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The Great Grizzly
Ever wonder what grizzly bears are really like? Follow along and read about the life of a grizzly bear. Find out how they mate, what they eat, and where they live.
- The grizzly bear is a North American brown bear. Its fur is typically brown but can appear to have white tips, which gives the bear its “grizzled” appearance and its name.
- Grizzly bears are found in only about 2 percent of their original range in the lower 48 states. They inhabit Montana, Wyoming, Idaho, and Washington. More than 500 grizzlies are living in the greater Yellowstone area.
- Grizzlies are one of the largest living carnivores. Male grizzlies generally weigh between 300 to 600 pounds and occasionally over 800 pounds, while females weigh around 200 to 500 pounds. They are about three feet tall at the shoulders, but can tower at an intimidating 9 feet when standing upright on their hind legs.
- Despite their impressive size, grizzlies are capable of great speed. Top speed is typically 35 mph, although a brown bear in Denali Park in Alaska was clocked at 41 mph!
- The grizzly’s life span is approximately 15 to 20+ years in the wild and 30+ years in captivity
- Grizzlies have a prominent hump between their shoulders and long claws. Both are adaptations that are related to feeding. The musculature and bone structure of the hump are adaptations for digging and for attaining the quick bursts of speed necessary to capture prey such as elk, moose, or bison.
- A grizzly’s sense of smell is seven times more powerful than a bloodhound’s. Grizzlies rely on a keen sense of smell to track their prey, and under the right conditions may be able to detect odors from miles away. Grizzlies may use their highly developed sense of smell to sniff out burrows of rodents, and use their long claws and muscle humps to excavate their prey.
- Grizzlies are not true hibernators. True hibernators are animals whose body temperature drops to a few degrees above freezing, and when disturbed, can take over an hour to wake up. A grizzly’s hibernation is more closely related to a long rest, and the bear can wake up quickly if disturbed. During hibernation the grizzly’s body temperature, normally 98.5 to 99 degrees, drops about 10 degrees to about 89 or 90 degrees.
- A grizzly has a four-chambered heart, just like a human. Its heartbeat is normally 40 to 70 beats per minute, but during hibernation, its heartbeat slows to 10 to 18 beats per minute.
- Grizzlies hibernate, or sleep, about six months a year. Females hibernate longer than males, especially if they have given birth to cubs.
- Grizzlies generally dig their own dens for hibernation and make beds out of dry vegetation. Burrows are often located on mountain slopes where deep snow may serve as insulation until spring. Grizzlies often dig under large stones or in the roots of mature trees. Bears may return to the same den areas year after year.
- Grizzlies become sexually mature between four and six years of age. Mating of brown bears occurs from May to July and females may copulate with several males during estrus, which lasts 10 to 30 days. Fertilized eggs develop to the blastocyst stage, but do not implant until November, when the female has begun hibernating. A six to eight week gestation follows, and births occur from January to March, usually while the female is still in hibernation. Total gestation time ranges from 180 to 266 days.
- The number of cubs born to a female ranges from one to three. Food supply, climate, and genetics are important in determining the number of offspring in a litter. Cubs are hairless, blind and toothless when born and weigh from 18 to 25 ounces. As soon as they are born, they begin nursing on their mother’s high fat, nutrient rich milk while the mother continues to hibernate.
- Cubs develop rapidly on this rich diet and weigh 10 to 15 pounds on average when the family group emerges from the den in the spring.
- Cubs normally stay with the mother for two and a half to three years and remain dependent on their mother’s milk for almost a year. The mother and cubs will remain in the den together for the next two years.
- The survival of the cubs is largely determined by the mother, who protects the cubs and teaches them feeding strategies and how to deal with danger.
- Male grizzlies do not contribute to the care of the young
- Sub adults are driven off by their mother at two to three years old. At this time, the adult female prepares to mate again. Sub adults often spend their first year of independence with siblings, offering one another security during a vulnerable time of life.
- When cubs leave their mother permanently, males establish ranges far away from home, while females settle more closely to their mother. Only about half of the weaned Yellowstone grizzlies survive to adulthood.
- Grizzlies are omnivores; top of the food chain predators, however 80 to 90 percent of their diet consists of green vegetation, wild fruits and berries, nuts, bulbs and roots. They also eat animals, from insects to rodents to elk, bison, moose, bighorn, sheep, deer, pronghorn and mountain goats. Grizzlies especially like newborn elk calves.
- The army cutworm moth is important in the diet of the grizzly bear. During peak periods when moths are abundant, bears can eat approximately 40,000 moths/day. Army cutworm moths have a nutritional value of approximately 72 percent fat, 28 percent protein and less than 1 percent carbohydrate
- The grizzly bear will eat approximately 20,000 calories a day. The ability to eat huge quantities of rich food and store fat without suffering from heart disease and associated cholesterol problems is of great interest to researchers. Studying the grizzly heart may unlock secrets that will help humans recover from or prevent heart disease.
- Climactic fluctuations and environmental changes cause the grizzly diet to change each year to adapt to new circumstances.
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