An opportunistic feeder, the brown bear has a varied omnivorous diet which consists predominantly of berries and nuts, but also includes grasses, roots, insects, salmon, small mammals and large ungulates (2) (4). Larger animal prey may be either taken as carrion or actively hunted, particularly by grizzly bears. Probably the most carnivorous subspecies, these formidable predators can bring down moose, elk and even black bears. While the brown bear may be encountered throughout the day, it is mostly active during the early morning and evening. Seasonal movements are made in response to food aggregations, such as spawning salmon, during which time large numbers of bears may gather in relatively small areas (4). Brown bears have extremely large home ranges, varying from 200 to 2,000 square kilometres in males, and 100 to 1,000 square kilometres in females (2). While typically solitary, brown bears tolerate the presence of conspecifics and do not appear to be territorial, although adult males may fight for dominance (4).
During the mating season, from May to July, the males compete for females (4), and dominant males may attempt to guard a chosen mate from rival males while the female is in oestrus (5). Both males and females may mate with several different partners, and may also form short-lived pair bonds lasting from several weeks to a few hours (5). After mating, the fertilised eggs undergo delayed development and do not implant in the female’s womb until around November (2). Thereafter, the eggs continue development with the young born between January and March, resulting a total gestation period of 6.5 to 8.5 months (2) (4). The reason for this delayed development is that it causes the cubs to be born during the winter hibernation, allowing maximum time until the following winter for the cubs to grow large enough to survive hibernation without the mother (2). A litter of between one and four cubs is produced, which are weaned at five months and reach reproductive maturity at four to six years old (4). The first litter is usually produced between the ages of five and ten, and there is usually a period of two to five years between successful litters (2).
Like all northern bears, brown bears hibernate throughout winter, preserving energy by reducing heart rate and body temperature by a few degrees. Hibernation takes place in a den, often dug into a sheltered slope, in which the bear may survive for over half a year without eating, drinking, urinating or defecating (2) (4). This remarkable feat is achieved by utilising stored fat for energy and by recycling waste products normally excreted as urine to conserve fluids and produce amino acids. Incredibly, the female brown bear is also able to give birth and nurse a litter of cubs during hibernation, although the energetic cost is high and can incur a 40 percent loss of body weight (2).