning bear,[7]as do the names "arctic"and"antarctic",via the name of theconstellationUrsa Major,the "Great Bear", prominent in the northern sky.[8]

Bear taxon names such as Ursidae andUrsuscome from LatinUrsus/Ursa,he-bear/she-bear.[8]The female first name "Ursula",originally derived from a Christiansaint's name, means "little she-bear" (diminutive of Latinursa). In Switzerland, the male first name "Urs" is especially popular, while the name of the canton and city ofBernis by legend derived fromBär,German for bear. The Germanic nameBernard(including Bernhardt and similar forms) means "bear-brave", "bear-hardy", or "bold bear".[9][10]The Old English nameBeowulfis akenning,"bee-wolf", for bear, in turn meaning a brave warrior.[11]

Taxonomy

Further information:List of ursids

The family Ursidae is one of nine families in the suborderCaniformia,or "doglike" carnivorans, within theorderCarnivora.Bears' closest living relatives are thepinnipeds,canids,andmusteloids[12](some scholars formerly argued that bears are directly derived from canids and should not be classified as a separate family).[13]Modern bears comprise eight species in three subfamilies:Ailuropodinae(monotypic with thegiant panda),Tremarctinae(monotypic with thespectacled bear), andUrsinae(containing six species divided into one to three genera, depending on the authority). Nuclear chromosome analysis show that thekaryotypeof the six ursine bears is nearly identical, each having 74chromosomes(seeUrsid hybrid), whereas the giant panda has 42 chromosomes and the spectacled bear 52. These smaller numbers can be explained by the fusing of some chromosomes, and the banding patterns on these match those of the ursine species, but differ from those of procyonids, which supports the inclusion of these two species in Ursidae rather than inProcyonidae,where they had been placed by some earlier authorities.[14]

Evolution

Plithocyon armagnacensisskull, a member of the extinct subfamily Hemicyoninae from theMiocene

The earliest members of Ursidae belong to the extinct subfamily Amphicynodontinae, includingParictis(lateEoceneto early middleMiocene,38–18Mya) and the slightly youngerAllocyon(earlyOligocene,34–30 Mya), both from North America. These animals looked very different from today's bears, being small andraccoon-like in overall appearance, with diets perhaps more similar to that of abadger.Parictisdoes not appear in Eurasia and Africa until the Miocene.[15]It is unclear whether late-Eocene ursids were also present in Eurasia, although faunal exchange across theBering land bridgemay have been possible during a major sea level low stand as early as the late Eocene (about 37 Mya) and continuing into the early Oligocene.[16]European genera morphologically very similar toAllocyon,and to the much younger AmericanKolponomos(about 18 Mya),[17]are known from the Oligocene, includingAmphicticepsandAmphicynodon.[16]There has been various morphological evidence linking amphicynodontines withpinnipeds,as both groups were semi-aquatic, otter-like mammals.[18][19][20]In addition to the support of the pinniped–amphicynodontine clade, other morphological and some molecular evidence supports bears being the closest living relatives to pinnipeds.[21][22][23][19][24][20]

Life restoration ofArctotherium bonariense

The raccoon-sized, dog-likeCephalogaleis the oldest-known member of the subfamilyHemicyoninae,which first appeared during the middle Oligocene in Eurasia about 30 Mya.[16]The subfamily includes the younger generaPhoberocyon(20–15 Mya), andPlithocyon(15–7 Mya). ACephalogale-like species gave rise to the genusUrsavusduring the early Oligocene (30–28 Mya); this genus proliferated into many species in Asia and is ancestral to all living bears. Species ofUrsavussubsequently entered North America, together withAmphicynodonandCephalogale,during the early Miocene (21–18 Mya). Members of the living lineages of bears diverged fromUrsavusbetween 15 and 20 Mya,[25][26]likely via the speciesUrsavus elmensis.Based on genetic and morphological data, the Ailuropodinae (pandas) were the first to diverge from other living bears about 19 Mya, although no fossils of this group have been found before about 11 Mya.[27][28]

