BEARS; THEIR CHARACTERISTICS, EATING AND BREEDING BEHAVIOR AND HIBERNATION

BEARS

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Asiatic black bear
Southeast Asia and East Asia are home to three bear species: 1) the sloth bear of the Indian subcontinent; 2) sun bears (also known as Malayan bears) of southern Asia; and 3) moon bears (also known as Asiatic black bears) bears of Asia. Relatively little is known about these bears. There are also brown bears in the Himalayas, northern China, Mongolia, Japan and Russia. See Northern Asian Animals. [Sources: Wikipedia, Bears of the World by Terry Domico and Mark Newman (Facts on File, 1988) and articles from National Geographic, Smithsonian magazine and the New York Times]

Bears are the world's largest carnivore (polar bears and brown bears are bigger than Siberian tigers and lions, the next largest carnivores). But that is technically correct as most bears are omnivores that get most of the nutrients from berries, leaves, roots, and other kinds of vegetation, and are only partly carnivorous.

The are only eight kinds of bears: In addition to the ones named above the others are: 1) polar bears of the Arctic (which evolved from brown bears a couple million years ago; 2) brown bears of North America, Asia and Europe (Grizzlies and Kodiak bears are kinds of brown bears; 3) black bears of North America; and 4) Speckled bear of South America. 5) Pandas. Whether or not pandas are bears is a matter of debate but these days most scientists do regard them as bears. There are no bears in Australia or Africa.

Bears belong to the Carnivora order, Ursidae family and Ursus genus. Males are known as boars and females are called sows and young are called cubs. A group of bears is called a "sloth." You don’t see groups very often. There are around 700,000 black bears and 70,000 brown bears and grizzly bears in North America. DNA studies have show that some brown bears are more closely related to polar bears than they are to other brown bears.

Many of the countries where Asian bears live are too poor to carry out studies or conduct conservation efforts. This is one reason why little is known about them and their populations are threatened by human activities. The governments of countries inhabited by these bears are sometimes assisted by the International Union for Conservation of Nature (IUCN), the World Wildlife Fund and other groups in their conservation efforts.

Book: Bears: Majestic Creatures of the Wild edited by Ian Stirlin (Rodale Press).

Bear Characteristics

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As a group bears look a lot alike. They vary in size and color but have the same general shape. The shapes and features of members of the cat family, for example, are much more varied. Bears are stockily built and have relatively short legs, necks and tails. They have rounded ears, strong curved claws and unusually small eyes for such large animals. Their teeth are large and pointed but not particularly useful for eating meat as they have lost their shearing ability. In contrast their molars are heavy and thick, ideal for crushing plant material. Bear teeth grown continually through the animal’s life and tiny growth rings are created every year, allowing scientists to use them to determine a bear’s age.

Bears walk on the heels of their feet like humans and move both legs on each side of their body at the same time when they walk which gives them and ambling, rolling gait. They can also move quite fast for such bulky-looking animals. If necessary brown bears can run short distances between 35mph and 40mph.

Bears can stand on their hind legs and strike out with their front claws. When they stand its often to look around and sniff the air. Their claws are nonretractable. Even so bears are quite adept at manipulating objects with their front feet. Most bears are good tree climbers and descent swimmers but are unable even to make even a small jump.

Most bears have a thick hid and thick, which keeps them warm in cold weather and protects them from insects in warm and hot weather. At least 55 kinds of internal and external parasites are known to infest beats. They include fleas, ticks, tapeworms, hookworms and roundworms. Bears suffer from many of the same maladies that humans do including arthritis, hemorrhoids and teeth cavities.

Bear Senses and Navigation

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Bears have a fairly good sense of hearing and an extremely keen sense of smell, by some estimates, seven times stronger than a bloodhound. It said that polar bears can smell the presence of a seal or a sandwich from more than a kilometer away. Contrary to the popular myth, they have good eyesight. They are especially adept at detecting movement at long distances. They appear to have some color vision but are very short sighted. Evidence of good eyesight include the fact they are active during both day and night and zoo bears are good at catching food tossed to them from some distance away and also adept at distinguishing between food and non-food items such as rocks.

Bears can navigate over long distances. Brown that have been moved more than a hundred miles form their home territory are have been able to find their way back. There is some evidence that bears find their way back toby using the earth's magnetic fields. In a Michigan a black bear found its way home after being airlifted to a new location 251 kilometers away. In Alaska, a brown bear had to swim at least 15 kilometers from an island it was relocated to to reach its mainland home territory.

