Life History
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.
In the winter when food is unavailable or scarce, most brown bears enter dens and sleep through the winter. 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.
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.
Range and Habitat
Brown bears (Ursus arctos), also known as grizzlies, 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.
Status, Trends, and Threats
Bear populations in Alaska are healthy and productive. Densities vary depending on the quality of the environment. In areas of low productivity, such as on Alaska’s North Slope, studies have revealed bear densities as low as one bear per 300 mi2 (777 km2). In areas abundant food, such as the Alaska Peninsula, Kodiak and Admiralty Island, densities as high as one bear per square mile (2.6 km2) have been found. In central Alaska, both north and south of the Alaska Range, bear densities tend to be intermediate, about one bear per 15-25 mi2 (39-65 km2). These figures do not mean that each bear has this much territory for its exclusive use. The area occupied by any individual bear overlaps those used by many other bears.