A 2014 study revealed that brown bears peaked in activity around the morning and early evening hours. Although activity can happen day or night, bears that live in locations where they are apt to interact with humans are more likely to be fully nocturnal. In areas with little interaction, many adult bears are primarily
crepuscular, while yearlings and newly independent bears appear to be most active throughout the day. From summer through autumn, a brown bear can double its weight from what it was in the spring, gaining up to of fat, on which it relies to make it through winter, when it becomes lethargic. Although they are not full
hibernators and can be woken easily, both sexes prefer to
den in a protected spot during the winter months. Hibernation dens may be located at any spot that provides cover from the elements and that can accommodate their bodies, such as a cave, crevice, cavernous tree roots, or hollow logs. Brown bears have one of the largest brains of any extant carnivoran relative to their body size and have been shown to engage in tool use, which requires advanced cognitive abilities. This species is mostly solitary, although bears may gather in large numbers at major food sources (e.g., open garbage dumps or rivers containing spawning
salmon) and form social hierarchies based on age and size. Adult male bears are particularly aggressive and are avoided by adolescent and subadult males, both at concentrated feeding opportunities and chance encounters. Females with cubs rival adult males in aggression and are much more intolerant of other bears than single females. Young adolescent males tend to be least aggressive and have been observed in nonantagonistic interactions with each other.
Dominance between bears is asserted by making a frontal orientation, showing off canine teeth, muzzle twisting, and neck stretching, to which a subordinate will respond with a lateral orientation, by turning away and dropping the head, and by sitting or lying down. Brown bears also produce various vocalizations. Huffing occurs when the animal is tense, while woofing is made when alarmed. Both sounds are produced by exhalations, though huffing is harsher and is made continuously (approximately twice per second).
Growls and
roars are made when aggressive. Growling is "harsh" and "
guttural" and can range from a simple
grrr to a rumble. A rumbling growl can escalate to a roar when the bear is charging. Roaring is described as "thunderous" and can travel . Mothers and cubs wanting physical contact will bawl, which is heard as
waugh!, waugh!. Males always wander further than females, due to such behavior giving increasing access to both females and food sources. Females have the advantage of inhabiting smaller territories, which decreases the likelihood of encounters with male bears who may endanger their cubs. In areas where food is abundant, such as coastal Alaska, home ranges for females and males are up to and , respectively. Similarly, in
British Columbia, bears of the two sexes travel in relatively compact home ranges of . In
Yellowstone National Park, home ranges for females are up to and up to for males. In
Romania, the largest home range was recorded for adult males (). In the central Arctic of Canada, where food sources are quite scarce, home ranges range up to for females and for males. Brown bears are
polygynandrous, remaining with the same mate for a couple of days to a couple of weeks and mating multiply during the mating season. Outside of this narrow time frame, adult male and female brown bears show no sexual interest in each other. Females mature sexually between the ages of four and eight. Males will try to mate with as many females as they can; usually a successful male will mate with two females in a span of one to three weeks. Females come into
oestrus every three to four years, with an outside range of 2.4 to 5.7 years. The
urine markings of a female in oestrus can attract several males via scent. Dominant males may try to sequester a female for her entire oestrus period of approximately two weeks, but usually are unable to retain her for the entire time. Males take no part in raising cubs – parenting is left entirely to the females. Through the process of
delayed implantation, a female's fertilized egg divides and floats freely in the uterus for six months. During winter dormancy, the fetus attaches to the
uterine wall. The cubs are born eight weeks later, while the mother sleeps. If the mother does not gain enough weight to survive through the winter while gestating, the embryo does not implant and is reabsorbed into the body. Litters consist of as many as six cubs, though litters of one to three are more typical. The size of a litter depends on factors such as geographic location and food supply. At birth, cubs are blind, toothless and hairless and may weigh . There are records of females sometimes adopting stray cubs or even trading or kidnapping cubs when they emerge from hibernation (a larger female may claim cubs from a smaller one). Older and larger females within a population tend to give birth to larger litters. The cubs feed on their mother's milk until spring or early summer, depending on climate conditions. At this time, the cubs weigh and have developed enough to follow and forage for solid food with their mother over long distances. The cubs are dependent on the mother and a close bond is formed. During the dependency stage, the cubs learn (rather than inherit as instincts from birth) survival techniques, such as which foods have the highest nutritional value and where to obtain them; how to hunt, fish, and defend themselves; and where to den. The cubs learn by following and imitating their mother's actions during the period they are with her. Brown bears practice
infanticide, as an adult male bear may kill the cubs of another.
