Bears have been part of the greater Yellowstone ecological system for thousands of years. Black bears evolved from bears that traveled to North America from Asia 7 to 8 million years ago. Their ability to eat a wide range of foods allowed them to survive the last ice age. Yellowstone is only one of the forested areas of North America inhabited by black bears. The grizzly bear, a subspecies of brown bear called “grizzled”, meaning gray, for the tips of its fur, is thought to be descended from the Ussuri brown bears that crossed from Asia to Alaska 50,000 to 100,000 years ago. They probably migrated south about 13,000 to 10,000 years ago. At one time they ranged as far south as Mexico, but now the Yellowstone region is the southernmost part of their range.
The black bear is the smallest species of bear living in North America, the females weighing from 90 to 275 and males weighing 125 to 550 as adults. They are four to six feet long and from two and a half to three feet high at the shoulder. Despite their name only about 50 percent of black bears in the Rocky Mountains are black. Black bears can also be brown or blond. They have a broad head and narrow muzzle, with a gradual slope from the top of the head to the nose. Their large, pointed ears are set far back on their heads. Black bears’ claws are short, typically 1.5 inches in length, and rounded and their tails are about 4.8 inches in length.
Brown bears aka Grizzly can be distinguished from black bears by their size, the shape of their snouts and their longer claws and by a mass of muscle seen on the tops of their shoulders. Male grizzly bears average around 500 pounds while females attain an average weight of 350 pounds. They are about 3 to 6.5 feet at the shoulder. Their snouts have a sharper angle from the head than those of black bears. Grizzlies’ claws average two to four inches in length. Although grizzly bears are typically dark brown, their coloring ranges from blond to black.
Bears are omnivores, eating both plants and animals. Black bears eat grasses, berries, nuts, fruit, seeds, insects, small vertebrates and carrion. They will climb a tree and claw it open to eat honey. Being highly dextrous, they are able to open jars and can develop a taste for human food, which makes them dangerous if fed or if humans are careless about where they leave food and garbage. Grizzly bears eat nuts, berries, bulbs and roots, wild fruits, pine nuts, bark, moths, insect larvae, elk, moose calves, smaller mammals and trout. As in the case of black bears, it is important to keep food away from grizzly bears so that they do not go to campsites.
Bears live alone except for reproductive functions. Black bears mate in the summer and one to five cubs are born after 63-70 days. Mothers care for their young for one and a half years. Female grizzlies have offspring every two to three years after the age of 5. They can have one to two offspring at a time, depending on how well fed the mothers are. After grizzlies mate the embryos implant only during hibernation and the cubs are born while the mother hibernates. Mothers barely wake when their cubs are born. A litter of 2 cubs is typical and the cubs are born weighing about a pound. Grizzly mothers care for their cubs for two years.
Bears in Yellowstone hibernate in the winter to survive the cold weather and lack of food when the ground is covered with snow, from October or November until March or April. Grizzly bears frequently dig dens or find natural caves near the bases of trees on north-facing slopes. It takes a grizzly bear 3 to 7 days to dig a den, moving as much as a ton of sandy loamy, clay loamy or rocky silt soil in the process. Insulating material such as spruce boughs is often placed in the den to keep the bear warm through the winter. Black bears also excavate or use north-facing caves or hollow trees. Winds in Yellowstone usually blow in a southwesterly direction, so snow accumulating on northern slopes helps to insulate the bears’ dens. Most dens are only slightly larger than the bear, so that the bear’s body heat is not lost.
Bears’ heartbeats and breathing slow down during hibernation and they go into a deep sleep, although they can be aroused when danger is present. Living on fat built up by eating during the summer, bears produce waste but do not defecate or urinate. Urea is broken down and used to maintain muscle and organs, while solid waste stays in the digestive system until spring. 15 to 30 percent of the bears body weight is lost during hibernation.
Cubs do not hibernate, and gain weight rapidly nursing from their mothers. At the age of three months black bear cubs weigh around 4 to 8 pounds and are able to follow their mothers out of the den. Grizzly bear cubs weigh about 10 to 20 pounds at ten weeks of age.
Bears emerge in the spring hungry and looking for food. Carcasses of elk or other animals frozen during the winter should be avoided by humans at anytime of the year, since they are a high protein attraction for bears. New spring vegetation is also a good food source for the hungry Yellowstone bears.
Between 1930 and 1969 injuries from bears became a problem as a result of tourists who fed the animals and open garbage pits filled by Yellowstone’s motels. In 1970, the Yellowstone park service made the decision to close the garbage dumps, make all dumpsters and trash cans bear-proof, and strictly enforce rules against feeding wildlife. Bears began eating natural foods and injuries were reduced in Yellowstone.
Tourists are urged to carry binoculars for bear viewing and to avoid contact. In 1910 two fatal maulings occurred when insects ate and killed white pine trees, taking away the bears’ source of pinecones and bark. The bears were then forced to go near people in search of food. If threatened by bears, tourists can protect themselves with commercially available bear repellant.
Just remember that as cute as Yogi Bear may be, his friends in Yellowstone Park are very dangerous. These guys don’t hang out at the mall at Christmas time.