The New World short-faced bears (Tremarctinae) differentiated from Ursinae following a dispersal event into North America during the mid-Miocene (about 13 Mya).[27]Theyinvaded South America(≈2.5 or 1.2 Ma) following formation of theIsthmus of Panama.[29]Their earliest fossil representative isPlionarctosin North America (c. 10–2 Ma). This genus is probably the direct ancestor to theNorth American short-faced bears(genusArctodus), theSouth American short-faced bears(Arctotherium), and the spectacled bears,Tremarctos,represented by both an extinct North American species (T. floridanus), and the lone surviving representative of the Tremarctinae, the South Americanspectacled bear(T. ornatus).[16]

Fossil of thecave bear(Ursus spelaeus), a relative of the brown bear and polar bear from thePleistoceneepochin Europe

The subfamily Ursinae experienced a dramatic proliferation of taxa about 5.3–4.5 Mya, coincident with major environmental changes; the first members of the genusUrsusappeared around this time. Thesloth bearis a modern survivor of one of the earliest lineages to diverge during this radiation event (5.3 Mya); it took on its peculiar morphology, related to its diet of termites and ants, no later than by the early Pleistocene. By 3–4 Mya, the speciesUrsus minimusappears in the fossil record of Europe; apart from its size, it was nearly identical to today'sAsian black bear.It is likely ancestral to all bears within Ursinae, perhaps aside from the sloth bear. Two lineages evolved fromU. minimus:the black bears (including thesun bear,the Asian black bear, and theAmerican black bear); and the brown bears (which includes thepolar bear). Modernbrown bearsevolved fromU. minimusviaUrsus etruscus,which itself is ancestral to the extinctPleistocenecave bear.[27]Species of Ursinae have migrated repeatedly into North America from Eurasia as early as 4 Mya during the early Pliocene.[30][31]The polar bear is the most recently evolved species and descended from a population of brown bears that became isolated in northern latitudes by glaciation 400,000 years ago.[32]

Phylogeny

The relationship of the bear family with other carnivorans is shown in the followingphylogenetic tree,which is based on themolecular phylogenetic analysisof six genes in Flynn (2005)[33]with the musteloids updated following the multigene analysis of Law et al. (2018).[34]

Carnivora

Note that although they are called "bears" in some languages,red pandasandraccoons and their close relativesare not bears, but rathermusteloids.[33]

There are two phylogenetic hypotheses on the relationships among extant and fossil bear species. One is all species of bears are classified in seven subfamilies as adopted here and related articles:Amphicynodontinae,Hemicyoninae,Ursavinae,Agriotheriinae,Ailuropodinae,Tremarctinae,andUrsinae.[13][35][36][37]Below is a cladogram of the subfamilies of bears after McLellan and Reiner (1992)[13]and Qiuet al.(2014):[37][clarification needed]

Ursidae

The second alternative phylogenetic hypothesis was implemented by McKenna et al. (1997) to classify all the bear species into the superfamilyUrsoidea,with Hemicyoninae and Agriotheriinae being classified in the family "Hemicyonidae".[38]Amphicynodontinae under this classification were classified as stem-pinnipedsin the superfamilyPhocoidea.[38]In the McKenna and Bell classification both bears and pinnipeds are in a parvorder ofcarnivoranmammals known asUrsida,along with the extinct bear dogs of the familyAmphicyonidae.[38]Below is the cladogram based on McKenna and Bell (1997) classification:[38][clarification needed]

Ursida


A possible phylogeny based on completemitochondrial DNAsequences from Yu et al. (2007).[39]
Ursidae

Giant panda(Ailuropoda melanoleuca)

Spectacled bear(Tremarctos ornatus)

Ursinae

Sloth bear(Melursus ursinus)

Sun bear(Helarctos malayanus)

Asian black bear(Ursus thibetanus)

American black bear(Ursus americanus)

Polar bear(Ursus maritimus)

Brown bear(Ursus arctos)

