To serve as an introduction to the species before I begin logging my own observation notes, here’s a brief overview of the brown bears found in Katmai National Park. Their scientific name is Ursus arctos; they are commonly known as both the brown bear and the grizzly bear. From what I’ve been able to tell so far, the difference between the two is somewhat arbitrary, and has more to do with where they’re found rather than an actual difference in genetics. Those bears found closer to the coasts and relying more heavily on fishing (such as the ones at Katmai), are known as brown bears, while those found further inland, and may have access to mountain goats, sheep, and moose, are more often known as grizzly bears, a subspecies of brown bears (Ursus arctos horribilis).

Geography & Habitat

Brown bears occur throughout Alaska except on islands south of Frederick Sound in southeast Alaska, west of Unimak in the Aleutian Chain, and Bering Sea islands. They also occur in Russia, northern China, northern Japan, Europe, western Canada, and in limited portions of the northwestern United States. (Source: Alaska Department of Fish & Game)

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Image Source: Alaska Department of Fish & Game

Physical Description

Katmai’s brown bears are some of the largest bears in the world. They can stand 3-5 feet (.9-1.5 m) at the shoulder and measure 7-10 (2.1-3 m) feet in length. Most adult males typically weigh 600-900 pounds (272-408 kg) in mid-summer. By October and November, large adult males can weigh well over 1000 pounds (454 kg). Adult females average about 1/3 less in weight than adult males. (Source: National Park Service)

Brown bears in the wild can live for 20 to 30 years, although most brown bears die in their first few years of life. In captivity, brown bears have been known to live up to 50 years. (Wilson and Ruff, 1999)
Fur is usually dark brown, but varies from cream and light blonde to almost black. Individuals in the Rocky Mountains have long hairs along the shoulders and back which are frosted with white, giving a grizzled appearance, hence the common name grizzly bear in that region. 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.(Source: Animal Diversity Web, University of Michigan Museum of Zoology)

Mating & Reproduction

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. (Wilson and Ruff, 1999)

Female brown bears copulate with multiple males during estrus, which lasts 10 to 30 days. Males may fight over females and guard them for 1 to 3 weeks. Female receptivity is probably communicated by scent marking throughout her territory. (Wilson and Ruff, 1999) 

The brown bear mating system is polygynandrous (promiscuous), and takes place from May to July. Fertilized eggs develop to the blastocyst stage, after which implantation in the uterus is delayed. The blastocyst becomes implanted approximately 5 months after mating, usually in November when the female has entered her winter sleep. A 6 to 8 week gestation follows, with births occurring from January to March (usually while the female is still in hibernation). Total gestation time, including pre-implantation, ranges from 180 to 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 to three offspring are generally born per litter. (Source: Animal Diversity Web, University of Michigan Museum of Zoology)

Cubs are born in the den during January and February. Twins are most common, but litter sizes can range from 1 to 4. When the cubs emerge in June, they may weigh up to 15 lbs (7 kg) and they actively explore their world under the constant supervision of their mothers. Mothers can be furiously protective of cubs, however less than half of the cubs survive. Families typically stay together for 2 or 3 years and after separation female cubs tend to stay near where they were raised while males go farther afield. Most brown bears are sexually mature at 5 years old; however females often do not successfully produce a litter until later. The mating season is in the spring (May to July) and they are serial monogamous (have one mate at a time, but several each year). The oldest brown bear in Alaska was a 39 year old female, while the oldest male was 38. (Source: Alaska Department of Fish & Game)

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Image Source: National Park Service

Feeding & Predation

Brown bears are omnivorous, eating almost anything nutritious. Their diet changes with seasonal availability of different food sources. They eat a wide variety of plant foods, including grasses, sedges, roots, moss, and bulbs. Fruits, nuts, berries, bulbs, and tubers are taken extensively during summer and early autumn. They consume insects, fungi, and roots at all times of the year and also dig mice, ground squirrels, marmots, and other fossorial animals out of their burrows. Moth larvae have been demonstrated to be especially important sources of protein and fat when brown bears are putting on fat in the fall. In the Canadian Rockies and other areas, grizzly bears (the subspecies of brown bear in that area) are quite carnivorous, hunting moose, elk, mountain sheep, and mountain goats. Occasionally black bears are preyed upon. In Alaska, brown bears have been observed to eat carrion and occasionally capture young calves of caribou and moose. Brown bears have also been observed to feed on vulnerable populations of breeding salmon in the summer in these areas.(Source: Animal Diversity Web, University of Michigan Museum of Zoology) (Wilson and Ruff, 1999)

