Description

Male grizzly bears can reach and stand 2.44 meters (8 ft) tall on their hind legs; the females are on average 38% smaller, an example of sexual dimorphism. Their coloring ranges widely across geographic areas, from blonde to deep brown or red. The grizzly has a large hump over the shoulders, which is a muscle mass used to power the forelimbs in digging. The hind legs are more powerful, however. The muscles in the lower legs provide enough strength for the bear to stand up and even walk short distances on its hind legs, giving it a better view of its surroundings. The head is large and round with a concave facial profile. In spite of their massive size, these bears can run at speeds of up to 35 miles per hour. However, they are slower running downhill rather than uphill because of the large hump of muscle over the shoulders.

Grizzlies can be distinguished from most other brown bear subspecies by their proportionately longer claws and cranial profile which resembles that of the polar bear. Compared to other North American brown bear subspecies, a grizzly has a silver tipped pelt and is smaller in size. This size difference is due to the lesser availability of food in the grizzlies' landlocked habitats. They are similar in size, color and behavior to the Siberian Brown Bear (Ursus arctos collaris).

Diet

Although grizzlies are of the order Carnivora and have the digestive system of a carnivore, they are actually omnivores since their diet consists of both plants and animals. They have been known to prey on large mammals such as moose, deer, sheep, elk, bison, and even black bears. Grizzly bears also feed on fish such as trout. Grizzly bears readily scavenge food, behavior that can lead them into conflict with other species, such as wolves and humans.

The grizzly bears that reside in the American northwest are not as large as Canadian or Alaskan sub-species. This is due, in part, to the richness of their diet which in Yellowstone consists of whitebark pine pine nuts, roots, tubers, grasses, various rodents, army cutworm moths and scavenged carcasses, none of which match the fat content of the salmon available in Alaska and British Columbia. During early spring, as the bears emerge from their dens, elk and bison calves are actively sought. The bear moves in a zig-zag pattern, nose to the ground, hoping to find unsuspecting animals to feed on.

In preparation for winter, bears gain hundreds of kilograms of fat, during a period of hyperphagia, before going into a state of false hibernation. The bear often waits for a substantial snowstorm before it enters its den, such behavior lessening the chances that predators will be able to locate the den. The dens themselves are typically located at elevations above 6,000 feet on northern-facing slopes. There is some debate amongst professionals as to whether grizzly bears technically hibernate. Much of the debate revolves around body temperature and the ability of the bears to move around during hibernation on occasion. Grizzly bears have the ability to "partially" recycle their body wastes during this period. In some areas where food is plentiful year round, grizzly bears skip hibernation altogether.

Interspecies competition

Most notable in Yellowstone have been the interactions between gray wolves and grizzly bears. Since the reintroduction of gray wolves to Yellowstone, many visitors have witnessed a once common struggle between a keystone species, the grizzly bear, and its historic rival, the gray wolf. The interactions of U. arctos horribilis with the wolves of Yellowstone have been under considerable study. Typically, the conflict will be over a carcass, which is commonly an elk killed by wolves. The grizzly bear uses its keen sense of smell to locate the kill. Then the wolves and grizzly will play a game of cat and mouse. One wolf may try to distract the bear while the others feed. The bear then may retaliate by chasing the wolves. If the wolves become aggressive with the bear it is normally in the form of quick nips at its hind legs. Thus, the bear will sit down and ease its ability to protect itself in a full circle. Rarely do interactions such as these end in death or serious injury to either animal. One carcass simply isn't usually worth the risk to the wolves if the bear has the upper hand (due to strength and size) or to the bear (if the wolves are too numerous or persistent). Over time, it seems the grizzly bears have benefited from the presence of the gray wolf because of increased food availability.

Black bears generally stay out of grizzly territory but the grizzly may occasionally enter black bear terrain to obtain food sources both bears enjoy, such as pine nuts, acorns, and berries. When a black bear sees a grizzly coming it either turns tail and runs or climbs a tree. Black bears aren't really competition for prey because they have a more herbivorous diet than grizzlies. Confrontations are rare because of the difference in size, habitat, and diet of the bear species, but they do occur. When this happens it is usually with the grizzly being the aggressor. The black bear will only fight when it is a smaller grizzly such as a yearling or when the black bear has no other choice but to defend itself. This usually results in the black bear's death.

Cougars however, generally give the bears a wide berth. Grizzlies have less competition with cougars than with other predators such as coyotes, wolves, and other bears. When a grizzly descends on a cougar feeding on its kill, the cougar usually gives way to the bear. When a cougar does stand its ground, the cougar will use its superior agility and its claws to harass the bear yet stay out of its reach until one of them gives up, usually the cat.

Coyotes, Foxes, and Wolverines are generally regarded as pests to the grizzlies rather than competition, though coyotes and wolverines may compete for smaller prey such as rabbits and deer. All three will try to scavenge whatever they can from the bears. Wolverines are aggressive enough to occasionally persist until the bear ambles on, leaving more than normal scraps for the smaller animal.