The polar bear and the brown bear form a close grouping, while the relationships of the other species are not very well resolved.[14]
A more recent phylogeny based on the genetic study of Kumar et al. (2017).[40]
Ursidae

Giant panda(Ailuropoda melanoleuca)

Spectacled bear(Tremarctos ornatus)

Ursinae

Sloth bear(Melursus ursinus)

Sun bear(Helarctos malayanus)

Asian black bear(Ursus thibetanus)

American black bear(Ursus americanus)

Polar bear(Ursus maritimus)

Brown bear(Ursus arctos)

The study concludes that Ursine bears originated around five million years ago and show extensive hybridization of species in their lineage.[40]


Physical characteristics

Size

Polar bear (left) and sun bear, the largest and smallest species respectively, on average

The bear family includes the most massive extant terrestrial members of the order Carnivora.[a]The polar bear is considered to be the largest extant species,[42]with adult males weighing 350–700 kg (770–1,540 lb) and measuring 2.4–3 m (7 ft 10 in – 9 ft 10 in) in total length.[43]The smallest species is the sun bear, which ranges 25–65 kg (55–143 lb) in weight and 100–140 cm (39–55 in) in length.[44]PrehistoricNorthandSouth American short-faced bearswere the largest species known to have lived. The latter estimated to have weighed 1,600 kg (3,500 lb) and stood 3.4 m (11 ft) tall.[45][46]Body weight varies throughout the year in bears of temperate and arctic climates, as they build up fat reserves in the summer and autumn and lose weight during the winter.[47]

Morphology

Unlike most othercarnivorans,bears haveplantigradefeet. Drawing byRichard Owen,1866.

Bears are generally bulky and robust animals with short tails. They aresexually dimorphicwith regard to size, with males typically being larger.[48][49]Larger species tend to show increased levels of sexual dimorphism in comparison to smaller species.[49]Relying as they do on strength rather than speed, bears have relatively short limbs with thick bones to support their bulk. Theshoulder bladesand thepelvisare correspondingly massive. The limbs are much straighter than those of thebig catsas there is no need for them to flex in the same way due to the differences in their gait. The strong forelimbs are used to catch prey, excavate dens, dig out burrowing animals, turn over rocks and logs to locate prey, and club large creatures.[47]

Despite beingquadrupeds,bears can stand and sit as humans do, as demonstrated by thisAmerican black bear.

Unlike most other land carnivorans, bears areplantigrade.They distribute their weight toward the hind feet, which makes them look lumbering when they walk. They are capable of bursts of speed but soon tire, and as a result mostly rely on ambush rather than the chase. Bears can stand on their hind feet and sit up straight with remarkable balance. Their front paws are flexible enough to grasp fruit and leaves. Bears' non-retractable claws are used for digging, climbing, tearing, and catching prey. The claws on the front feet are larger than those on the back and may be a hindrance when climbing trees; black bears are the most arboreal of the bears, and have the shortest claws. Pandas are unique in having a bony extension on the wrist of the front feet which acts as a thumb, and is used for grippingbambooshoots as the animals feed.[47]

Most mammals haveagoutihair, with each individual hair shaft having bands of color corresponding to two different types ofmelaninpigment. Bears however have a single type of melanin and the hairs have a single color throughout their length, apart from the tip which is sometimes a different shade. The coat consists of long guard hairs, which form a protective shaggy covering, and short dense hairs which form an insulating layer trapping air close to the skin. The shaggy coat helps maintain body heat during winter hibernation and is shed in the spring leaving a shorter summer coat. Polar bears have hollow, translucent guard hairs which gain heat from the sun and conduct it to the dark-colored skin below. They have a thick layer of blubber for extra insulation, and the soles of their feet have a dense pad of fur.[47]While bears tend to be uniform in color, some species may have markings on the chest or face and the giant panda has a bold black-and-white pelage.[50]

