Grizzly bears (Ursus arctos horribilis) are brown bears found in North America, in areas such as Alaska and Canada. They are huge in size, weighing up to 36kg. Contrary to popular belief, they are just one of a number of subspecies of the brown bear, and can easily be differentiated from black bears.
Grizzly bears have a large range and need lots of space to live. They are omnivores and both an apex predator and keystone predator. They also hibernate in the winter months. Fortunately, these bears are listed as “least concern” on the IUCN Red List, and are not yet in danger of becoming endangered. There are currently about 60,000 wild grizzly bears located throughout North America.
Grizzly Bear Characteristics
Grizzly bears are very large and their thick fur ranges in color from an almost white tan to dark brown. Commonly, the fur on their legs is darker than their body, and they often have white or blond tipped fur on the flank and back, which gives them their named “grizzly”.
They have a big head with an elevated forehead, which gives them somewhat of a concave profile, and short, rounded ears. Their body has a large shoulder hump, where a mass of muscles attach to the bear’s backbone and give the bear additional strength for digging.
Males weigh between 180 to 360 kg (400 to 790 lbs) and females between 130 to 180 kg (290 to 400 lbs). The heaviest grizzly bear ever recorded was a male whose weight was reported to be up to 680 kg (1,500 lbs). Their height can range between 3.3 to 9.0 feet (1 to 2.8 meters), although they can measure even taller when standing on their hind legs!
The size of grizzly bears is scored on the basis of their skull measurement (length and width).
These bears have four paws, and each paw has tough pads that act like snow shoes. Each paw has five toes, and each toe has a claw, meaning a grizzly has 20 claws. They are very sharp, measuring two to four inches long, and give them the ability to dig for food and to dig their dens. Grizzly bears also have 42 teeth.
There are differences in the appearance of grizzly bears and black bears, which is how you can tell them apart. The grizzly has a rump lower than its shoulders, whereas black bears have a rump higher. Black bears also do not have humped shoulders, and have a straighter face and longer ears. Black bears have shorter claws, too.
The average age of a male grizzly bear is 22 years old, while the average age of females is 26 years old. However, the oldest wild grizzly bear lived for about 34 years in Alaska, and it is thought they could live up to around forty-five years old.
Male bears engage in seasonal breeding fights and this is why their life expectancy is shorter than females.
Grizzly bears are omnivores and eat a range of animals and plants. As an apex predator, they are at the top of the food chain and are not preyed on by any other animal. They eat insects, moose, bison, black bears, deer, elk, ground squirrels, caribou, carrion, salmon, trout, grass, seeds, berries and fungi. They normally eat injured or weak animals, and avoid healthy ones so there is less work when preying.
These bears have also been known to eat birds and their eggs, and sometimes attack the nests of bald eagles. They can also be a nuisance to farmers and cause economical loss as they can target cattle and sheep.
Grizzly bears may eat about 90 lbs (40 kg) food per day, which can mean they gain a body weight of around 2.2 lbs (1 kg) or more per day. In preparation for the winter, grizzly bears increase their food intake during the summer in order to put on weight. This is particularly important for females as they need sufficient fat reserves to give birth to and nurse cubs before leaving their winter den.
In coastal regions, such as in British Columbia and Alaska, grizzly bears supplement their diet with protein. For this reason, Alaskan or Canadian grizzly bears tend to grow bigger than those found in mountainous and other non-coastal regions.
Grizzly bears are solitary animals, with the exception of mothers and cubs, or if a plentiful food source is found. They use sounds, such as growling, moaning or grunting, movement, and smells to communicate.
They can run fast, at around 35 miles an hour for very short sprints, and are also good swimmers. Cubs are good at climbing trees to avoid danger, but they lose this ability as they get older. Grizzlies will often rub their bodies on trees to scratch and to let other bears know they are there.
Grizzly bears are one of the animals with lowest reproductive rate. They begin to look for mates in the spring and early summer, and females will mate with more than one male during her breeding season.
When a female grizzly becomes pregnant, the development of the embryo temporarily stops for several months. This is a process called “delayed implantation”, and allows the female time to get herself ready to carry a cub. If a female bear is unable to gain enough weight during the summer and fall, her body will tell her to not proceed with the pregnancy and the embryo will reabsorb.
