Aquarium of the Pacific - Online Learning Center - Species Print Sheet
Conservation Status: Threatened - Protected
(Ursus arctos spp)Mammals • Terresterial
Brown bears are a symbol of America’s wildlands. In the time of the Lewis and Clark expedition they ranged over much of North America’s mid-plains, westward to California, and from central Mexico to Alaska and Canada’s Northwest Territory. Today only about 1,000 brown bears are found in the lower 48 states, where they have lost 99 percent of their former range.
At the Aquarium
The brown bear, extinct in California, is illustrated symbolically only as tracks on The Wave’s mosaic tile mural, Rios de la Vida (Rivers of Life). The fountain, mural, and accompanying graphics illustrate the story of our Los Angeles and San Gabriel Rivers. Although not on exhibit in the Aquarium, this bear is included in our website animal database to expand on the information touched on in The Wave fountain exhibit.
Canada’s Northwest Territories, British Columbia, western Alberta. United States - Alaska’s coast and Kodiak Archipelago islands, northwest Washington, Wyoming, western Montana, and Idaho. Also Europe, especially Russia, perhaps Japan and Mexico.
North American brown bears prefer open areas interspersed with forests for sheltering cover while resting. They inhabit tundra, alpine meadows, coastal plains near salmon runs, and rivers and valleys. Grizzlies range at lower elevations part of the year, moving to higher areas above 1800 m (6000 ft) where there are deep soils for digging a hibernation den and vegetative cover for roof support and isolation of it. Siberian bears are primarily forest dwellers while European bears prefer mountain woodlands.
All brown bears require an ecosystem of habitats that includes corridors for moving from one habitat to another. They establish home ranges to meet this need. Male ranges are about 322-805 km (200-500 mi) and female, 80-483 km (50-300 mi). They are territorial only during breeding season.
Brown bears have a large, heavily built body, a small head, high eye profile, a dish-shaped face, short thick ears, and a small tail and legs. They have high humped shoulders consisting of muscles that give strength for digging. The hump occurs less often in coastal bears. Interior bears lack the neck ruffles of coastal bears and some have a spectacled facial pattern. Claws are long, sharp, and non-retractable.
Color varies among the subspecies. In general, coastal bears are a creamy yellow to light brown with brownish legs and underparts; Kodiak, light brown, beige, or even blond; interior, dark brown to almost black. The brown bears in the Rocky Mountains, the grizzlies, get their name from the silver-tipped guard hairs on their back and shoulders that give them a frosted or silvery sheen appearance. There are white bears (not albinos) in portions of Alberta, Montana, and south central British Columbia.
The size of these bears is dependent on subspecies, food items and their availability, and length of feeding season. Because of their higher protein diets, coastal Alaska and Kodiak Island bears are significantly larger than interior and mountain bears whose diet is primarily vegetation.
Full growth is attained when these bears are 10-11 years old. Interior males weigh 136-272 kg (300-600 lb) and females, 91-181 kg (200-400 lb); coastal males, 363-544 kg (800-1200 lb) and females, 272-363 kg (600-800 lb); Kodiak males, 544-580 kg (1200-1500 lb) and females an average of 317 kg (700 lb). When interior bears stand on their hind feet to get a better view of their surroundings, they may be 1.8-2.7 m (6-9 ft) tall whereas Kodiak bears are 2.7-3.4 m (9-11 ft) in height.
Diet and Feeding
These bears are omnivores and food is a top priority in their lives. They generally forage in the morning and evening, resting in dense cover during the day. Their diet changes with the seasons as different food sources become available. They eat roots, fungi, insects, and small mammals at all times of the year. They use their long sharp claws and strong foreleg muscles to tear logs apart and turn over stones to get at the insects and their larvae and to dig out the burrows of mice, ground squirrels, and marmots. In the spring, just out of hibernation, they seek carrion of animals that did not survive the winter and early spring vegetation—grasses, sedges, and moss. In the summer and early autumn they gorge on food rich in protein and fat, so as to build up their fat stores to sustain them over their hibernation. These include berries, especially huckleberries, fruits, nuts, bulbs, and tubers. Their strong shoulder muscles are an asset for roto-tilling the soil to get at tubers.
They maximize their pre-hibernation weight gain by selecting the most nutritious portions of the food item to eat and the time of year when an item is most nutritious, such as berries when they are ripe and have the highest sugar levels; brains of small mammals, fish, and eggs of salmon or trout; only the eyes of salmon after they are satiated; internal organs of deer, elk, and cattle; and “spring-greenup”, the spring and early summer grasses.
Diet choices differ geographically. In Yellowstone National Park grizzlies fish for spawning trout, and Alaskan and Canadian coastal brown bears fish for spawning salmon. Bears in Glacier National Park follow wolf packs and mountain lions to remote regions using them as providers of meals of deer and elk. While 60-90% of the diet of coastal and interior bear is vegetation, that of the carnivorous Kodiak is much lower because of the inclusion of moose, elk, mountain sheep, and caribou in their diet.
