Grizzly Bears in North America
Courtesy Tom Smith (firstname.lastname@example.org)
Grizzly bears are relative newcomers to North America. They evolved in Eurasia and arrived in central North America from Alaska only about 13,000 years ago, after the last continental ice sheets melted. Grizzlies spread south and east, but got no farther than central Mexico, the central Great Plains, and mid-way through Canada's boreal forests. It's not clear why grizzly bears did not expand farther. There is evidence that competition from resident black bears and newly arrived humans may have restricted their spread, and that the effects of competition were perhaps exacerbated by human-caused deaths. Although grizzly bears may have dominated Native Americans in places like southern California, the opposite was probably true in most of western North America.
The decline of grizzly bears started in earnest about 1850, at the time of first contact with significant numbers of spreading European settlers. The widespread extirpation of grizzly bears was rapid. Grizzly bears disappeared from about 95% of their former range in the contiguous United States by 1920 - within a mere 70 years. By 1970, grizzly
USGS Status and Trends of the Nation's Biological Resources - Grizzly Bear Page
bears remained in only about 2% of their former range, at about only 1% of their former numbers. The cause of this catastrophic decline is no mystery. Grizzly bears were extirpated because humans - primarily European settlers - killed them. However, extirpations were less rapid where grizzly bears lived in the mountains, and especially where they used foods that kept them at high elevations, out of harms way.
The rapid decline of grizzly bear range and numbers was dramatically reversed in the early 1970's, when grizzly bears were protected under the U.S. Endangered Species Act. There is compelling evidence that, without this protection, we would have only half the number of grizzly bears we do now in only about half the places. However, humans continue to threaten the remaining grizzly bears in the contiguous United States. About 1,000 grizzly bears survive in five ranges, although two ranges contain almost all of the bears. These two largest ranges are centered on Yellowstone National Park in Wyoming and the main range of the Rocky Mountains in Montana. During the 1990's bear populations were probably stable or increased and bears ranges seemed to expand. However, compared to losses experienced between 1850 and 1950, increases in bear range and bear numbers during the 1990's were small.
Courtesy Bob Housholder
Grizzly bears throughout North America continue to die primarily because humans kill them. In the U.S. Rocky Mountains, between 70 and 90% of all adult bears that die are killed by humans, despite protection under the Endangered Species Act. Grizzlies are killed primarily because they threaten human safety, because they destroy livestock or other property, because they are mistaken for a black bear, or because they are poached. They also tend to die more often in areas where there are roads and humans. The fate of grizzly bears is thus tied to the continued existence of large tracts of remote roadless habitat.
The survival of grizzly bears also depends on humans learning to live in grizzly bear habitat in ways that don't cause problems for the bears. Keeping garbage and other human-related foods away from bears is particularly important. Unfortunately, human populations are growing dramatically in and around grizzly bear range. Yellowstone's grizzly bear range is experiencing one of most rapid increases in human population of any region in the United States. At the same time,
Courtesy Dave Foreman
important grizzly bear foods are threatened. Whitebark pine, the source of heavily used whitebark pine seeds, is being eliminated by white pine blister rust (a virulent non-native fungal pathogen). Cutthroat trout, which are consumed by bears while they spawn, are being eaten by non-native lake trout. Meanwhile, all of grizzly bear habitat is in flux due to the ever-increasing effects of global climate warming. The fate of grizzly bears in the contiguous U.S. will likely depend on whether our increasing tolerance for bears and our increased ability to live with them offset the negative effects of increasing human populations and decreasing food supplies.