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Both brown and grizzly bears are the same bear, Ursus arctos. There has been a tendency in North America to call the brown bear which lives in the interior, a grizzly, to distinguish it from the brown bears which live in coastal areas. The name "grizzly" comes from the silver tipped grizzled hairs that these brown bears develop as they get older.
The important thing is that whether someone calls it a brown bear or a grizzly bear, it is the same bear. It also does not matter whether it lives, in Asia, Europe or North America. We are always talking about the same bear!
The brown bear has the most widespread distribution throughout the world of any of the eight bear species (see map). They are found throughout most of the northern hemisphere including North America and Eurasia.
Their preferred habitat includes mountain forests, open meadows and large river valleys. Their range originally went from the northern arctic seacoasts, southward over the tundra-covered mountains of the north, throughout the boreal forests and as far south as Mexico on the North American continent and as far south as Spain, Italy and Iran in Eurasia. The southern limits of their range coincided with the end of travel corridors of preferred mountain forest habitat. There is also a population of brown bears on the Japanese island of Hokkaido.
It is estimated that there are currently somewhere between 125,000 and 150,000 brown bears throughout the world. In all but the most isolated and undeveloped habitat areas, brown bears have been eliminated from much of their possible range.
The coniferous forests of Eurasia (primarily located in the countries that comprised the former Soviet Union) are still believed to be a stronghold of the brown bear. It is estimated that approximately 100,000 brown bears still live in these areas.
In Spain, France and Italy, it is believed that there are still small isolated brown bear populations numbering a hundred or less bears.
In North America, the brown bear population has declined drastically. It is estimated that in the early 1800's there were approximately 100,000 brown bears. Today, there are between 40,000 and 50,000 brown bears. They have been virtually eliminated from the lower forty-eight states of the U.S. with less than 1,000 bears occupying less than 1% of their original range.
The remaining bears in North America are basically evenly distributed between the western provinces of Canada (particularly British Columbia Alberta, Yukon and the North West Territories) and Alaska.
The brown bear is a large mammal whose size and weight are extremely variable depending
on the availability of food, climatic conditions, etc.
In general, adult brown bears stand approximately 100 centimeters (3 1/2 feet) tall
when on all fours and have a approximate body length of just over 200 centimeters (6 1/2
to 7 feet).
The weight of brown bears is highly variable, normally ranging anywhere from 150 to 375
kilograms (330 to 825 pounds). Males within a geographic area may weigh more than twice as
much as females. As an indication of the variability among brown bears, male bears that
have access to the coastal areas often weigh 500 kilograms (1100 pounds) with some
individual animals weigh in excess of 680 kilograms (1500 pounds). This is twice as heavy
as the largest American male black bears.
The lifespan of brown bears in the wild can be 25 years or more.
Brown bears have a heavy stout body with strong muscular legs. They have a big head, short tail, small rounded ears, feet (i.e., both heel and toe make contact with the ground when walking in a manner similar to humans), and a hind foot with five toes. They are very quick such that they are able to attain speeds of 56 kilometers per hour (35 miles per hour) for a short distance.
Brown bears have a distinctive muscular shoulder hump and the claws on the front paws are large, strong and slightly curved. The front claws are approximately one and three-quarter times longer than the rear claws and generally visible even from a distance. The absolute length of the front claws are often 9 centimeters (3 inches) long with claws over 12 centimeters (4 3/4 inches) long not uncommon. Their claws are highly adapted to digging for food (eg., tubers, rodents, etc.) as opposed to climbing. The most common colour of the claws is brown.
While members of the order Carnivora , brown bears have evolved primarily into vegetarians with accompanying changes in their dental structure and digestive tract.
Brown bears are covered with a heavy shaggy fur. There are many colour phases including black, cinnamon, red, blond or a mixture of these colours.
Brown bears, like most wild creatures, seek foods which will return the highest nutritional value for the least expenditure of energy. Seasonal availability and geographic location are the biggest factors determining the primary food sources of brown bears.
Eating more than 200 types of plants, it has been determined that more than 75% of a brown bear's diet consists of vegetable matter including, berries, flowers, grasses and sedges, herbs, tubers, corms and roots, and nuts of all kinds. The importance of subsurface tubers, corms and roots to the brown bear's diet is demonstrated by the specialized development of their claws and shoulder musculature for digging.
For the remaining portion of their diet, animal matter such as decaying animal carcasses, fish, small marine animals, ants and other insects, honey, elk and moose calves and a variety of other small mammals (e.g., ground squirrels, marmots, etc.) are consumed.
Because of their large size, brown bears require a very high caloric intake of food. In order to achieve this, brown bears will eat 36 to 41 kilograms (80 to 90 pounds) of food per day during the summer to early fall peak feeding period if it is available to them. During this eating binge, brown bears are able to gain 1 1/4 to 2 3/4 kilograms (3 to 6 pounds) of fat each day.
A home range is the area an animal travels in its normal activities of gathering food, mating and caring for its young.
The size of the home range of an individual brown bear will vary with the concentration of high energy food sources. Thus, the more concentrated the food sources, the smaller the range necessary to maintain the animal. The size of the home range is extremely dynamic and varies from one geographic region to another and also from one year to another.