Bear Hibernation

Bears don't hibernate in the true sense of the word in that their temperature remains relatively normal and they can easily be roused from their sleep. The temperature of true hibernating animals---namely small mammals such as chipmunks or marmots--- drops much lower, sometimes to near zero, and they can not be easily roused. Bears go into a dormant state and have a significate drop in pulse rate (8 beats a minute as opposed to 40 0r 50 beats a minute when sleeping in the summer) and breathing rate but their body temperature (in the case of black bears) only drops from a normal of 100̊F or 101̊F to 88̊.

Hibernating bears hibernate from two to six months, even in warm climates where there is plentiful food supply. Some individuals of hibernating species don’t hibernate even when there is a lot of snow and food is in short supply. Hibernation seems to be triggered by low temperatures, shorter days and snow and coincides with the disappearance of high-quality food. During lare summer some bears eat over 20,000 calories a day to put on enough fat to last them through the winter. During the days before hibernation some species eat highly fibrous materials that act as anus plus during hibernation. If given sufficient food zoo bears don’t hibernate.

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Japan Brown bear
Bears consume no food or water and don’t urinate or defecate while hibernating (smaller mammals by contrast have to periodically wake up and eat and expel waster). The water content of the blood remains at a constant level . The small amount of water loss that occurs naturally is offset by the breakdown of fat reserves to secure moisture. Bears burn about 4,000 calories a day while hibernating. The sometimes shiver while hibernating to stay warm. After they wake up it takes several weeks for them to resume normal eating, presumably because it takes some time for the metabolism to resume to normal.

Bears emerge from their dens after the hibernation is over with no significant loss of muscle strength. Humans immobile for the same amount of time lose 90 percent of their muscle strength. Nitrogenous waste of hibernating bears is recycled through the bladder and reabsorbed and not excreted as urine. Their body reprocesses the urine and converts it to an amino acid that is necessary to keep the bear alive. Scientist are studying how bears do this as a way of helping people whose kidneys have failed.

Bones of hibernating bear don't lose calcium and become brittle. Scientist are studying this phenomena as way of treating older people with osteoporosis. Sleeping bears don't suffer from obesity even though they sometimes carry huge amounts of fat. They tolerate high levels of cholesterol without developing arteriosclerosis; burn about 4,000 calories a day, but limit the fuel to body fat while preserving protein reserves. Scientists are studying these processes to help burn victims (who often die of rapid protein depletion).

Dens of Hibernating Bears

Bears may hibernate in caves, hollows of trees or in a depression under some leaves but most often they hibernate in dens dug by themselves or some other animal. They often hibernate year after years in the same area, often in the same den. Sometimes the move to the dens to hibernate during snow storms so their tracks are covered up.

In the late autumn, bears become lethargic and then dig a den and hibernate. Most dens are dug well in advance of hibernating time. In the forest bears often dig their dens underneath trees, whose root system acts as a roof and line the dens with evergreen boughs. grasses and bark for warmth and perhaps comfort. Many dens are dug in slopes apparently to minimize the accumulation of water. Theee dens usually face north so they have a insulating cover of snow.

Many dens have a sleeping areas that are higher than the entrance so an igloo-like pocket of air is generated that keeps the bear warm. About one in fifteen black bears doen't bother to build a den. Sows even give birth in the open and she and her cubs sleep through the winter while the snow piles up on top of them.


Bear Behavior and Territory

Bears have a reputation for behaving in an unpredictable manner. Evidence does not bear this out. They usually follow strict rules based on size, sex, age and social rank. Even so individual bears have distinct personalties and behavior, with individuals acting in different ways in similar circumstances.

Stephen Herrero, professor emeritus of environmental science at the University of Calgary and a leading authority on bear attacks. told the New York Times that bears are "complex, intelligent and individualistic." Bear lovers Maureen Enns and Charles Russell believe they have emotions and can appreciate beauty. Evidence of their intelligence includes their curiosity, the fact they can be trained to do difficult circus stunts and their ability to remember the exact location of food sources months later and pull the meat from traps without getting caught. Wildlife biologist Bruce McLellan encountered a female black bear that repeatedly stole they baits but avoided getting caught in a trap by placing a large rock into, setting off the trigger mechanism.

Many bears are good tree climbers. Black bears have curved claws and climb trees to escape danger or find food (brown bears generally are too big to climb trees). They climb by hugging the tree with their forelegs and pulling themselves up. They go down in a similar fashion feet first (unlike cats that often descend head first). Some bears make beds on the ground during the spring and summer that consists of a trampled down area or a shallow pit dug in the ground.

