Grizzly Bear

Quick Take

• Movies cast the grizzly as a human predator, but the data on who actually threatens whom tells a completely different story. See who the real threat is →
• A grizzly goes five months without eating, drinking, or doing something every other mammal must do daily, and the biology behind it is stranger than you'd expect. Explore hibernation biology →
• Biologists once classified nearly 90 separate grizzly bear species, and what collapsed that number to just one rewrites the bear's entire identity. Trace the classification history →
• There's a bear that's half grizzly and half polar bear, and when the two parent species face off, the outcome isn't what most people guess. Meet the pizzly bear →

The Grizzly bear is a type of brown bear that was once plentiful in the western and northwestern United States. The animal is also known as the North American Brown Bear. The name “grizzly” comes from the light tips on the bear’s fur, which give it a grizzled, or silvery, appearance.

Amazing Facts

• Fewer than 1,000 Grizzly bears live in the Lower 48 states.
• Grizzly bears are a threatened species in the United States.
• The California grizzly bear is extinct.
• The grizzly-polar bear hybrid is called the “pizzly bear.” In confrontations that pit polar bears vs. grizzly bears, in most cases the grizzly bear tends to prevail.

Classification and Scientific Name

The grizzly bear is a subspecies of the brown bear known as Ursus arctos. Ursus arctos horribilis is the scientific name for these bears. Ursus is Latin for bear, and arctos comes from Arktos, which is Greek for the word bear. Horribilis is a Latin term that means horrible.

Appearance & Behavior

Grizzly bears may be very light brown or dark brown. Grizzlies have large heads, dish-shaped faces, short round ears, and short tails. The stout bears have a large muscular hump on the upper back that provides strength for digging. The claws on the grizzly’s front paws are curved, large, and sturdy, which help the bear dig in the ground for food. The grizzly’s claws are also handy for turning over rocks to find insects. A male grizzly can stand eight feet tall — taller than any basketball player. The male can weigh up to 700 pounds. Females are smaller, weighing between 250 and 350 pounds. Grizzlies that live where food is plentiful tend to weigh more. The bears spend most of their time alone, roaming their habitat and searching for food.

Although the grizzly is a loner, it is not unusual to see several grizzlies feeding on the fish near rivers where salmon are plentiful. Grizzly bears hibernate or are inactive during the cold months. They store enough fat during the summer to sustain them during hibernation. Grizzlies dig a den or find a cave for hibernation. Once a grizzly enters hibernation, it rests there for about five months. During that time, the bear does not eat, drink, urinate, or defecate. In early spring, grizzlies come out of hibernation.

Evolution and History

While there may be some confusion, the grizzly bear is a subspecies of the brown bear, which migrated from Asia to North America 50,000 to 100,000 years ago. Then, the brown bear seems to have split into basically two groups: the coastal brown bear and the grizzly bear.

In the 1800s and early 1900s, biologists determined that there were many species of the grizzly bear — up to almost 90. As time went on, this diminished to fewer than ten, and now it is only one, which has been confirmed through genetic testing.

There are many similarities in appearance between the Kodiak bear (Ursus arctos middendorffi) and the grizzly bear (Ursus arctos horribilis), but they are both subspecies of the brown bear. In North America, if you see a brown bear, it could be just a brown bear, or it could be a Kodiak or a grizzly.

Habitat

Grizzlies require large areas of habitat for roaming and hunting. Females need between 50 and 150 square miles, and males require up to 600 square miles or more; however, grizzly habitats can overlap. The western United States was once a place where grizzlies roamed freely, as far south as Mexico. However, when settlers moved westward, rural development resulted in habitat loss. Human encroachment pushed grizzlies to higher ground, such as the Northern Rocky Mountains and other remote areas of the Northwest. The California Grizzly Bear, or Ursus arctos californicus, has been extinct since 1924, when the last grizzly was spotted in Sequoia National Park. The grizzly bear is California’s state animal, and the state proudly displays it on the state flag.

Of the approximately 1,500 grizzlies in the lower 48 states, most live in northwestern Montana and in or around Yellowstone National Park. Northern Canada and inland Alaska both have large numbers of grizzly bears. Although grizzlies are considered big game animals, in the continental United States, there are laws to protect the bears from becoming extinct. In 1975, the U.S. Fish and Wildlife Service placed the bears in the lower 48 states on the list of threatened species under the Endangered Species Act.

Humans continue to threaten the grizzly’s habitat. Bears that live near campgrounds can become accustomed to searching for food left behind at those sites and garbage disposal areas. Humans who feel threatened by the bears sometimes kill them. Illegal hunting and poaching remain threats to grizzly bears despite their protected status under the Endangered Species Act.

Diet

Grizzlies are omnivores, meaning they eat plants and animals. Grizzlies eat plant foods such as berries, grasses, roots, and mushrooms, as well as insects and animals like deer, elk, and mice. This bear is known for its love of fish and often lives near remote rivers. The bears are big eaters and can consume as much as 90 pounds of food each day, the equivalent of more than 350 large hamburgers. When food is scarce, the grizzly may rummage through trash or try to find food at a campground.

The grizzly’s hunting and eating habits play a role in keeping the ecosystem healthy in the areas where they live. When grizzlies consume plant-eating animals, it helps prevent those animals from ruining the plant life in areas where grizzlies roam. As they dig for food, grizzlies turn or till the soil. After feeding, grizzlies leave behind uneaten animal parts and carcasses that decay and serve as a natural fertilizer for the soil.

Predators and Threats

Movies and television shows portray grizzlies as aggressive toward humans. However, humans are the greatest threat to the bears. These bears keep to themselves and avoid humans. They will flee from dangerous situations but will become aggressive when threatened. If animals or humans try to harm grizzlies or their cubs, the bears can become violent quickly and will attack. About half of grizzly cubs do not live to reach adulthood because of diseases and grizzly predators that include mountain lions, wolves, and adult male grizzlies.

Reproduction, Babies, and Lifespan

Grizzlies breed when they are mature, between three and eight years old. The bears mate from May through July, with June and July being the peak months for breeding. During the mating period, a male spends about a month with a female and then leaves. The female goes into a den and hibernates during the winter. After about five months, between January and March, the female typically gives birth to two babies, known as cubs, but can produce up to four. Young grizzly cubs feed on their mother’s milk, which is high in fat. The cubs remain under their mother’s protection until they are about two years old. Half of all grizzly cubs are at risk of dying before reaching adulthood because of diseases and predators. Grizzly bears usually live to be 20 to 25 years old, but some can live up to 30 years.

Population

There are an estimated 1,500 grizzlies in the lower 48 states, down from 50,000 in the early 1800s. Alaska has about 30,000 Grizzlies, and Canada is home to 26,000. A light-colored grizzly called the grizzly-polar bear hybrid also lives in Alaska.