The brown bear (Ursus arctos) is a large bear distributed across much of northern Eurasia and North America. Adult bears generally weigh between 100 and 635 kg (220 and 1,400 lb) and its largest subspecies, the Kodiak bear, rivals the polar bear as the largest member of the bear family and as the largest land-based predator. There are several recognized subspecies within the brown bear species. In North America, two types are generally recognized, the coastal brown bear and the inland grizzly bear, and the two types could broadly define all brown bear subspecies. An adult grizzly living inland in Yukon may weigh as little as 80 kg (180 lb), while an adult brown bear in nearby coastal Alaska living on a steady, nutritious diet of spawning salmon may weigh as much as 680 kg (1,500 lb). The exact number of overall brown subspecies remains in debate.
While the brown bear's range has shrunk and it has faced local extinctions, it remains listed as a least concern species by the IUCN with a total population of approximately 200,000. As of 2012, this and the American black bear are the only bear species not classified as threatened by the IUCN. However, the Californian, North African (Atlas bear), and Mexican subspecies were hunted to extinction in the nineteenth and twentieth centuries and the Marsican brown bear in central Italy is believed to have a population of just 30 to 40 bears.
Common characteristics of modern bears include large bodies with stocky legs, long snouts, shaggy hair, plantigrade paws with five nonretractile claws, and short tails. While the polar bear is mostly carnivorous and the giant panda feeds almost entirely on bamboo, the remaining six species are omnivorous, with varied diets.
With the exceptions of courting individuals and mothers with their young, bears are typically solitary animals. They are generally diurnal, but may be active during the night (nocturnal) or twilight (crepuscular), particularly around humans. Bears are aided by an excellent sense of smell, and despite their heavy build and awkward gait, they can run quickly and are adept climbers and swimmers. In autumn, some bear species forage large amounts of fermented fruits, which affects their behaviour. Bears use shelters, such as caves and burrows, as their dens; most species occupy their dens during the winter for a long period of sleep similar to hibernation.