Bears have small rounded ears so as to minimize heat loss, but neither their hearing or sight are particularly acute. Unlike many other carnivorans they havecolor vision,perhaps to help them distinguish ripe nuts and fruits. They are unique among carnivorans in not having touch-sensitivewhiskerson the muzzle; however, they have an excellentsense of smell,better than that of the dog, or possibly any other mammal. They use smell for signalling to each other (either to warn off rivals or detect mates) and for finding food. Smell is the principal sense used by bears to locate most of their food, and they have excellent memories which helps them to relocate places where they have found food before.[47]

Brown bear skull

Theskullsof bears are massive, providing anchorage for the powerfulmasseterandtemporaljaw muscles. Thecanine teethare large but mostly used for display, and themolarteeth flat and crushing. Unlike most other members of the Carnivora, bears have relatively undevelopedcarnassialteeth, and their teeth are adapted for a diet that includes a significant amount of vegetable matter.[47]Considerable variation occurs indental formulaeven within a given species. This may indicate bears are still in the process of evolving from a mainly meat-eating diet to a predominantly herbivorous one. Polar bears appear to have secondarily re-evolved carnassial-like cheek teeth, as their diets have switched back towards carnivory.[51]Sloth bears lack lower central incisors and use their protrusible lips for sucking up the termites on which they feed.[47]The general dental formula for living bears is:3.1.2–4.23.1.2–4.3.[47]The structure of thelarynxof bears appears to be the mostbasalof the caniforms.[52]They possess air pouches connected to thepharynxwhich mayamplifytheir vocalizations.[53]

Bears have a fairly simple digestive system typical for carnivorans, with a single stomach, short undifferentiated intestines and nocecum.[54][55]Even the herbivorous giant panda still has the digestive system of a carnivore, as well as carnivore-specific genes. Its ability to digestcelluloseis ascribed to the microbes in its gut.[56]Bears must spend much of their time feeding in order to gain enough nutrition from foliage. The panda, in particular, spends 12–15 hours a day feeding.[57]

Distribution and habitat

Thespectacled bearis the only species found in South America.[58]
Further information:List of carnivorans by population

Extant bears are found in sixty countries primarily in the Northern Hemisphere and are concentrated in Asia, North America, and Europe. An exception is thespectacled bear;native to South America, it inhabits theAndean region.[58]Thesun bear's range extends below the equator in Southeast Asia.[59]TheAtlas bear,a subspecies of the brown bear was distributed in North Africa from Morocco to Libya, but it became extinct around the 1870s.[60]

The most widespread species is thebrown bear,which occurs from Western Europe eastwards through Asia to the western areas of North America. TheAmerican black bearis restricted to North America, and thepolar bearis restricted to the Arctic Ocean. All the remaining species of bear are Asian.[58]They occur in a range of habitats which include tropical lowland rainforest, both coniferous and broadleaf forests, prairies, steppes, montane grassland, alpine scree slopes, Arctic tundra and in the case of the polar bear,ice floes.[58][61]Bears may dig their dens in hillsides or use caves, hollow logs and dense vegetation for shelter.[61]

Behavior and ecology

American black beartracks atSuperior National Forest,Minnesota,U.S.

Brown and American black bears are generallydiurnal,meaning that they are active for the most part during the day, though they may forage substantially by night.[62]Other species may benocturnal,active at night, though female sloth bears with cubs may feed more at daytime to avoid competition from conspecifics and nocturnal predators.[63]Bears are overwhelmingly solitary and are considered to be the most asocial of all the Carnivora. The only times bears are encountered in groups are mothers with young or occasional seasonal bounties of rich food (such as salmon runs).[64][65]Fights between males can occur and older individuals may have extensivescarring,which suggests that maintainingdominancecan be intense.[66]With their acute sense of smell, bears can locate carcasses from several kilometres away. They useolfactionto locate other foods, encounter mates, avoid rivals and recognize their cubs.[47]

Feeding

Giant pandafeeding onbambooatSmithsonian National Zoological Park,Washington, D. C.This species is almost entirelyherbivorous.

