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

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