Grizzly Bear
The grizzly bear (Ursus arctos horribilis ) is actually a subspecies of the brown bear (Ursus arctos ). They are highly intelligent, curious and have an excellent memory, especially when remembering food sources. Their sense of smell is very acute, they have excellent hearing and can hear high pitches like a dog. They have good eyesight and can see color. Excellent runners, the grizzly bear can run uphill or downhill, and can reach speeds exceeding 35 miles per hour, faster than an Olympic sprinter. A male, or boar has an average weight of about 350 pounds, but have been known to grow as large as 900 pounds. Females, or sows are usually smaller than males and average around 275 pounds. The average bear is about 3 1/2-4 feet high at the shoulders when on all fours, and 6-7 feet tall when standing on its hind legs. Standing allows them to get more information from their senses. They have a distinctive shoulder hump which is actually muscle that allows the grizzly to be a powerful digger. Grizzlies have small round ears and a dished face profile rather than a flat one like the brown bear. Their front claws are 2-4 inches long, and curved to assist in digging. Grizzlies use these curved claws and powerful shoulder muscles to dig dens and find food such as roots, bulbs and rodents.
The grizzly bear is an omnivore, which means it will eat pretty much anything. During the spring grizzlies will feed on anything from winter-killed elk and bison to grasses, clover, dandelion, and other plants, even ants. Summer adds thistle, fireweed, bistort, roots, and mushrooms to the grizzlies diet, as well as spawning cutthroat trout, strawberries, and occasionally other berries. Once fall rolls around grizzlies will feed on roots, moths, and especially white bark pine nuts. Plants, berries, ants, and elk injured or killed in rutting balances out the grizzlies diet. The fall is an important time for grizzlies since they must find and eat enough food to last them the winter while they hibernate. Although they are not true hibernators, they do enter a form of hibernation both physiologically and behaviorally. Fat put on during the fall is metabolized during the winter, since bears do not eat, drink, urinate, or defecate for up to six months. During this time, their heart rate drops from 40-50 beats/min to 8-10 beats/min and their respiration slows to about 1 breath/min. Their body temperature does not change dramatically and only lowers by a few degrees, allowing bears to easily be aroused from their winter sleep. Dens are used only during this period of extended sleep, otherwise grizzlies sleep outside the rest of the year. This denning period usually lasts from October or November to March or April. Males are the first to emerge and females with cubs are last to emerge.
Breeding occurs during mid-May to mid-July, with mating occurring mainly in June. However fertilized eggs do not begin development until the start of the denning season because of delayed implantation. Cubs are born in January or February, and are about 1 pound at birth. Litter size is usually two cubs, but ranges from 1-4. Cubs will normally stay with their mother for 2-3 years.
Home ranges are dependent on food availability, but usually average around 250 square miles in size. Grizzlies once ranged from the Missouri River to the Pacific Ocean and from Canada to central Mexico, occupying plains, forests, mountains, beaches, and wetlands. Today their numbers have declined from as many as 100,000 to fewer than 1,000 in the contiguous 48 states. Grizzly bear currently inhabit 5 or 6 areas in Montana, Idaho, Wyoming and Washington, representing less than 1% of their former range. They were also the first animal to be protected under the Endangered Species Act of 1973. They were given a threatened listing in 1975 that still stands today.
Learn More
Trouble in Paradise [Home Range, Winter 2000]
PCA Puts On Bear Suit [Article, Spring 2000]
A Silver-Tipped Grizzly Bear or a Blond Black Bear? A Guide to Identifying a Bruin [Guest Article]
Grizzly Bear Information Clearinghouse