Most bears are opportunisticomnivoresand consume more plant than animal matter, and appear to have evolved from an ancestor which was a low-protein macronutrient omnivore.[67]They eat anything from leaves, roots, andberriestoinsects,carrion,fresh meat, and fish, and have digestive systems and teeth adapted to such a diet.[58]At the extremes are the almost entirely herbivorous giant panda and the mostly carnivorous polar bear. However, all bears feed on any food source that becomes seasonally available.[57]For example, Asiatic black bears inTaiwanconsume large numbers ofacornswhen these are most common, and switch toungulatesat other times of the year.[68]

When foraging for plants, bears choose to eat them at the stage when they are at their most nutritious and digestible, typically avoiding oldergrasses,sedgesand leaves.[55][57]Hence, in more northern temperate areas, browsing and grazing is more common early in spring and later becomes more restricted.[69]Knowing when plants are ripe for eating is a learned behavior.[57]Berries may be foraged in bushes or at the tops of trees, and bears try to maximize the number of berries consumed versus foliage.[69]In autumn, some bear species forage large amounts of naturallyfermentedfruits, which affects their behavior.[70]Smaller bears climb trees to obtainmast(edible reproductive parts, such as acorns).[71]Such masts can be very important to the diets of these species, and mast failures may result in long-range movements by bears looking for alternative food sources.[72]Brown bears, with their powerful digging abilities, commonly eat roots.[69]The panda's diet is over 99% bamboo,[73]of 30 different species. Its strong jaws are adapted for crushing the tough stems of these plants, though they prefer to eat the more nutritious leaves.[74][75]Bromeliadscan make up to 50% of the diet of the spectacled bear, which also has strong jaws to bite them open.[76]

Polar bear feeding on a seal on an ice floe north ofSvalbard,Norway. It is the most carnivorous species.

The sloth bear is not as specialized as polar bears and the panda, has lost several front teeth usually seen in bears, and developed a long, suctioning tongue to feed on theants,termites,and other burrowing insects. At certain times of the year, these insects can make up 90% of their diets.[77]Some individuals become addicted to sweets in garbage inside towns where tourism-related waste is generated throughout the year.[78]Some species may raid the nests ofwaspsandbeesfor thehoneyand immature insects, in spite of stinging from the adults.[79]Sun bears use their long tongues to lick up both insects and honey.[80]Fish are an important source of food for some species, and brown bears in particular gather in large numbers atsalmon runs.Typically, a bear plunges into the water and seizes a fish with its jaws or front paws. The preferred parts to eat are the brain and eggs. Small burrowing mammals likerodentsmay be dug out and eaten.[81][69]

The brown bear and both species of black bears sometimes take large ungulates, such asdeerandbovids,mostly the young and weak.[68][82][81]These animals may be taken by a short rush and ambush, though hiding young may be sniffed out and pounced on.[69][83]The polar bear mainly preys on seals, stalking them from the ice or breaking into their dens. They primarily eat the highly digestible blubber.[84][81]Large mammalian prey is typically killed with raw strength, including bites and paw swipes, and bears do not display the specialized killing methods of felids and canids.[85]Predatory behavior in bears is typically taught to the young by the mother.[81]

Bears are prolificscavengersandkleptoparasites,stealing foodcachesfrom rodents, and carcasses from other predators.[55][86]For hibernating species, weight gain is important as it provides nourishment during winter dormancy. A brown bear can eat 41 kg (90 lb) of food and gain 2–3 kg (4.4–6.6 lb) of fat a day prior to entering its den.[87]

Communication

CaptiveAsian black bearsduring an aggressive encounter

Bears produce a number of vocal and non-vocal sounds. Tongue-clicking, grunting or chuffing many be made in cordial situations, such as between mothers and cubs or courting couples, while moaning, huffing, snorting or blowing air is made when an individual is stressed. Barking is produced during times of alarm, excitement or to give away the animal's position. Warning sounds include jaw-clicking and lip-popping, while teeth-chatters,bellows,growls,roarsand pulsing sounds are made in aggressive encounters. Cubs may squeal, bawl, bleat or scream when in distress and make motor-like humming when comfortable or nursing.[52][88][89][90][91][92]