Bears are largely solitary animals that cover large distances in search of food. Often the only time bears come together is when males and females breed and sows take care of their cubs. But polar bears often den in communities and brown bears sometimes hunt salmon in communities. Sometimes a group of bears will gather around a kill or grbage dump. In addition siblings often stay together, sometimes for several years, after they leave their mothers.

Black bears are highly territorial and live in a rigidly matriarchal society. The average territory for males is 16 kilometers across; for females, five kilometers across. Some a male and female ranges overlap and sometimes a bear will wander into the territory of another bear (if they are caught they are often challenged or chased away, sometimes there are serious fights).

Black bear mothers define their territory and then subdivide it and give portions of it to their daughters when they are 1½ years old. At when 2½ years of age, when they become independent, the daughters expand the territory (and their mothers give up some) and claim it as their own. Territories are defined by scent markings. Persistent scratching is a way of releasing scent.

Males are forced leave their mother's territory when are 2½ or 3½ years of age and establish their own new territory. Often they have to wander a hundred kilometers or more from their mother's territory and engage in fights with other bears to establish their own territories. They often end up in marginal territories with less abundant food supplies.

Bear Eating Habits


Bears spend much of their time feeding. They are mainly vegetarians and they eat a wide variety of things. They often live on a feast and starve diet, eating lots when is plentiful and nothing when it scarce. The chief limiting factor for bear populations is food supply.

Bears locate food by smell, sniffing with their long mobile snout. They seem to prefer some foods when they have maximum protein content---usually during preflowering or early flowering stages. According to the book Bears of the World: “A bear normally spends its time in a series of small areas where it can find food. Collectively, these areas make up its home range. It moves around within the range in order to take advantage of seasonal food sources. The routes to and from these areas are often called travel lanes.

Bears feed on berries, roots, bulbs, nuts, tubers, grasses, sedges (protein-rich plants), and leaves. But they can also be skilled hunters and opportunistic feeders who feed on fish, birds, mice, gophers, deer, and rodents and even insects (an important source of protein when meat is scarce). Some bears love cowberries. Other are fond of ants and honey. Animal protein sources include insects, fish and small mammals. Many bears scavenge dead animals. Bears in coastal areas often feed on walrus, seal and whale carcasses that wash ashore. Some black bears have been observed earing moose and deer scat.

When available bears will eat from garbage dumps. Contrary to popular myth, garbage-eating bears do not become dependent on dumps as a food source. While feeding on garbage they also continue to eat normal bear food like roots and berries. The main problem with garbage bears is that they became a nuisance to humans and are sometimes shot.

Bear Breeding and Sex


Bears have a slow reproductive rate. Females take four to six years to reach sexual maturity, raise one or two cubs and mate every other year because they usually spend two years of more with their cubs. At any given time only about a third of the available females breed. The others are mostly taking care of cubs. If the supply is reduced, say because of a drought, sometimes females do not reproduce.

The breeding season usually last from late May to mid July but the egg does not implant into the womb until the fall. Utilizing a process known as delayed implantation a fertilized egg can “free float” in the female’s uterus for up to five months before attaching to the uterus wall and beginning development. If the female is in poor condition or too thin the egg will not implant. Males and females tend to mate in the female's territory. After mating the males tend stay in neutral "buffer zones” between the territories of females. Whether departure from the females's territory is voluntary or enforced is not known.

Males and females are promiscuous. It is not unusual for males and females to mate with different partners each breeding season. On this subject bear researcher Lynn Rogers told Smithsonian, "By our standard, it's pretty sinful, but if a male stayed in the same territory with a female, he'd be competing for food, and that wouldn't be good for the little ones at all."

Most fights between bears are between males fighting over receptive females. Older males are particularly aggressive towards younger males. Many male bears have nasty scars from such fights. Most showdowns consist of short fights and ritualized threat displays in which the males size up each other and decide who is dominant without really going at it. The largest male often gets the female not because she necessarily prefers him but rather because he is most effective driving off male rivals.

Bears copulate like dogs, with the male grasping the female around her body with his forelimbs. Often the male bites into the female’s neck while mating. Mating takes one to 20 minutes depending on species and individuals. Sometimes bears will mate several times a day.

Bear Cubs

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The gestation period is 240 days for polar bears, 225 days for brown bear, 219 days for black bears. The actual development time of the embryo is actually quite short, ranging from six to to eight weeks. The long gestation times listed above include the delayed implantation period. Almost the entire cycle of gestation, birth and lactation takes place in the den when the bear is hibernating.

Because the embryo development time is short, newborn bears are very small when they are born, typically less than ten percent the size of usual ratios between newborns and mothers. Newborn brown bears can weigh as little as 1/720th as their mothers (230 grams for the infant compared to 200 kilograms for the mother).