Researchers have shown that adult male brown bears living in the Brooks Range in Alaska have an average home range of approximately 1350 square kilometers (521 square miles). On the other hand, brown bears living in salmon-rich coastal areas require only about 27 square kilometers (10.5 square miles). The difference is access to adequate food resources.
In general, males have a home range which is four times to six times larger than females. The home range of a mature male bear will normally overlap the home range of at least two or three females and possibly many more.
Characteristically, a home range does not constitute one large area but rather is composed of many food source areas connected by travel lanes. The home range must also include rest areas and more remote areas for shelter, protection and denning.
Brown bears do not normally defend their home ranges from other bears and thus it is normal for the home ranges of individual bears to overlap each other.
Female brown bears normally become sexually mature in their fifth year with some waiting even later for their first mating. Copulation normally takes place in a manner similar to members of the canine (dog) family.
Mating normally occurs between late May and early July. Females will normally mate with a number of males over the approximate three weeks of the breeding season. Females will not come into estrus when they are nursing cubs.
Through a remarkable process referred to as delayed implantation, the fertilized ovum divides a few times and then floats free within the uterus for about six months with its development arrested. Sometime around the denning period, the embryo will attach itself to the uterine wall and after a period of eight weeks (January or February), the cubs will be born while the mother is still in hibernation.
Delayed implantation clearly serves an important survival need for the mother. Should she not have enough fat reserves to carry her through the winter, the embryo will not implant and it is simply reabsorbed by her body.
The number of cubs born normally ranges from one to four with two to three cubs being average. As a rule, the number of cubs a female will have increases as she gets older. Again, climate and food supply are important determinants of the size of the litter.
At birth, the cubs are blind, toothless, hairless and very tiny. They weigh 600 to 700 grams (21 to 25 ounces). This is roughly the size of a chipmunk. Virtually helpless, they are, however, able to move sufficiently to suckle on their mother who remains asleep. Her milk is calorically very rich containing over 20% fat. In contrast, human milk only contains about 4% fat.
Within the next several weeks, the cubs will develop rapidly on this rich diet such that they will be able to follow their mother when she leaves the den.
The survival of bear cubs is extremely tenuous. Up to 40% of brown bears cubs will die during their first year of life. Starvation, and disease will claim a number of cubs. Wolves, bobcats, eagles, mountain lions are also known to kill young cubs who become separated from their mother's side.
Infanticide is also a factor. Predation of cubs by adult male brown bears is also quite common. Three reasons have been postulated to account for infanticide: to provide food; to create a breeding opportunity for a male bear; and to reduce competition for common territory.
The cubs will normally stay with the mother for the first two and a half years. Occasionally, they will remain for an extra year. The cubs are generally weaned between July and September of their first year and stay with the mother through their first full two winters.
The survival of brown bear cubs is totally dependent on the skill of the mother in both protecting them and teaching them the basics of what to eat, where and how to get it, where to den, and how to cope with danger.
As adolescents, the young bears are still in extreme danger. Normally they are driven off by their mother as she prepares to breed once more. They must now become rapidly self sufficient if they are to stay alive and find sufficient food to build up their fat reserves to last over the long winter. Occasionally, young bears will spend a period of time together after they have been driven off by their mothers.
During late summer and early fall, all bears have, as a survival imperative, the need to gain as much weight as possible. Through the harvesting of available nut crops, fish, berries, etc., brown bears make very large weight gains. Such gains may be as much as 18 kilograms (40 pounds) per week. At such times, foraging may occur around the clock with only short rest periods.
The arrival of cold weather and/or snow precipitates the bear undergoing a remarkable metabolic transformation as it prepares for hibernation. Hibernation is an energy-saving process bears have developed to allow them to survive long periods when there is insufficient food available to maintain their body mass. As they stop eating and become increasingly lethargic, the bear will enter a rock cave; dig out a den; hole up in a dense brush pile, hollow log or tree cavity.
While hibernating, a bear's heart rate drops from between forty to seventy beats per minute to only eight to twelve beats per minute and its metabolism slows down by half. Unlike many other animals who hibernate, its body temperature only undergoes a minor reduction of 3 to 7 degrees Centigrade (5 to 9 degrees Fahrenheit).
During the entire period of hibernation, the brown bear will neither pass urea or solid fecal waste. While urea poisoning causing death would occur in all other animals within a week, bears have developed a unique process of recycling the urea into usable proteins.
Most brown bears vacate their winter dens over a one to two month period during April or May. Both the climatic conditions (snow cover and temperature) and physiological factors such as the bear's age, the status of its health and its remaining fat reserves affect the exact timing of emergence from its den. Normally, adult males emerge first. Females with newborn cubs are usually the last to leave their dens.
During the hibernation period, all bears lose a great deal of weight. Adult males and adolescent bears lose between 15% and 30% of their weight while it is not uncommon for a female with newborn cubs to lose as much as 40% of her weight.
The brown bear will be lethargic during its initial emergence from the den. It then resumes its normal foraging pattern as it completes the cycle of life.
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