|
|
The Modern Archetypal Bear
In terms of basic features, bears have heavily built bodies with relatively short legs, necks and tails. They have rounded ears and noticeably small eyes relative to their large body size.
While all bears are quite large, there is a great deal of difference with some adults weighing around 50 kilograms (110 pounds) while others tip the scales at over 1000 kilograms (2200 pounds).
Bears have heavy fur coats which they shed each year. Bears carry thick layers of subcutaneous fat under their skin.
Most bears are very agile and swift creatures. Large brown bears are capable of outrunning a horse at a speed of 55 to 65 kilometers per hour (35 to 40 miles per hour). All bears are capable swimmers and nearly all bears can climb with considerable skill, speed and dexterity.
Unlike most carnivores, the lips of bears are not attached to the gums. This allows them to be very mobile and protrusible.
The foot of a bear has five toes equipped with curved non-retractable claws. The claws on the hind feet are longer than on the forefeet. Bears walk in what is called a plantigrade manner as do humans. This means that the heel and foot are placed flat on the ground when a bear walks. This stance accounts for the ability bears demonstrate to balance on their hind legs. When observing bears walking, it is also noticeable that the front feet are placed on the ground in an inward (toed-in) position.
The teeth of modern bears have changed significantly from their predecessors. They have retained the canine teeth useful for catching and killing prey. However, their premolars, the carnassials, once shaped to facilitate the shearing of meat into smaller, swallowable chunks have become the heavy crushing type typical of plant eaters. With more than 75% of the diets of most bears being plant material, this evolutionary change has clearly been important to the survival of present day bears.
Bear teeth grow slowly throughout the entire life span of the animal. In a manner similar to the growth rings of trees, tiny growth rings called cementum annuli are formed each year of the bear's life. Extraction of a tiny premolar is often used by current bear researchers to determine the age of a captured bear.
In the wild, bears older than thirty years are very rare exceptions, if ever. The presence of older bears within a geographic area is a positive sign of limited habit encroachment, trapping, hunting, poaching and other mortality factors.
In many areas, older bears are very rare with few adult bears older than ten to twelve years. This trend is cause for real concern when evaluating the long term viability of an existing bear population within a specific geographic area.
As with all wild animals, bears are susceptible to a variety of parasites and illnesses. Over fifty kinds of internal and external parasites have been documented in or on bears.
Some of the internal parasites include protozoa, intestinal flukes, tapeworms, hookworms, and roundworms. One variety, called Trichinella, is responsible for the seriously debilitating illness called trichinosis which can affect humans who eat raw or under-cooked bear meat. It appears that bears from the arctic and taiga forests are particularly susceptible. It is estimated that nearly all polar bears and 75% of brown bears are affected with the Trichinella parasite.
Bears also appear to suffer from many of the illnesses of modern man, including arthritis, tuberculosis, bronchopneumonia and others. Poor dental health caused by broken, injured or overly worn teeth can also seriously affect the overall health of any bear.
Bears are also susceptible to the ingestion of inert materials such as plastics which are incidentally in the environment or placed in unsecured garbage dumps and landfill sites.
Most bear species have excellent eyesight. As carnivores, their eyes are set relatively close together and face forward. This provides them with excellent depth perception and with the ability to track moving prey. Researchers have observed that bears are capable of detecting very small movements from several hundred yards away.
Bears have some form of colour vision or at least the ability to respond to different colour shadings. Also, the fact that bears are able to forage both during daylight and at night is another sign of good functional eyesight. Bears also demonstrate excellent hearing.
Their keen sense of smell is legendary and is often said to be comparable to that of a bloodhound. Because it is so good, bears will often rise to a standing position or move to a higher elevation to better "sniff the air". While initial observations of this behaviour were used to postulate poor eyesight in bears, it now appears that, as an extremely successful survival mechanism, bears prefer whenever possible to use all three of their highly developed sensory modalities - namely smell, eyesight and hearing.