Sloth bearrubbing against a tree atNagarhole Tiger Reserve,India

Bears sometimes communicate with visual displays such asstanding upright,which exaggerates the individual's size. The chest markings of some species may add to this intimidating display. Staring is an aggressive act and the facial markings of spectacled bears and giant pandas may help draw attention to the eyes duringagonisticencounters.[50]Individuals may approach each other by stiff-legged walking with the head lowered. Dominance between bears is asserted by making a frontal orientation, showing thecanine teeth,muzzle twisting and neck stretching. A subordinate may respond with a lateral orientation, by turning away and dropping the head and by sitting or lying down.[65][93]

Bears also communicate with their scent byurinatingon[94]orrubbingagainst trees and other objects.[95]This is usually accompanied by clawing and biting the object. Bark may be spread around to draw attention to the marking post.[96]Pandas establish territories by marking objects with urine and a waxy substance from their anal glands.[97]Polar bears leave behind their scent in their tracks which allow individuals to keep track of one another in the vast Arctic wilderness.[98]

Reproduction and development

American black bears mating at theNorth American Bear Center

The mating system of bears has variously been described as a form ofpolygyny,promiscuityandserial monogamy.[99][100][101]During the breeding season, males take notice of females in their vicinity and females become more tolerant of males. A male bear may visit a female continuously over a period of several days or weeks, depending on the species, to test her reproductive state. During this time period, males try to prevent rivals from interacting with their mate. Courtship may be brief, although in some Asian species, courting pairs may engage in wrestling, hugging, mock fighting and vocalizing.Ovulation is induced by mating,which can last up to 30 minutes depending on the species.[100]

Polar bearmother nursing her cub

Gestationtypically lasts 6–9 months, includingdelayed implantation,and litter size numbers up to four cubs.[102]Giant pandas may give birth to twins but they can only suckle one young and the other is left to die.[103]In northern living species, birth takes place during winter dormancy. Cubs are born blind and helpless with at most a thin layer of hair, relying on their mother for warmth. The milk of the female bear is rich in fat and antibodies and cubs may suckle for up to a year after they are born. By 2–3 months, cubs can follow their mother outside the den. They usually follow her on foot, but sloth bear cubs may ride on their mother's back.[102][61]Male bears play no role in raising young.Infanticide,where an adult male kills the cubs of another, has been recorded in polar bears, brown bears and American black bears but not in other species.[104]Males kill young to bring the female intoestrus.[105]Cubs may flee and the mother defends them even at the cost of her life.[106][107][108]

In some species, offspring may become independent around the next spring, though some may stay until the female successfully mates again. Bears reachsexual maturityshortly after they disperse; at around 3–6 years depending on the species. Male Alaskan brown bears and polar bears may continue to grow until they are 11 years old.[102]Lifespan may also vary between species. The brown bear can live an average of 25 years.[109]

Hibernation

Main article:Hibernation

Bears of northern regions, including theAmerican black bearand thegrizzly bear,hibernate in the winter.[110][111]During hibernation, the bear's metabolism slows down, its body temperature decreases slightly, and its heart rate slows from a normal value of 55 to just 9 beats per minute.[112]Bears normally do not wake during their hibernation, and can go the entire period without eating, drinking, urinating, or defecating.[47]Afecal plugis formed in the colon, and is expelled when the bear wakes in the spring.[113]If they have stored enough body fat, their muscles remain in good condition, and their protein maintenance requirements are met from recycling wasteurea.[47]Female bears give birth during the hibernation period, and are roused when doing so.[111]

Mortality

Hunters with shot bear, Sweden, early 20th century. This photograph is in theNordic Museum.