Brown bears are very adaptable and like humans, they consume a wide variety of foods. Common foods include salmon, berries, grasses, sedges, cow parsnip, ground squirrels, carrion, and roots. In many parts of Alaska, brown bears are capable predators of moose and caribou, especially newborns. Bears may also be attracted to human camps and homes by improperly stored food and garbage as well as domestic animals. (Source: Alaska Department of Fish & Game)

Although generally solitary in nature, brown bears often occur in large groups in concentrated feeding areas such as salmon spawning streams, sedge flats, open garbage dumps or on whale carcasses. Because of this, they have developed a complex language and social structure to express their feelings and minimize serious fights These feeding concentration areas also provide opportunities for people to watch bears. (Source: Alaska Department of Fish & Game)

Because of their size and aggressiveness towards threats, brown bears are not often preyed upon. Humans have persecuted them throughout recent history and some cubs may be attacked by other bears or by mountain lions or wolves, although this is very rare. (Wilson and Ruff, 1999)

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Brown bear, Eurasian subspecies (captive), 2006. Location: Urumqi Wildlife Park, Xinjiang Province, China. Photographer: David Blank. Image Source: Animal Diversity Web, University of Michigan Museum of Zoology

Social Habits & Communication

Bears are generally solitary creatures, but they predictably congregate around high quality food sources. To avoid physical conflicts, bears use a series of vocalizations and body posturing to express temperament and dominance. Less dominant bears (typically smaller subadult bears and females) yield space, like fishing spots, and resources, like a dead salmon, to more dominant bears (larger bears and adult males). Through the establishment of a fluid hierarchy, bears have evolved a social adaptation that allows them to avoid fighting in most instances. (Source: National Park Service)

Bears establish a hierarchy which allows them to interact with each other without violence (usually). It is based on a system of social interactions communicated through body posturing, scent, and vocalizations. In the hierarchy, subordinate bears typically yield space and/or resources to more dominant bears. In general large and mature males are most dominant, followed by females with cubs, other adult males and females, and subadults. A bear’s place in the hierarchy is based on its health, age, size, and disposition. The hierarchy is fluid and the rank of a bear can change from year to year or even season to season. (Source: National Park Service)

Brown bears communicate primarily through smells and sounds. Brown bears can be heard making moaning noises sometimes while they are foraging. They scratch and rub on trees and other landmarks to communicate territorial boundaries and reproductive status. (Wilson and Ruff, 1999)
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European brown bear (captive), 2002. Location: Zoo Stadt Haag, Austria. Photographer: Eva Hejda. Image Source: Animal Diversity Web, University of Michigan Museum of Zoology

Behavior & Hibernation

Brown bears begin a period of inactivity in October to December, and resume activity in March to May, with the exact period dependent on the location, weather, and condition of the individual. In southern areas, this period of inactivity is very brief or may not occur at all. (Source: Animal Diversity Web, University of Michigan Museum of Zoology)  Although this is not true hibernation, their body temperatures, heart rate, and other metabolic rates are drastically reduced. While in the den they do not eat, drink, urinate or defecate. Pregnant females are usually the first to enter dens in the fall. These females, with their newborn cubs, are the last to exit dens. Adult males, on the other hand, enter dens later and emerge earlier than most other bears. In northern areas, bears may spend up to 8 months in dens, while in areas with relatively mild winters, such as Kodiak, some male bears stay active all winter. (Source: Alaska Department of Fish & Game)

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. (Wilson and Ruff, 1999) Brown bears have an exceptionally acute sense of smell, exceeding that of dogs. Contrary to popular belief, bears are not nearsighted. Their eyesight and hearing are comparable to humans. They can run in short bursts up to 40 mph (64 kph) and are excellent swimmers. By all indications, bears are extremely intelligent and most have individual personalities. (Source: Alaska Department of Fish & Game)

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