Attacks on humans

Grizzlies are considered by some experts to be the most aggressive bears, even by the standards of brown bears. Aggressive behavior in grizzly bears is favored by numerous selection variables. Unlike the smaller black bears, adult grizzlies are too large to escape danger by climbing trees, so they respond to danger by standing their ground and warding off their attackers. Increased aggressiveness also assists female grizzlies in better ensuring the survival of their young to reproductive age. Mothers defending cubs are the most prone to attacking, being responsible for 70% of grizzly caused human fatalities. Historically, bears have competed with other large predators for food, which also favors increased aggression.

Precautionary measures

Grizzly bears normally avoid contact with people. In spite of their obvious physical advantages and many opportunities, they almost never view humans as prey. Even so, they can be extremely dangerous animals. Most grizzly bear attacks result from a bear that has been surprised at very close range, especially if it has a supply of food to protect, or female grizzlies protecting their offspring. In recent years, some grizzly bears appear to have learned to hone in on the sound of hunters' gunshots in late fall as a source of potential food, and inattentive hunters have been attacked by bears trying to appropriate their kills.

It is imperative for all campers in areas inhabited by grizzly to maintain a clean campsite. Reports have indicated that something as innocuous as a tube of chapstick can entice a bear to come near a campsite in search of food. Any bear that is conditioned to finding food around campsites will almost always return and expect the same reward. The bear is then a threat to campers and itself, and park rangers may be forced to kill it. For backcountry campers, hanging food between trees at a height unreachable to bears is a common procedure, although some grizzlies can climb and reach hanging food in other ways. An alternative to hanging food is to use a bear canister.

Since most grizzlies prefer to avoid people, it is a good idea to make noise when traveling in dense brush or other places where visibility is limited. High pitched shouts or whistles will alert nearby bears and give them a chance to get out of the way. "Bear bells" are generally useless as their sound does not travel far.

The Sierra Club wants the Forest Service to require everyone who enters a national forest in grizzly bear country to carry bear spray. Spokeswoman Heidi Godwin said in a news release: "The proper use of bear pepper spray will reduce human injuries caused by bears, reduce the number of grizzly bears killed in self defense, and help promote the recovery and survival of the grizzly bear."

Pepper-based bear sprays (containing at least 1% of the active ingredient capsaicin) have proven effective in deterring bears, both grizzly and black, that attacked after being surprised at close range. The spray causes instant irritation of exposed mucous membranes in the eyes, nose and mouth, and in the great majority of cases where it has been used, immediately diverts the bear. While just the surprise of a sharp spray can deter the bear, this cannot be counted on. Combined with most people's inexperience with firearms, the practicality of the firearm at hand, where to hit a bear if possessing one, and the suddenness of the situation, recent research has shown that bear spray is significantly more effective than firearms. A further advantage of bear spray is that it leaves the bear alive and perhaps less likely to attack in the future. However, bear spray is far from guaranteed, as a bear will either ignore it, or as in attacks on groups of two or more, the bear will sometimes simply move on to the next person. Also, if the can is not 100% full or reaches its expiration date, it may prove ineffective.

In the event of a surprise attack that cannot be repelled, it is important not to make eye contact with the bear as eye contact can be seen as aggression. Adopt a submissive posture and remain still; often a charging grizzly will turn away at the last moment. Never run from a bear—uphill, downhill or into water. Grizzlies can outrun humans. Some say that climbing a tree can be a good defense, if there is time, as the long curved digging claws of a grizzly makes it hard for the bear to grip a tree and climb it. Others argue that climbing trees is not a good idea since many bears can and will climb up after you. If you do take to a tree, you should get at least two to three times as high as the bear can reach.

Where grizzlies do follow through on a charge and actually attack, they will usually bite at the head. The best defense is to lie prone, face down, legs spread to make it harder for the bear to flip you over, and hands gripped around the neck. Normally, once a grizzly is sure you are no longer a threat, it will leave. This is why most wildlife agencies in grizzly country advise that people play dead if attacked. Struggling or fighting back will almost certainly intensify and prolong the attack; at the same there's an existing advice to actually fight back.

Grizzlies are driven by the need to find high-calorie food, especially first thing in the spring after hibernation and from late August through to their hibernation season in November. For this reason, people who live in bear country or camp, hunt or hike there, are well-advised to ensure that nothing that might smell edible to a bear is left exposed, especially overnight. Food and garbage should be locked securely in a hard-bodied structure or double-wrapped in plastic bags and suspended from a line at least 10 feet from the ground in campsites.

When traveling in grizzly territory, hikers should be aware of their surroundings at all times, recognizing the signs of bear presence in the area. Fresh diggings can indicate a grizzly recently feeding on vegetation or hunting rodents. A grizzly track is unlike that of a in that one can trace a single line from the innermost point on the left toe to the innermost point on the right toe without intersecting the pad of the foot. Claws are normally more than an inch from the end of the toe. Other signs include: talus slopes that appear raked, fallen logs which have been torn up, and high claw marks on trees. The smell of decomposing flesh is a danger sign, as bears will take possession of animal carcasses and defend these rich food supplies aggressively; hikers should always give a wide berth to any area where there is a strong odor.