The grizzly bear, scientifically known as Ursus arctos horribilis, is an iconic symbol of North America’s wilderness. This subspecies of brown bear is characterized by its immense size and strength. Adult males can weigh between 300 and 800 pounds, while females typically range from 200 to 450 pounds. A distinguishing physical feature is the prominent muscular hump above their shoulders, which provides the power necessary for digging. The common name “grizzly” originated from the silver-tipped, or grizzled, appearance of the guard hairs in their coat.
Geographic Distribution and Required Habitat
The historical range of the grizzly bear once stretched across North America, extending from Alaska down to Mexico and eastward to the Great Plains. This expansive distribution was dramatically reduced by westward expansion and settlement, resulting in the loss of nearly 98% of their former territory in the contiguous United States. Today, the species’ distribution in the lower-48 states is fragmented and confined to a few isolated populations within specific recovery zones.
Grizzlies are adaptable, but they require immense, undisturbed tracts of land to thrive. Their habitat encompasses diverse ecosystems, including high mountain forests, dense woodlands, open alpine meadows, and subalpine regions. Riparian zones along rivers and streams are particularly important, as they provide rich food resources. Habitat fragmentation from human development poses a significant challenge to their long-term survival.
Modern management efforts in the US focus on six recovery ecosystems. The Greater Yellowstone Ecosystem (GYE), spanning parts of Wyoming, Montana, and Idaho, is a primary example of this concentrated range. Similarly, the Northern Continental Divide Ecosystem (NCDE) in north-central Montana represents another large protected area.
Population Dynamics and Conservation Status
The dramatic decline of the grizzly bear population in the contiguous United States led to its listing as a threatened species under the U.S. Endangered Species Act (ESA) in 1975. Historically, an estimated 50,000 bears inhabited the western US, but this number plummeted to a low of approximately 700 to 800 individuals. Today, the total population in the lower 48 states has increased to an estimated 1,500 to 1,700 bears, with the majority concentrated in two main recovery zones.
Current population estimates are crucial for monitoring recovery progress and are specific to each ecosystem. The Greater Yellowstone Ecosystem population is estimated to be around 700 to 1,000 bears. The Northern Continental Divide Ecosystem supports a larger population, estimated at approximately 1,092 bears, demonstrating successful recovery efforts. Populations in other recovery zones remain much smaller, some with fewer than 100 individuals.
The slow reproductive rate of the grizzly bear is a major factor influencing the stability and pace of population recovery. Females typically reach sexual maturity between four and seven years of age, producing small litters averaging about two cubs. The average interval between litters is long, often over three years, as the mother must dedicate several years to raising her young. This combination of late maturity and infrequent reproduction means that populations are highly sensitive to human-caused mortality and habitat loss.
Core Behavioral Traits and Life Cycle
As an omnivore, the grizzly bear’s diet is highly variable and shifts dramatically with the seasons and regional availability of resources. Despite their formidable size, the majority of their food intake in many inland areas is plant-based, consisting of roots, grasses, and forbs, especially during the spring. Later in the year, they consume large quantities of berries to build up fat reserves.
Protein sources are also incorporated, ranging from insects like army cutworm moths to fish like salmon in areas where they are abundant. Grizzlies hunt large mammals, often targeting young or weakened prey like elk and moose calves, and they readily consume carrion. This varied diet is essential for preparing the bear for the winter denning period.
The annual cycle is punctuated by hibernation, a survival strategy to cope with periods of low food availability. Before den entry, grizzlies enter a phase called hyperphagia, characterized by a dramatic increase in food consumption, allowing them to gain significant fat reserves daily. Den construction and entry typically occur between August and November, where the bear’s metabolism slows significantly for several months.
Reproduction is closely tied to this cycle, featuring a unique biological process known as delayed implantation. Although mating occurs in the late spring or early summer, the fertilized egg does not implant in the uterine wall until November. Cubs, typically twins, are born in the den during January or February while the mother is still in a state of torpor. These cubs remain dependent on their mother for two to three years to learn survival skills before dispersing.
While generally solitary and territorial, grizzlies may congregate in areas of concentrated food, such as salmon spawning streams. Their temperament, especially that of a female with cubs, requires humans to adopt specific avoidance strategies. Proper food storage and waste management are emphasized in recovery zones to reduce conflicts, as human-caused mortality remains one of the largest threats to the species’ long-term recovery.