Bears do not have many predators. The most important are humans, and as they started cultivating crops, they increasingly came in conflict with the bears that raided them. Since the invention of firearms, people have been able to kill bears with greater ease.[114]Felidslike thetigermay also prey on bears,[115][116]particularly cubs, which may also be threatened by canids.[14][101]

Bears are parasitized by eighty species of parasites, including single-celled protozoans and gastro-intestinal worms, and nematodes and flukes in their heart, liver, lungs and bloodstream. Externally they have ticks, fleas and lice. A study of American black bears found seventeen species of endoparasite including the protozoanSarcocystis,the parasitic wormDiphyllobothrium mansonoides,and the nematodesDirofilaria immitis,Capillaria aerophila,Physalopterasp.,Strongyloidessp. and others. Of these,D. mansonoidesand adultC. aerophilawere causing pathological symptoms.[117]By contrast, polar bears have few parasites; many parasitic species need a secondary, usually terrestrial, host, and the polar bear's life style is such that few alternative hosts exist in their environment. The protozoanToxoplasma gondiihas been found in polar bears, and the nematodeTrichinella nativacan cause a serious infection and decline in older polar bears.[118]Bears in North America are sometimes infected by aMorbillivirussimilar to thecanine distemper virus.[119]They are susceptible toinfectious canine hepatitis(CAV-1), with free-living black bears dying rapidly of encephalitis and hepatitis.[120]

Relationship with humans

Conservation

Main article:Bear conservation
Giant pandas at theSichuan Giant Panda Sanctuaries
A barrel trap inGrand Teton National Park,Wyoming,used to relocate bears away from where they mightattack humans.

In modern times, bears have come under pressure through encroachment on their habitats[121]and illegal trade in bear parts, including the Asianbile bearmarket, though hunting is now banned, largely replaced by farming.[122]TheIUCNlists six bear species asvulnerable;[123]even the twoleast concernspecies, the brown bear and the American black bear,[123]are at risk ofextirpationin certain areas. In general these two species inhabit remote areas with little interaction with humans, and the main non-natural causes of mortality are hunting, trapping, road-kill and depredation.[124]

Laws have been passed in many areas of the world to protect bears fromhabitat destruction.Public perception of bears is often positive, as people identify with bears due to their omnivorous diets, their ability to stand on two legs, and their symbolic importance.[125]Support for bear protection is widespread, at least in more affluent societies.[126]The giant panda has become a worldwide symbol of conservation. TheSichuan Giant Panda Sanctuaries,which are home to around 30% of the wild panda population, gained aUNESCO World Heritage Sitedesignation in 2006.[127]Where bears raid crops or attack livestock, they may come into conflict with humans.[128][129]In poorer rural regions, attitudes may be more shaped by the dangers posed by bears, and the economic costs they cause to farmers and ranchers.[128]

Attacks

Main article:Bear attack
Bear warning sign inAlberta,Canada

Several bear species aredangerous to humans,especially in areas where they have become used to people; elsewhere, they generally avoid humans.Injuries caused by bearsare rare, but are widely reported.[130]Bears may attack humans in response to being startled, in defense of young or food, or even for predatory reasons.[131]

Entertainment, hunting, food and folk medicine

Bears in captivity have for centuries been used for entertainment. They have been trained todance,[132]and were kept forbaitingin Europe from at least the 16th century. There were five bear-baiting gardens inSouthwark,London, at that time; archaeological remains of three of these have survived.[133]Across Europe,nomadicRomanibear handlers calledUrsarilived by busking with their bears from the 12th century.[134]

Bears have been huntedfor sport, food, andfolk medicine.Their meat is dark and stringy, like a tough cut of beef. InCantonese cuisine,bear paws are considered a delicacy. Bear meat should be cooked thoroughly, as it can be infected with the parasiteTrichinella spiralis.[135][136]

The peoples of eastern Asia use bears' body parts and secretions (notably their gallbladders and bile) as part oftraditional Chinese medicine.More than 12,000 bears are thought to be kept on farms in China, Vietnam, and South Korea for the production of bile. Trade in bear products is prohibited underCITES,but bear bile has been detected in shampoos, wine and herbal medicines sold in Canada, the United States and Australia.[137]

