After a 30-year struggle, grizzlies are multiplying throughout Yellowstone National Park as another top predator -- the gray wolf -- has helped build the bear population in a surprising way.
The numbers tell the success of grizzly bear restoration: About 650 bears roam the Yellowstone region today -- up from roughly 200 when the animal was first protected under the Endangered Species Act in 1975 -- and bears have expanded their range by 40 percent, says Chuck Schwartz, head of the Interagency Grizzly Bear Study Team.
Yet as robust as the recovery has been, new threats could affect the animals in the future. So many grizzlies roam Yellowstone that young bears search for new territory outside the park. Sometimes they kill livestock on surrounding private land, prompting ranchers and their political allies to seek removal of the bear's protected status.
But others say the bears should remain protected because threats to their food supply could undermine the progress of the last three decades.
Carcasses of elk and newborn calves that died in the winter provide food in spring. In summer, bears switch to native cutthroat trout spawning in dozens of Yellowstone streams as well as army cutworm moths that migrate en masse from farms to the blooms of the alpine tundra. In fall, whitebark pine nuts provide high-protein, fat-rich seeds.
Yet elk populations are down from a high of 10 years ago due to drought and more predators. Infestations of blister rust and bark beetle threaten whitebark pine nut production, which is erratic in the best of times. Biologists say lake trout that anglers illegally introduced to Yellowstone Lake and whirling disease have reduced cutthroat trout populations.
Enter the gray wolf, an unexpected source of grizzly aid. Since wolves were reintroduced to the park beginning in 1995 -- they number about 170 today -- bears have developed the habit of stealing their kills. John Varley, director of Yellowstone's Center for Resources, the park's science branch, says wolves provide food for at least 12 species, including bears, bald eagles and some beetles.
"The one thing we totally underestimated was how many other mouths [wolves] would feed," Varley says.
"In the Pelican Valley [of central Yellowstone], it's not if a bear will take a kill, but when," says Douglas Smith, Yellowstone's wolf project director. "Every documented ungulate [hoofed mammal] killed by a wolf pack in the last five years has been taken over by a grizzly."
Smith says that the highest number of grizzlies ever seen after wolf kills -- not just in the Pelican Valley but throughout the park -- was when the whitebark pine nut crop failed.
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