Male and female brown bears become sexually mature at 4-6 years of age, but first pregnancies usually do not occur until the females are 5.5-7 years old. Males (boars) become territorial during the mating season, although their defense of the female against other males is usually not successful, with the result that both males and females mate with others during the about three week breeding season. Consequently, the cubs in a litter may have had different fathers.
Once the egg is fertilized, it divides several times. The embryo then remains suspended without implanting in the uterus (delayed implantation) until the female goes into hibernation in October or November. If the sow (female) has not eaten enough to sustain herself over the hibernation, the egg will not implant. After a 180-266 day gestation, one to four (average two) helpless cubs are born that are toothless, almost hairless, and unable to see or hear. They weigh about 241-368 g (8.5-33 oz) at birth.
When the family emerges from the den in March to May, the sow may have lost as much as 40 percent of her weight. In contrast, her cubs now weigh 6.8-9.1 kg (15-20 lb). Cubs stop nursing during July to September of their first year. In the two years that the cubs are usually with the female, she teaches them which foods to eat, where to find them, how to fish, and how to defend themselves. Aggressive in their defense, she may chase the cubs up a tree as a protective measure. She also swats them if they misbehave. If she becomes pregnant again in the cubs’ second year, she drives them away and enters hibernation alone. The sibling cubs usually hibernate together. There is a high predation of cubs by males seeking mates.
Brown bears communicate by smell and voice. They make moaning sounds when foraging and spread scent by scratching and rubbing on trees and other landmarks to communicate reproduction status and territorial boundaries during breeding season.
The exact time of brown bear hibernation is dependent on location, weather, and condition of the individual bear. They place a bed of dry vegetation inside a den that they have dug on a sheltered slope, under a large stone, or among the roots of a mature tree. Males and females have separate dens and females enter hibernation first emerging last. These bears are not true hibernators. Their respiration, heartbeat, and body temperature do not drop as low as true hibernators. They also can be awakened and may waken themselves to leave the den in search of food.
The size and strength of these bears puts them at the top of a food chain where they have little to fear from predators—all except humans. The long claws, strong leg and shoulder muscles of these bears are well adapted for digging dens and food. The short clawed cubs can climb but the long claws of the adults prevent them from climbing as black bears do.
As many as 50 percent of brown bears do not reach breeding age. Those that do may survive for 25 years.
Of four North American brown bear species, one, California’s golden bear ( Ursus arctos californicus has been extinct since 1922 and the northern Mexico silvery grizzly (U. a. nelsonii) is now believed to be extinct. The populations of Alaska’s Kodiak (U. a. middendorffi) and the common brown bear in Alaska and Canada (U. a. horribilis) appear to be stable. The lower 48 states U. a. horribilis population is listed as threatened except in areas of Montana and Idaho where there are experimental (non-essential) programs for reintroduction. Small pockets of brown bears of various subspecies exist in parts of Europe, Asia, and the Middle East. Most are either threatened or endangered.
Only about one percent of the former ranges of brown bears in the lower 48 states is left because of encroachment of human activities such as development, logging, mining, and road construction on their habitats, and illegal hunting to obtain their body parts for sale in Asian markets. In the states and Canadian provinces in which sport hunting is permitted, it is tightly regulated. For example, Alaska Fish and Game issues only 325 hunting permits a year out of 5,000 applications and requires that all non residents must be accompanied by a native guide. The cost of a non-resident license is $10,000-15,000.
Native people had many myths and legends about brown bears. After killing a bear, the inland Native American Sioux wore the hide in a dance that went on for several days in an effort to make peace with the bear’s spirit. The Alutiga (Kodiak natives) left the head of the killed bear in a field as a sign of respect for the bear.
Recent DNA studies support the theory of some scientists that polar bears are not a separate species of the genus Ursus (Ursus maritimus) but a subspecies, U. arctos maritimus. The theory is reinforced by the fact that the offspring of brown/polar bear matings are fertile.
Scientists are studying the denning physiology of brown bears in an effort to determine why they have low cholesterol levels in spite of their high fat diets, and why they are able to retain most of their bone mass and muscles and do not become uremic during hibernation in spite of the fact that they do not eat, drink water, urinate, or defecate.
A major food source for grizzlies in the Yellowstone area is army cutworm moths. In the summer these insects appear in huge numbers in the mountains at elevations above 3048 m (10,000 ft) where they feast on plant nectar in the early morning and then rest on rocks in swarms. This food supply causes congregations of grizzlies from distance and widely spread out home ranges to climb to the higher elevations where they each consume 10,000-20,000 moths a day. The moths are important sources of protein and fat for the bears’ weight gain prior to hibernation.