Cultural depictions

Main article:Cultural depictions of bears
See also:Bear in heraldry

Bears have been popular subjects in art, literature, folklore and mythology. The image of the mother bear was prevalent throughout societies in North America and Eurasia, based on the female's devotion and protection of her cubs.[138]In manyNative Americancultures, the bear is a symbol of rebirth because of its hibernation and re-emergence.[139]A widespread belief among cultures of North America and northern Asia associated bears withshaman;this may be based on the solitary nature of both. Bears have thus been thought to predict the future and shaman were believed to have been capable of transforming into bears.[140]

There is evidence of prehistoricbear worship,though this is disputed by archaeologists.[141]It is possible that bear worship existed in early Chinese andAinu cultures.[142]The prehistoricFinns,[143]Siberian peoples[144]and more recentlyKoreansconsidered the bear as the spirit of their forefathers.[145]Artio(Dea Artioin theGallo-Roman religion) was aCelticbear goddess. Evidence of her worship has notably been found atBern,itself named for the bear. Her name is derived from the Celtic word for "bear",artos.[146]Inancient Greece,the archaic cult ofArtemisin bear form survived into Classical times atBrauron,where young Athenian girls passed an initiation rite asarktoi"she bears".[147]

The constellations of Ursa Major andUrsa Minor,the great and little bears, are named for their supposed resemblance to bears, from the time ofPtolemy.[b][8]The nearby starArcturusmeans "guardian of the bear", as if it were watching the two constellations.[149]Ursa Major has been associated with a bear for as much as 13,000 years sincePaleolithictimes, in the widespreadCosmic Huntmyths. These are found on both sides of theBering land bridge,which was lost to the sea some 11,000 years ago.[150]

Bears are popular in children's stories, includingWinnie the Pooh,[151]Paddington Bear,[152]Gentle Ben[153]and "The Brown Bear of Norway".[154]An early version of "Goldilocks and the Three Bears",[155]was published as "The Three Bears" in 1837 byRobert Southey,many times retold, and illustrated in 1918 byArthur Rackham.[156]TheHanna-BarberacharacterYogi Bearhas appeared in numerous comic books,animated television showsand films.[157][158]TheCare Bearsbegan as greeting cards in 1982, and were featured as toys, on clothing and in film.[159]Around the world, many children—and some adults—haveteddy bears,stuffed toysin the form of bears, named after the American statesmanTheodore Rooseveltwhen in 1902 he had refused to shoot an American black bear tied to a tree.[160]

Bears, like other animals, may symbolize nations. TheRussian Bearhas been a commonnational personificationfor Russia from the 16th century onward.[161]Smokey Bearhas become a part of American culture since his introduction in 1944, with his message "Only you can prevent forest fires".[162]

Organizations

Juvenile pandas at theChengduResearch Base of Giant Panda Breeding

The International Association for Bear Research & Management, also known as theInternational Bear Association,and theBear Specialist Groupof the Species Survival Commission, a part of theInternational Union for Conservation of Naturefocus on the natural history, management, and conservation of bears. Bear Trust International works for wild bears and other wildlife through four core program initiatives, namely Conservation Education, Wild Bear Research, Wild Bear Management, and Habitat Conservation.[163]

Specialty organizations for each of the eight species of bears worldwide include:

  • Vital Ground, for the brown bear[164]
  • Moon Bears, for the Asiatic black bear[165]
  • Black Bear Conservation Coalition, for the North American black bear[166]
  • Polar Bears International, for the polar bear[167]
  • Bornean Sun Bear Conservation Centre, for the sun bear[168]
  • Wildlife SOS, for the sloth bear[169]
  • Andean Bear Conservation Project, for the Andean bear[170]
  • Chengdu Research Base of Giant Panda Breeding, for the giant panda[171]

See also

Notes

  1. ^Treatingpinnipeds[41]asmarine mammals.
  2. ^Ptolemy named the constellations in Greek:Ἄρκτος μεγάλη(Arktos Megale) andἌρκτος μικρά(Arktos Mikra), the great and little bears.[148]

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General and cited references

Further reading

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