Dietary habits The brown bear is one of the most
omnivorous animals and has been recorded as consuming the greatest variety of foods of any bear. They often feed on a variety of plant life, including
berries, grasses,
flowers,
acorns, and
pine cones, as well as fungi such as
mushrooms. Among all bears, brown bears are uniquely equipped to dig for tough foods such as
roots,
bulbs, and
shoots. They use their long, strong claws to dig out earth to reach roots and their powerful jaws to bite through them. In spring, winter-provided carrion, grasses, shoots,
sedges,
moss, Brown bears living near coastal regions will regularly eat crabs and
clams. In Alaska, bears along the beaches of estuaries regularly dig through the sand for clams. With particular regularity, bears in
Denali National Park will wait at burrows of
Arctic ground squirrels, hoping to pick off a few of the rodents. In the Kamchatka peninsula and several parts of coastal Alaska, brown bears feed mostly on spawning
salmon, whose nutrition and abundance explain the enormous size of the bears in those areas. The fishing techniques of bears are well-documented. They often congregate around falls when the salmon are forced to breach the water, at which point the bears will try to catch the fish in mid-air (often with their mouths). They will also wade into shallow water, hoping to pin a slippery salmon with their claws. While they may eat almost all the parts of the fish, bears at the peak of salmon spawning, when there is usually a glut of fish to feed on, may eat only the most nutrious parts of the salmon (including the eggs and head) and then indifferently leave the rest of the carcass to scavengers, which can include
red foxes,
bald eagles,
common ravens, and
gulls. Despite their normally solitary habits, brown bears will gather closely in numbers at good spawning sites. The largest and most powerful males claim the most fruitful fishing spots and will sometimes fight over the rights to them. When brown bears attack these large animals, they usually target young or infirm ones, which are easier to catch. Typically when hunting (especially young prey), the bear pins its prey to the ground and then immediately tears at and eats it alive. It will also bite or swipe some prey to stun it enough to knock it over for consumption. In general, large mammalian prey is killed with raw strength and bears do not display the specialized killing methods of felids and canids. To pick out young or infirm individuals, bears will charge at herds so the more vulnerable, and thus slower-moving, individuals will become apparent. Brown bears may ambush young animals by finding them via scent. When emerging from hibernation, brown bears, whose broad paws allow them to walk over most ice and snow, may pursue large prey such as moose, whose hooves cannot support them on encrusted snow. On rare occasions, while confronting fully-grown, dangerous prey, bears kill them by hitting with their powerful forearms, which can break the necks and backs of large creatures such as adult moose and adult bison. Cannibalism is not unheard of, though predation is not normally believed to be the primary motivation when brown bears attack each other. Plants and fruit farmed by humans are readily consumed as well, including
corn, wheat,
sorghum, melons, and any form of
berries. Predation by tigers on denned brown bears was not detected during a study carried out between 1993 and 2002. Ussuri brown bears, along with the smaller black bears constitute 2.1% of the Siberian tiger's annual diet, of which 1.4% are brown bears. Brown bears regularly intimidate
wolves to drive them away from their kills. In
Yellowstone National Park, bears pirate wolf kills so often, Yellowstone's Wolf Project director Doug Smith wrote, "It's not a matter of if the bears will come calling after a kill, but when." Despite the animosity between the two species, most confrontations at kill sites or large carcasses end without bloodshed on either side. Though conflict over carcasses is common, on rare occasions the two predators tolerate each other at the same kill. To date, there is a single recorded case of fully-grown wolves being killed by a grizzly bear. Given the opportunity, however, both species will prey on the other's cubs. In some areas, grizzly bears regularly displace
cougars from their kills. Cougars kill small bear cubs on rare occasions, but there was only one report of a bear killing a cougar, of unknown age and condition, between 1993 and 1996. Brown bears usually dominate other bear species in areas where they coexist. Due to their smaller size,
American black bears are at a competitive disadvantage to grizzly bears in open, unforested areas. Although displacement of black bears by grizzly bears has been documented, actual killing of black bears by grizzlies has only occasionally been reported. Confrontation is mostly avoided due to the black bear's diurnal habits and preference for heavily forested areas, as opposed to the grizzly's largely nocturnal habits and preference for open spaces. Brown bears may also kill
Asian black bears, though the latter species probably largely avoids conflicts with the brown bear, due to similar habits and habitat preferences to the American black species. As of the 21st century, there has been an increase in interactions between brown bears and
polar bears, theorized to be caused by
climate change. Brown and grizzly bears have been seen moving increasingly northward into territories formerly claimed by polar bears. They tend to dominate polar bears in disputes over carcasses, and dead polar bear cubs have been found in brown bear dens.
Longevity and mortality The brown bear has a naturally long life. Wild females have been observed reproducing at 28 years, which is the oldest known age for reproduction of any
ursid in the wild. The peak reproductive age for females ranges from four to 20 years old. The lifespan of both sexes within minimally hunted populations is estimated at an average of 20 to 30 years. In captivity, the oldest recorded female was around 40 years old, while males have been known to live up to 47 years. While male bears potentially live longer in captivity, female grizzly bears have a greater annual survival rate than males within wild populations, per a study done in the
Greater Yellowstone Ecosystem. Annual mortality for bears of any age is estimated at 10% in most protected areas. Beyond predation by large predators – including
wolves, Siberian tigers, and other brown bears – starvation and accidents also claim the lives of cubs. Studies have indicated that the most prevalent cause of mortality for first-year cubs is malnutrition. Brown bears are susceptible to parasites such as
flukes,
ticks,
tapeworms,
roundworms, and
biting lice. It is thought that brown bears may catch
canine distemper virus (CDV) from other
caniforms such as
stray dogs and wolves. A captive individual allegedly succumbed to
Aujeszky's disease.
Hibernation physiology A study conducted by the Brown Bear Research Project did a
proteomic analysis of the brown bear's blood, organs, and tissues to pinpoint proteins and
peptides that either increased or decreased in expression in the winter and summer months. One major finding was that the presence of the plasma protein
sex hormone-binding globulin (SHBG) increased by 45 times during the brown bear's hibernation period. Although scientists do not yet understand the role of SHBG in maintaining the brown bear's health, some believe these findings could potentially help in understanding and preventing human diseases that come from a sedentary lifestyle. ==Relations with humans==