Humankind does not have, at present, an understanding of how to measure bear intelligence. With certainty, however, we can ascribe the words "very curious" to describe bears. This curiosity extends far beyond the search for food. Rather, it appears to apply to virtually any new object or event within their environment.
Also, bears appear to have the capacity for learning. Thus, if a bear cub travelling with its mother happens upon a particularly rich food source, it will return to the same site on a repeated basis, even without its mother.
Bears are also known to strategically place themselves in locations which allow them to watch a passing human while remaining completely hidden. Some researchers believe this self-concealment suggests conscious thought and therefore some level of self-awareness.
Numerous examples are also recorded of a bear, who is being pursued by a human, modifying its path to avoid leaving tracks. Similarly, bears have been observed using sophisticated strategies to either avoid or deliberately set off the trigger mechanism of a live trap.
Bears, particularly in northern climates, must gain maximal weight during the pre-winter period in order to survive hibernation. In the case of females, sufficient body mass is necessary if she is going to successfully birth and nurture one or more developing cubs.
During late summer when mast (i.e., nut) crops are mature, bears have been known to consume up to 20,000 calories per day. This would be equivalent to a human eating forty hamburgs finished off with forty sundae desserts in a one day period.
Over time, individual bears learn to selectively travel to a number of small areas to take advantage of seasonal food sources. The routes between these areas are often referred to as travel lanes or corridors.
Bears have consistently demonstrated an strong homing instinct. There are many recorded examples of transplanted "nuisance or garbage" bears returning to their home range from a distance of over 160 kilometers (100 miles). In some cases, bears have demonstrated incredible tenacity in overcoming many physical barriers, including large bodies of water, to return to their home range.
For animals, hibernation represents a successful survival strategy where cold weather conditions combined with a limited food supply threaten the survival of the species. Bears in relatively mild climates may not hibernate or hibernate only for short periods in relatively open, uninsulated locations.
Where inhospitable climates occur for a significant portion of the year, bears will choose to enter a low cave, a hollow tree, a dense bush pile or dig an earthen den which they then line with dried grasses and leaves to provide an insulated bed.
As mentioned earlier under Food Strategies, high protein food sources are sought after as bears strive to put on sufficient fat resources necessary for the bear to survive the hibernation process. During the period of hibernation which can last for anywhere from two to seven and a half months depending on the severity of the climate, bears will neither eat, drink, urinate or defecate.
Bears enter a state of hibernation which is somewhat different than for smaller mammals such as chipmunks, marmots, etc. For smaller mammals, their body temperature drops quite low causing them to enter a deep sleep from which they are not easily aroused. On the other hand, a hibernating bear's body temperature only drops approximately 5 degrees centigrade (9 degrees Fahrenheit) from its normal 31 to 37.4 degrees centigrade (87.8 degrees to 99 degrees Fahrenheit). This means bears can be awakened quite easily.
Other bodily organs change their functioning in significant ways. The heart rate of a hibernating bear drops from 40 to 50 bears per minute during a normal sleeping cycle to just 8 to 10 beats per minute. Oxygen consumption is also halved and the caloric requirements are reduced significantly. Their unique metabolic system constantly stabilizes all life processes including the ability to recycle nitrogen thereby preventing toxic uremia which would be fatal to the bear.
On emerging from hibernation, bears are very lethargic for several weeks. This slowness gradually lessens as their metabolic system returns to pre-hibernation levels.
Adult bears come together as mating pairs for two to three weeks during the annual breeding season. The males are attracted to the female by the distinctive scent she gives off as she enters estrus, the time when she is ready to conceive.
Bears mate in a manner similar to wolves, coyotes and dogs. The male mounts from the rear with the male often clasping his forelimbs around the female's waist to maintain his balance and hold her in position. The length of copulation may vary from one to twenty minutes with both species and individual variability being present. After a period of repeated copulations, the female and male separate and return to their solitary lifestyles.
Bears from warmer climates who do not hibernate give birth at any time of the year. However, for bears from moderate to severe climates, the birth of young takes place during hibernation. Although mating usually occurs in the late spring or early summer, the blastocyst, the name given to the little ball of cells resulting from the growth of the fertilized ovum, simply free floats in the female reproductive tract for up to five months. Sometime in October or November, as denning is occurring, delayed implantation occurs with the blastocyst finally attaching itself to the uterine wall.
