Class: Mammalia (Mammals)
Body length: 6 to 9.8 feet (1.8 to 3 meters); males are larger than females
Shoulder height: 3 to 4 feet (0.9 to 1.2 meters)
Weight: males—330 to 1,500 pounds (150 to 680 kilograms); females—215 to 660 pounds (97 to 300 kilograms)
Life span: 25 years in the wild, up to 40 years in zoos
Gestation: 6 to 8 months, including a 5-month delayed implantation period
Number of young at birth: 1 to 4 cubs (usually 2)
Weight at birth: 16 to 25 ounces (454 to 709 grams)
Age of maturity: 3 to 5 years
Conservation status: overall, species' numbers are declining and certain local populations are endangered or threatened.
• Bears are the only mammals that do not pee or poop for the entire time
they are in their winter sleep! In fact, by studying the way bears recycle
urine, doctors have been able to help human patients with kidney failure.
• Newborn bear cubs produce a loud, continuous humming while nursing, which is believed to help stimulate their mother's milk production. This noise is so loud, it can be heard from outside of the den!
• Brown bears will store carrion that they find and cover it with grass and moss. The moss contains chemicals that kill fungi and bacteria and acts as a preservative for the meat.
• Despite its "large" reputation, the grizzly bear Ursus arctos horribilis is actually one the smallest of the brown bear subspecies.
Mammals: Brown Bear
Range: northwestern North America, northern Asia, Europe, Atlas Mountains of northwest Africa, and the
A bear by any other name
Brown bears are brown, right? Well, maybe! They come in all sizes and shades, from a light cream color to almost black. It was once thought that there were 86 different kinds of grizzlies and brown bears in North America alone. Today, scientists agree that there is only one species of brown bear with a lot of variations! Bears in northwestern North America are called Kodiak, or Alaskan brown bears Ursus arctos middendorffi, and tend to be the largest of the species. This is from eating salmon that are rich in fat every summer. The Alaskan Peninsular brown bear Ursus arctos gyas has a much smaller range, just the western tip of the Alaskan peninsula. Brown bears in interior North America are known as grizzly bears Ursus arctos horribilis because their brown fur is tipped with white or tan; the word "grizzly means "sprinkled or streaked with gray." There are several brown bear subspecies found in Europe, Asia, the Middle East, and possibly Northwest Africa, but they are all smaller than their North American relatives.
Brown bears have a large hump of muscle on top of their shoulders and long front claws that make them powerful diggers. They dig large, cozy dens for their winter home. The bears spend four to six months a year curled deep in sleep in a den. That's one-third to one-half of their lifetime! This sleep is commonly called hibernation, but unlike true hibernation, the bears' body temperature does not drop drastically. However, the bears' heart rate slows from up to 70 beats per minute to only 10 beats per minute, their metabolism slows, and they do not urinate or defecate all winter! This "winter sleep" allows the bears to stay alive for a long period of time when there is little or no food available to them. Bears in warmer climates spend less of their time curled up in their dens than those in areas with a longer winter. In fact, the brown bear at the San Diego Zoo stays active year round!
Brown bear moms (called sows) perform an amazing feat while sleeping through the winter: they give birth! Breeding season occurs May to July, but implantation of the eggs is delayed for up to five months, and cubs are not born until January or February, during the coldest part of the winter. There are usually two cubs in a litter, and they are born almost hairless, toothless, and with their eyes sealed shut. They find their mother's nipples by heading for the warmth. Although the sow will sleep through the winter, the cubs spend their time nursing, wrestling, and keeping warm in her fur. The cubs' eyes open when they are six weeks old, and by the time spring comes around they have grown teeth and thick fur and are able to follow the sow outside the den.
During the winter, bears live off of the fat their bodies have stored up in the summer and fall. By the time they emerge from their dens in the springtime they are very hungry and may have lost up to one-third of their body weight. Sows with newborns are especially hungry and thin because they have been feeding extra mouths. However, most bears do not leave their den area right away, as it takes a while for them to completely wake up from their winter sleep. They will often make nests of leaves and grass near their den and sleep in the sun while the cubs play nearby. If a sow feels that her cubs are in danger she will chase them up a tree. But, unlike black bears, older cubs and adult brown bears do not climb trees. Luckily, there are not many animals that would challenge an adult brown bear; their biggest danger comes from other bears competing for food.
Brown bears are true omnivores and will eat anything nutritious that they find. Most of their diet consists of plant matter, but they will certainly eat meat if they can find it. Bears will dig for roots, tubers, and insects, scavenge for carrion, and even occasionally hunt prey such as rodents, young deer, and elk. However, the food that first comes to mind when one thinks of bears is salmon. The bears in Alaska and Russia will flock to the rivers used by salmon swimming upstream to spawn every summer. Brown bears live solitary lives once they leave their family, but the yearly salmon run brings many bears together. A social structure determines which bears get the best fishing spots. The large adult males (boars) get the first pick, then the sows with cubs. The solitary sows and subadults come next, and orphan cubs have to scrounge whatever scraps they can. At the beginning of the salmon run, the bears are very hungry and will eat all of the fish they catch except for the intestines. Once the bears aren't so hungry they will eat only the eggs, brains, and skin of the salmon, the most nutritious and fatty parts.
A bear of a tale
Brown bears have a fearsome reputation and do tend to be more aggressive than other bear species. However, each bear is different and usually won't attack humans unless it feels trapped. The brown bear once ranged throughout the Northern Hemisphere. Due to heavy hunting for meat, medicinal uses, and out of fear, the bear's range has shrunk considerably. Some cultures believe a bear's organs can cure certain illnesses; the bear's gallbladder is still highly prized in Asian markets and can fetch a high price. The species is not endangered, but as humans continue to put pressure on the bear's wild spaces, we are challenged to find ways to share space with this magnificent animal.