When female grizzly bears enter hibernation, the embryo implants in her uterus. The gestation period is between 180 to 250 days and, in January or February, female grizzly bears give birth to one to four cubs (usually two). Newborn bears may weigh less than 500 grams (1.1 lb).
Mothers will care for her young inside the den until spring, feeding them milk, and are extremely protective. Once they leave the den after hibernation, they will begin to eat solid food as well as milk. They stay with their mother for around 2 years, but it can be longer if food is scarce. Grizzly bears reach sexual maturity at around 5 years old.
Grizzly bears hibernate at the beginning of winter, usually around late November, but the date depends on the temperature, food supply, and snowfall. In places where the climate is warm, such as California, bears do not hibernate. The main reason for hibernation is the cold weather and lack of food during this time.
They hibernate in dens, which are usually located on north-facing slopes an altitude of about 1,800 meters (5,900 feet). Before they hibernate, grizzly bears go through a period of hyperphagia or polyphagia (extreme sensation of hunger or strong desire for eating), and consume a large amount of food. During this time they can gain up to 180 kg (400 lbs)! Pregnant females are the first to enter dens, followed by females with cubs, and solitary males enter dens last.
While hibernating, grizzly bears do not eat or even go to the bathroom. They enter a deep sleep, and their heart beat slows from 40 beats per minute to only 8 beats per minute. However, their hibernation is not as deep of a sleep as some other hibernators, like bats or ground squirrels, and they will quickly wake up when disturbed.
Pregnant females give birth in the dens and nurse their cubs until they are large enough to venture outside in the spring. Male grizzlies wake up from hibernation in mid-March, while females and grizzly cubs are the last to leave the den, in about April or May.
Interaction With Humans
Grizzly bears are shy in nature and usually avoid humans. They are only dangerous when provoked or if a mother is trying to protect her cubs. Bears are around 3 to 6 times stronger compared to an average human!
If a grizzly bear attacks you, it is advised you do not run, lay flat on your stomach, and play dead. You should grasp your hands tightly behind your neck and spread your legs. This posture will make it harder for the grizzly bear to turn you over.
When preying on animals, grizzly bears usually stalk young, weak or injured animals. To find rodents and grubs, they will dig through the ground and overturn rocks. To catch fish, especially salmon, the bears will wait at the base of waterfalls and catch any that are leaping.
Location and Habitat
Grizzly bears are found in North American areas, and their range covers Alaska, much of western Canada, parts of northwestern United States (Washington, Idaho, Montana, and Wyoming), and extends as far south as Yellowstone and Grand Teton National Parks. In Canada, they can be found in British Columbia, Alberta, the Yukon, the Northwest Territories, Nunavut, and the northern regions of Manitoba. Their range can cover up to 600 miles, so they need a lot of space!
These bears used to be found in all of the western United States and south into Mexico, including the Great Plains and along rivers in desert habitats. However, control actions and habitat loss mean that they inhabit much less of the area nowadays — in fact, they only inhabit 2% of the area they used to!
The grizzly bear habitat can be diverse. They can live in woodlands, forests, alpine meadows, and prairies. They prefer areas away from human development and places that have space to dig their burrows and dens. They also enjoy areas along rivers and streams.
They can be found in a few national parks in the US, including Glacier National Park, Yellowstone National Park, Grand Teton National Park and Denali National Park.
Grizzly bears are considered a keystone species, meaning they are very important to the wildlife and environment. They help to distribute seeds as they eat fruits of many fruit-bearing plants and excrete seeds along with nutrients in their feces. They dig and turn over soil, too, helping to increase the amount of species in the ecosystem.
Grizzly bears also help to control the population of other animals within forests, which in turn helps with overgrazing in the forests.
After the bear species was eliminated from much of its original range, grizzly bears were placed under the Endangered Species Act in 1975. Because of this, their numbers have begun to grow again and they are now listed as “least concern” by the International Union for Conservation of Nature. While hunting of these bears in banned inside national parks, hunting is now permitted outside the boundary of Yellowstone National Park.
Humans are the biggest threat to grizzly bears, particularly if bears go into human-occupied areas to look for food or habitat and are killed. Hunting is also now permitted of these bears in certain areas.
Human development also contributes as a threat to these animals, as it results in habitat loss. Conservation strategies have been put in place to try to aid this. Climate change is another big threat to grizzlies, as it impacts food availability, as well as weather changes which affect their hibernation periods and allow for beetle infestation and fungal disease to grow on plants they consume.