The Brown Bear

Brown Bear Anatomy

 

The brown bear (Ursus arctos) is a large bear distributed across much of northern Eurasia and North America.
 

General Information on Brown Bears

 

The Brown Bear is the most variably sized of extant bear species. 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 1.4 to 2.8 m and a shoulder height of 70 to 153 cm. Males are invariably larger than females, typically weighing around 30% more in most races. The tail is relatively short, ranging from 6 to 22 cm in length.

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Young of the year typically weigh 2–27 kg, while yearlings typically weigh 9–37 kg.

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Generally speaking, brown bears weigh the least when they emerge from hibernation in the spring and then reach peak weights when preparing for hibernation in the fall (when they often gorge on large food stuffs)

 

Sub-Species of Brown Bear

There are sixteen recognized subspecies of brown bear:

• Eurasian Brown Bear

• Alaskan Brown Bear

• Kamchatka Brown Bear

• California Golden Bear (extinct)

• East Siberian Brown Bear

• Atlas Bear (extinct)

• Ursus arctos dalli

• Peninsular Brown Bear

• Grizzly Bear

• Himalayan Brown Bear

• Ussuri Brown Bear

• Kodiak Bear

• Mexican Grizzly Bear (extinct)

• Tibetan Blue Bear

• Ursus arctos sitkensis

• Ursus arctos stikeenensis

• Syrian Brown Bear

• Marsican Brown Bear

Skeleton and Muscles

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 and sometimes 7 to 10 centimetres 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. 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 climb trees as can both species of black bear. 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 long, with huge Kodiak bears having measured up to 46 cm along their rear foot.

 

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 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.

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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.

Fur

Brown bears have long, thick fur, with a moderately long mane at the back of the neck. In India, brown bears can be reddish with silver tips, while in China, brown bears are bicolored with a yellow-brown or whitish cape across the shoulders. North American grizzlies can be dark brown (almost black) to cream (almost white) or yellowish brown. Black hairs usually have white tips. The winter fur is very thick and long, especially in northern subspecies, and can reach 11 to 12 centimetres 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.

Behaviour (Social, Reproductive, Feeding)

Social

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Brown bears are mostly solitary, although they may gather in large numbers at major food sources (i.e. moth colonies, 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. Female bears with cubs rival adult males in aggression, and are more intolerant of other bears than single females. Young adolescent males tend to be least aggressive, and have been observed in nonagonistic 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.

 

Reproductive

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The mating season is from mid-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 4 and 8 years of age, 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.

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Males, however, take no part in raising their cubs – parenting is left entirely to the females.

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The average litter has one to four cubs, usually two. There have been cases of bears with as many as six cubs. There are records of females sometimes adopting stray cubs or even trading cubs when they emerge from hibernation. 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. 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 and have developed enough to follow her and begin to forage for solid food.

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Cubs remain with their mother from two to four years (exceptionally to 4 and a half 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. Cubs flee up a tree when they see a strange male bear, and the mother often successfully defends them, even though the male may be twice as heavy as her.

 

Feeding

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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.

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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 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. 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. Brown bears living near coastal regions will regularly eat crabs and 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.

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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.

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Beyond the regular predation of salmon, most brown bears are not particularly active predators. 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 regular include various deer species such as elk, red deer, axis deer, roe deer, fallow deer, mule deer, moose and caribou. 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 in order to stun it enough to knock it over for consumption.

Communication

Bears produce a variety of vocalizations such as:

• Moaning: produced mostly as mild warnings to potential threats or in fear.

• Barking: produced during times of alarm, excitement or to give away the animal's position.

• Huffing: made during courtship or between mother and cubs to warn of danger.

• Growling: produced as strong warnings to potential threats or in anger.

• Roaring: used much for the same reasons as growls and also to proclaim territory and for intimidation.

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