Grizzly bear

The grizzly bear (Ursus arctos horribilis) is a North American population—or subspecies—of the brown bear. It’s also called the North American brown bear or simply the grizzly. Besides the mainland grizzly (Ursus arctos horribilis), a few other living brown bear forms are sometimes labeled as grizzlies: the Kodiak bear (U. a. middendorffi), the Kamchatka bear (U. a. beringianus), and the peninsular grizzly (U. a. gyas). Two extinct forms also carry the name: the California grizzly (U. a. californicus†) and the Mexican grizzly (formerly U. a. nelsoni†). In parts of northeast Asia, the Ussuri brown bear (U. a. lasiotus) is occasionally called the “black grizzly,” though it’s no more closely related to North American brown bears than any other brown bear subspecies worldwide.

The name “grizzly” traces back to Meriwether Lewis and William Clark, who first wrote it as “grisley.” That word could have meant either “grizzly” (grizzled, with grey-tipped hair) or “grisly” (fear-inspiring, now usually “gruesome”). The modern spelling leans toward the first meaning, but naturalist George Ord formally classified the animal in 1815 as *U. horribilis*, referencing its character.

Several genetic studies have examined the grizzly’s history, and classification has shifted based on DNA evidence. Two morphological forms of *Ursus arctos* exist—the grizzly and the coastal brown bear—but these forms don’t have distinct mtDNA lineages. The grizzly genome was sequenced in 2018; it measures 2,328.64 megabase pairs and contains 30,387 genes.

Brown bears originated in Eurasia and first moved into North America between about 177,000 and 111,000 years ago. Most grizzlies belong to this initial wave (clade 4), which remains the dominant mitochondrial group south of subarctic North America. Genetic data suggest brown bears migrated south during Marine Isotope Stage 5 (roughly 92,000 to 83,000 years ago) when an ice-free corridor opened; the earliest fossils come from near Edmonton, dating to around 26,000 years ago. Other mitochondrial lineages appeared later—for instance, an endemic lineage in the Alexander and Haida Gwaii archipelagoes first shows up about 20,000 years ago. After a local extinction in Beringia around 33,000 years ago, two closely related lineages repopulated Alaska and northern Canada from Eurasia after the Last Glacial Maximum (more than 25,000 years ago).

In the 1800s, the grizzly was split into 86 distinct species. By 1928, that number had dropped to seven, and by 1953, only one species remained globally. Modern genetic testing confirms the grizzly is a subspecies of the brown bear (*Ursus arctos*). Biologist R.L. Rausch concluded that North America has just one species of grizzly. So everywhere it’s the “brown bear”; in North America, it’s the “grizzly,” but all belong to the same species, *Ursus arctos*.

In 1963, Rausch reduced North American subspecies to a single one, *Ursus arctos middendorffi*. Further Y-chromosome testing is needed for a more accurate taxonomy with different subspecies. Coastal grizzlies—often called “brown bear” or “Alaskan brown bear,” a geographically redundant synonym—are larger and darker than inland grizzlies, which is why they were once considered a separate species. Kodiak grizzly bears were also once thought distinct. At one point, five different “species” of brown bear were recognized, including three in North America.

How many subspecies of *Ursus arctos* exist in North America remains an open question. Traditionally, alongside *U. a. horribilis* proper, these have been recognized: Alaskan brown bear (*U. a. alascensis*), California grizzly bear (*U. a. californicus*), Dall Island brown bear (*U. a. dalli*), Alaska Peninsula brown bear (*U. a. gyas*), Kodiak bear (*U. a. middendorffi*), Mexican grizzly bear (*U. a. nelsoni*), ABC Islands bear (*U. a. sitkensis*), and Stickeen brown bear (*U. a. stikeenensis*). One mitochondrial DNA study found no distinct genetic groupings among North American brown bears, suggesting that previous subspecies designations are unwarranted and all should be considered populations of *U. a. horribilis*. The only genetic anomaly was the ABC Islands bear, which shows introgression from polar bears. No formal taxonomic revision was made, however, and taxonomic authorities haven’t accepted the implied synonymy. Additionally, a few studies suggest that some Alaskan brown bears—including the Kodiak and Alaskan Peninsula grizzlies—belong to a Eurasian lineage, more closely related to Siberian brown bears than to other North American ones. Until the systematics of North American brown bears is studied more thoroughly, other North American subspecies are provisionally kept separate from *U. a. horribilis*.

Grizzly bears rank among the largest brown bear subspecies, surpassed only by Kamchatka brown bears and Kodiak bears. Their size varies by timing and population. The biggest are coastal grizzlies on the Alaskan peninsula: males average 389 kilograms (858 lb), females 207 kilograms (456 lb). Populations in northern interior Canada are much smaller—males average 139 kilograms (306 lb), females 95 kilograms (209 lb)—similar to the local American black bear. Average total length for this subspecies ranges from 198 cm (78 in) to 240 cm (94 in), with an average shoulder height of 102 cm (40 in) and a hindfoot length of 28 cm (11 in). Newborn bears can weigh less than 500 grams (18 oz).