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Metairie, LA USA
Local: 504-832-1663
Fax: 504-835-8692
Email: john@nature-images.com
About the Bears
Geographic Range
Palearctic, Nearctic, Oriental, Ethiopian: Ursus arctos once ranged throughout northern and central Europe, Asia, the Atlas mountains of Morocco and Algeria, and western North America as far south as Mexico. They are now found in extremely small numbers from western Europe and Palestine to eastern Siberia and the Himalayan region, possibly the Atlas Mountains of northwest Africa, and Hokkaido. Northern North American populations in Alaska and western Canada remain fairly stable. Many population in the United States have been extirpated, including those of the Sierra Nevada and southern Rockies. Northern Mexican populations were extirpated in the 1960's.
Physical Characteristics
Mass: 80 to 600 kg.
One of the largest of living carnivores, grizzly bears are 1 to 2.8 meters in length from head to rump and their tails are 65 to 210 mm long. They are 90 to 150 cm tall at the shoulder and can tower at an intimidating height of 8 feet when standing upright on their hind legs. They range in weight from 80 to more than 600 kg. On average, adult males are 8 to 10% larger than females. Ursus arctos is largest along the the coast of southern Alaska and on nearby islands where males average 389 kg and females average 207 kg, though some males have been weighted at as much as 780 kg. Size rapidly declines to the north and east, with individuals in southwestern Yukon weighing only 140 kg on average. Fur is usually dark brown, but varies from cream to almost black. Individuals in the Rocky Mountains have long hairs along the shoulders and back which are frosted with white, thus giving a grizzled appearance and hence the common name grizzly bear. Ursus arctos has an excellent sense of smell (able to follow the scent of a rotting carcass for more than two miles), human-level hearing, but relatively poor eyesight. Brown bears are extremely strong and have good endurance; they can kill a cow with one blow, outrun a horse, outswim an Olympian, and drag a dead elk uphill.
Food Habits
The diet of Ursus arctos consists mainly of vegetation and shifts to different foods as the seasons progress. In spring, grasses, sedges, roots, moss and bulbs are mainly eaten. During summer and early autumn, berries are essential, with bulbs and tubers also eaten. Ursus arctos consumes insects, fungi and roots at all times of the year and also digs mice, ground squirrels and marmots out of their burrows. In the Canadian Rockies, grizzly bears are quite carnivorous, hunting moose, elk, mountain sheep and goats, and occasionally black bears are preyed upon. In Alaska, Ursus arctos has been observed to eat carrion and occasionally capture young calves of caribou and moose. Grizzlies have also been observed to feed on the vulnerable populations of breeding salmon in the summer in these ares.
Reproduction
Mating of brown bears takes place from May to July, although the fertilized eggs are not implanted in the uterus until October or November. Births occur from January to March (usually while the female is still in hibernation) after a total gestation ranging from 180-266 days. Females remain in estrus throughout the breeding season until mating occurs and do not ovulate again for at least 2 (usually 3 or 4) years after giving birth. Two offspring are generally born per litter, and young are born blind and naked. They are weaned at 5 months of age but remain with the mother until at least their second spring of life (usually until the third or fourth). Brown bears mature sexually between 4-6 years of age, but continue growing until 10-11 years old. Bears have been known to live and reproduce in Yellowstone Park at 25 years of age, and potential lifespan in captivity is as great as 50 years.
Behavior
Ursus arctos may be active at any time of the day, but generally forages in the morning and evening and rests in dense cover by day. Brown bears may excavate shallow depressions in which to lay. Seasonal movements of Ursus arctos have been observed , with individuals sometimes travelling hundreds of kilometers during the autumn to reach areas of favorable food supplies, such as salmon streams and areas of high berry production. Home ranges can be as large as 2,600 sq km, but are on average between 73 and 414 sq km, with male ranges nearly 7 times greater than female ranges.
Home ranges overlap extensively and there is no evidence of territorial defense, although bears are genearlly solitary. Occasionally, bears may gather in large numbers at major food sources and form family foraging groups with more than one age class of young. Under these conditions, dominance hierarchies are usually formed and maintained with aggression. Highest-ranking individuals are large adult males, although the most aggressive bears are females with young. Least aggressive and lowest-ranking are adolescents. The only social bonds formed are between females and young. During the breeding season, males may fight over females and guard their mates for 1-3 weeks.
Ursus arctos begins hibernation in October-December, and resumes activity in March-May, with the exact period dependent on the location, weather, and condition of the individual. In certain southern locales, hibernation is very brief or may not occur at all. Most often, brown bears dig their own dens and make a bed out of dry vegetation. Burrows are usually located on a sheltered slope, either under a large stone or among the roots of a mature tree. Dens are sometimes used repeatedly year after year.
Ursus arctos moves with a slow, lumbering walk, although it is capable of moving very quickly and can easily catch a black bear. Brown bears are mainly terrestrial, although they can often be found swimming or preying upon fish in the water. Adults are unable to climb trees.
Habitat
Brown bears occupy a variety of habitats, but in the New World they seem to prefer open areas such as tundra, alpine meadows and coastlines. Historically, they were common on the Great Plains prior to the arrival of European settlers. In Siberia, Ursus arctos occurs primarily in forests, while European populations are restricted mainly to mountain woodlands. The main habitat requirement for Ursus arctos is some area with dense cover in which it can shelter by day.
Reference written by Liz Ballenger,
Biology 800 student.
University of Michigan.
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