Sows give birth to blind, nearly naked, mouse-size cubs in their dens in January or February. As the infants nurse they are kept warm by their mother’s body. The eyes of black bear cubs open at around 40 days. Those of polar bears open at around 10 days. Over time their fur grows and thickens. Most sows raise one or two cubs. Occasionally three are seen.

Most cubs stay with their mothers for three years, hibernating together in the same den in the winter. Until they are weaned, young cubs follow their mothers everywhere and are nourished on milk than is as much as 33 percent fat. Females will viciously defend their cubs. Adult males play no role in the cub rearing process. They sometimes attack, kill and eat cubs. One reason cubs stay so close to their mother is for protection from male bears. In some localities up to 40 percent of cubs are killed by other bears.

The attrition rate among young cubs is very high. Many never make to their second birthday. Many are swept up by rivers, die from hunger or are eaten by other bears. Body weight is a good indicator of whether a cub survive or not. American black bear females sometimes abandon a cub born alone. Scientists theorize they do this because they don’t want to waste their energy on a single cub, whose survival is not assured, and choose to wait for a multiple birth the next season.

Large Carnivores Help Ecosystems

In January 2014, AFP reported: “The gradual decline of large carnivores such as lions, wolves or pumas is threatening the Earth's ecosystems, scientists warned as they launched an appeal to protect such predators. More than 75 per cent of 31 large carnivore species are on the decline, and 17 of them now occupy less than half of their former ranges, says a study published in the American journal Science. [Source: AFP, January 10, 2014]

"Globally, we are losing large carnivores," wrote William Ripple, lead author of the study and a professor in the Department of Forest Ecosystems and Society at Oregon State University. "Many of them are endangered," Ripple wrote. "Their ranges are collapsing. Many of these animals are at risk of extinction, either locally or globally. And, ironically, they are vanishing just as we are learning about their important ecological effects."

“Ripple and his colleagues reviewed published scientific reports and focused on seven species that have been studied for their widespread ecological effects. They are African lions, leopards, Eurasian lynx, cougars, gray wolves, sea otters and dingoes. The different reports show that a decline in pumas and wolves in Yellowstone National Park led to an increase in animals that feed on tree leaves and bushes, such as deer and elk. This disrupts the growth of vegetation and shifts populations of birds and small mammals, the researchers said.

In Europe, fewer lynx have been tied to overpopulation of roe deer, red foxes and hares, while in Africa the disappearance of lions and leopards has coincided with a dramatic increase in the number of olive baboons, which threaten farm crops and livestock. In Alaska, a decline in sea otters through killer whale depredation has triggered a rise in sea urchins and loss of kelp beds.

"Nature is highly interconnected," said Ripple. "The work at Yellowstone and other places shows how one species affects another and another through different pathways." For instance, avoiding overpopulation of herbivores allows forest flora to develop more and sequester more carbon dioxide, the main green house gas responsible for global warming. But the authors of the study say it will be very hard to convince people to accept a large scale restoration of large carnivore populations. People are afraid of them and have fought them to protect their livestock and their communities, they said.

Studying Bears

Scientists identify individual bears based on size, markings, scars, misshapen ears and the like. They determine the age of bears by counting rings in their teeth. Like rings in trees, bears form rings every winter on the bonelike coverings on their teeth roots.

Bears that are studied are trapped or shot with tranquilizer darts (often a muscle reliant such as succinycloline chloride) are weighed, examined, tagged and sometimes given radio collars. Bears traps used by scientists are usually comprised of two oil drums welded together with one end closed off and the other end fixed with a trap door that closes when a bear enter it. These traps are often baited with beef or bacon.

Scientists track the movement and territories of animals with radio collars. They attach the collars after the animals have been trapped or subdued with tranquilizer darts. After some time the batteries in the collars wear out and have to be replaced and the animals have to be trapped, tranquilized and re-collared.

Each battery powered radio collar emits a distinctive signal that can be picked up with a directional antennae. Some scientists study radio-collared bears when they are hibernating. When the collars are replaced the bears are located at their dens, injected with a tranquilizer, weighed and examined. The collars are adjusted for size and outfit with new batteries.

Image Sources: Wikimedia Commons

Text Sources: National Geographic, Natural History magazine, Smithsonian magazine, Wikipedia, New York Times, Washington Post, Los Angeles Times, Times of London, The Guardian, Top Secret Animal Attack Files website, The New Yorker, Time, Newsweek, Reuters, AP, AFP, The Economist, BBC, and various books and other publications.

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© 2008 Jeffrey Hays

Last updated May 2016

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