When Lewis and Clark explored the country, 50,000 to 100,000 grizzly bears roamed the wilderness of the West. As their habitat was destroyed by logging, mining, oil and gas drilling and land development, the powerful bears were threatened with extinction. Grizzly bears are an important symbol of wilderness and a key component of our unique Western wildlife heritage. Since grizzly bears are an umbrella species, the Endangered Species Act’s habitat protections for grizzlies also provides shelter for many other species of wildlife that share the bears’ home range. Today grizzly bears are recovering in areas such as Yellowstone and along the northern Continental Divide, yet still struggling in the Idaho panhandle, northwest Montana and the Cascades. In some places where bears are expanding, habitat loss and threats to key food sources have led to increased conflict with humans, and subsequently, additional grizzly bear mortality.
Grizzly bears reproduce slowly. Females may not have their first litter until they are 6 years of age. Therefore, recovery depends greatly on minimizing female mortality. This requires keeping them safely away from humans, our trash and our livestock because human-caused mortality is the number one threat to grizzly bears. This is why they survived modern human encroachment in the contiguous U.S. only in the most remote and rugged mountainous areas, though they once were common across much of the western mountains and plains.
Threats related to global warming
Global warming appears to be exacerbating human-caused grizzly bear mortalities. Grizzly bears are denning later in the fall due to global warming. This keeps them at risk from human-caused mortality for additional weeks during a time of year when grizzlies and hunters overlap. Grizzly deaths due to human self-defense often result.
Global warming is also causing some natural grizzly bear food resources to decline, forcing grizzlies to seek alternative foods. For example, Whitebark pine (Pinus albicaulis) seeds are a food resource for grizzly bears in some areas, including Yellowstone. Global warming has led to an increase in whitebark pine blister rust as well as an increase in competing species such as Douglas fir in higher elevations. As whitebark pine and other natural grizzly food resources decline due to global warming, grizzlies may shift from remote high elevation areas to lower elevation human-populated areas, looking for alternative foods. Here, they often encounter humans and our garbage, food and livestock. This causes bears to become conditioned to humans; these human-conditioned bears are often removed or killed by wildlife managers due to safety concerns.