As with a number of other animals, including mink, kangaroo and red deer, implantation of the fertilized egg will only occur if the female's health and nutritional well-being as determined by her fat reserves are beyond a threshold level needed for survival.
After successful implantation, a relatively short gestation ranging from six to eight weeks results in remarkably small, newborn cubs. For example, newborn brown bears, at 280 grams (10 ounces), weigh approximately 1/720th as much as their mother.
The tiny cubs are blind when born and look almost naked with only a covering of very fine hair. They will nurse as their hibernating mother sleeps, always remaining close to their mother to benefit from her warmth and the sustenance-providing nipples to which they are immediately drawn at birth.
Prior to their entrance from the den, the cubs eyes will have opened and they will have experienced significant weight gains. They will also be covered with a thick covering of warm, insulating fur.
The female invariably raises her young alone. Bears are very protective mothers. The female is very willing to fight in defense of her cubs. Adult males often present the greatest danger to young bears. Since females do not come into estrus while they have young cubs at their side (up to two to three years of age), it has been postulated by researchers that there is a possible biological drive in adult males to kill young cubs in order to allow the female to come into estrus sooner.
Previous beliefs whereby bears were seen living in isolation with the exception of the mating season has now given way to new understandings of the importance of the family unit as a basic construct of understanding bears and their behaviour.
Young bears usually spend the first two to three years of life at the side of their mother and in the company of one or more siblings. With females coming into estrus, mating, conceiving and giving birth and then raising cubs in a repeating cycle, females live the majority of their lives within a family unit.
We have also come to learn that even after being weaned and separated from their mother, siblings may live, feed and travel together for a number of years before separating.
As mentioned in the Reproductive Behaviour section, adult bears, usually as a mating pair, may live together for two to three weeks during the breeding season. Also, abundant food sources such as large carcasses, fish-spawning streams or uncontrolled garbage dumps existing within a confined geographic area may result in bears living and feeding in close proximity for periods of time.
Also, environmental conditions may result in concentrations of bears within a geographic region. Each fall, polar bears gather along the northern coast of Hudson Bay waiting for "freeze-up" so that they can move to their winter feeding grounds out on the ice.
A dominance hierarchy is a survival mechanism designed to prevent violent encounters that could lead to serious injury of one or both animals of the same species. In bears, dominance is usually a matter of size and sex. Males are dominant over females, except females with cubs. With cubs at her side, a female will, if necessary, fight to the death with a normally dominant male.
When two bears of relatively close dominance meet or contest a favoured habitat location or food source, ritualized threat displays or possibly even short fights may occur before one of the animals gives way to the dominance of the other. The less dominant bear will normally acknowledge their position by physically moving away or sitting a sufficient distance away as to not disturb the more dominant bear.
After a dominance hierarchy has been established, the order is usually maintained solely by posturing and head movements. A loud roar or "mouthing" - the waving of an open mouth towards another bear who has come too close often serves to alert the less dominant bear that it should retreat or make a wider circle as it moves from one location to another within a communal feeding situation.
"The Bear Den" Home Page
The Evolution of Bears
The Modern Archetypal Bear (back to the top of this
page)
Brown and Grizzly Bears
American Black Bears
Polar Bears
Giant Panda Bears
Asiatic Black Bears
Spectacled Bears
Sloth Bears
Sun Bears
The Bear Den News
Bear Conservancy Organizations
The Bear Den Book Shelf
The Bear Den Video Guide
The Bear Den In-Depth Reviews
The Bear Den Photo Gallery
The Bear Den Quotable Quotes
The Bear Den Guide to Backcountry
Wisdom
Wildlife, Conservancy and
Backcountry Web Sites
The Bear Den Comments from Visitors
Would You Like to learn ABOUT exotic PETS?
ABOUT knows more ABOUT Exotic Pets