Grizzly Bear Facts (Ursus arctos horribilis)

The grizzly bear (Ursus arctos horribilis) is a subspecies of brown bear found in North America. While all grizzlies are brown bears, not all brown bears are grizzlies. According to some specialists, the grizzly bear lives inland, while the North American brown bear lives on the coast due to its reliance on food sources like salmon. Meanwhile, the Kodiac brown bear lives in the Kodiac Archipelago of Alaska.

While habitat affects their appearance and behavior, there is no genetic difference between these bears. Thus, most scientists simply refer to any brown bear living in North America as a "North American brown bear."

Description

Brown bears are easily distinguished from black bears by their large muscular shoulder hump, short ears, and rump that is lower than the shoulders. Because they eat a lower protein diet, grizzly bears tend to be smaller than coastal brown bears, but they are still very large. The average female weighs between 130 and 180 kg (290 to 400 lb), while males typically weigh between 180 and 360 kg (400 to 790 lb).

Grizzly bears range in color from blond to black. Most bears are brown with darker legs and gray or blond tipped hairs on their back and flanks. Their long claws are well-adapted to digging. Lewis and Clark described the bear as grisley, which could have referred to the grizzled appearance of the bear's gray-or-gold-tipped fur, or to the gruesome ferocity of the animal.

Distribution

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Brown Bear Facts (Ursus arctos)

By Anne Marie Helmenstine, Ph.D.

Originally, grizzly bears ranged across much of North America, from Mexico through northern Canada. Hunting greatly reduced the bear's range. Presently, there are about 55,000 grizzly bears, mostly found in Alaska, Canada, Montana, Wyoming, and Idaho.

Diet and Predators

The grizzly bear, together with the gray wolf, is the apex predator in its range. Grizzlies pursue large prey (i.e. deer, bison, moose, elk, caribou, and black bears), smaller prey (i.e. voles, marmots, ground squirrels, voles, bees, and moths), fish (i.e. trout, bass, and salmon), and shellfish. Grizzly bears are omnivorous, so they also eat grasses, pine nuts, berries, and tubers.

Grizzly bears scavenge carcasses, and they will eat human food and garbage when available. The bears have been known to kill and eat humans, but about 70% of human fatalities are caused by females defending their young. While adult grizzlies don't have predators, cubs may be killed by wolves or by other brown bears.

Reproduction and Life Cycle

Grizzly bears reach sexual maturity around five years of age. They mate in the summer. Embryo implantation is delayed until the female seeks a den for the winter. If she does not gain sufficient weight over the summer, she will have a miscarriage.

Grizzly bears do not truly hibernate, but the female's energy is diverted toward gestation while she sleeps. She gives birth to one to four cubs in the den and nurses them until summer comes. The mother stays with her cubs and fiercely defends them for about two years, but then she chases them away and avoids them if the bears meet later in life. A female does not mate when caring for her cubs, so the grizzly has a slow reproductive rate.

Female bears live somewhat longer than males. The average lifespan is about 22 years for a male and 26 years for a female. This disparity is most likely caused by the injuries male bears incur while fighting for mates.

Grizzly bears can breed with other brown bears, black bears, and polar bears. However, these hybrids are rare because the species and subspecies don't usually have overlapping ranges.

Conservation Status

The IUCN Red List categorizes the brown bear, which includes the grizzly, as "least concern." Overall, the species population is stable. However, the grizzly is considered threatened in the United States and endangered in parts of Canada. Threats include habitat loss from human encroachment, human-bear conflict, pollution, and climate change. While the bear is protected in North America, reintroducing it into its previous range is a slow process, partly because the grizzly has such a slow life cycle. Even so, the grizzly was "delisted" from the Endangered Species Act in June 2017. As an example of the species' recovery, the grizzly population in Yellowstone National Park has risen from 136 bears in 1975 to about 700 bears in 2017.

Sources

• Herrero, Stephen (2002). Bear Attacks: Their Causes and Avoidance. Guilford, Conn.: Lyons Press. ISBN 978-1-58574-557-9.
• Mattson, J.; Merrill, Troy (2001). "Extirpations of Grizzly Bears in the Contiguous United States, 1850–2000". Conservation Biology. 16 (4): 1123–1136. doi:10.1046/j.1523-1739.2002.00414.x
• McLellan, B.N.; Proctor, M.F.; Huber, D. & Michel, S. (2017). "Ursus arctos". The IUCN Red List of Threatened Species. IUCN. 2017: e.T41688A121229971. doi:10.2305/IUCN.UK.2017-3.RLTS.T41688A121229971.en
• Miller, Craig R.; Waits, Lisette P.; Joyce, Paul (2006). "Phylogeography and mitochondrial diversity of extirpated brown bear (Ursus arctos) populations in the contiguous United States and Mexico". Molecular Ecology, 15 (14): 4477–4485. doi:10.1111/j.1365-294X.2006.03097.x
• Whitaker, John O. (1980). The Audubon Society Field Guide to North American Mammals. Chanticleer Press, New York. ISBN 0-394-50762-2.