Rebounding Grizzlies Still Face, and Pose, Risks
Yellowstone's rebounding grizzly bear population is an undeniable success. But figuring out how to manage the threatened omnivores--in light of potential food shortages and deadly human-grizzly interactions--isn't so easy.
or decades grizzlies saw humans as a source of food. They concentrated at park dumps, where the waste from Yellowstone's massive tourism stream was left in piles for them to sift through. The dumps attracted so many bears that park officials even provided bleachers for the throngs of visitors who watched the animals scrounge and battle over refuse. Entire generations of bears became dependent on the dumps.
In 1959 John and Frank Craighead launched an intensive, pioneering study of Yellowstone's grizzlies. The brothers tranquilized, measured, collared, and tracked them. By then park officials had started worrying that feeding bears at open dumps was not consistent with their mandate to preserve wildlife in a natural setting. The Craigheads concurred, but a disagreement boiled over about how quickly to close the dumps.
The Craigheads were adamant that they should be phased out slowly so as not to create a food shock. But park officials decided to move quickly. Between 1968 and 1971 all the park's dumps were shut down and sanitized. The grizzlies fared about as the Craigheads had predicted. Human-bear interactions jagged upward as grizzlies spent more time in campgrounds. From 1968 to 1971 at least 140 grizzly deaths--about half of the Yellowstone ecosystem's population, the Craigheads estimated--were attributed to human causes. Grizzly populations in the park began a perilous decline. By 1975, when the bears were given ESA protection, their number in the park and its surroundings ranged from 136 to 312 individuals.
Those that did survive learned to be general omnivores again. Some had lived their whole lives without ever visiting the dumps, and their offspring prospered. Brown bears, of which grizzlies are a subspecies, are generalists. Which is why they're the world's most widely distributed bears, existing in conditions as varied as the salmon-rich estuaries of Kodiak, Alaska, and the protein-poor peaks on the Pakistan-Afghanistan border. Brown bears survive in Mongolia's Gobi desert and in Europe's remnant forests. They adapt to such varied conditions by learning to eat what's available. Historically, 60 percent to 70 percent of female grizzlies' diets in Yellowstone have consisted of plants and insects; the number is 30 percent to 50 percent for males. And the bears are brilliant at recognizing which food is available during specific times of the year, and from year to year.
In the courtroom, two specific food sources--whitebark pine seeds and Yellowstone cutthroat trout--formed the basis of a lawsuit that reversed the Bush administration's 2007 decision to delist Yellowstone grizzlies. "It seems paradoxically clear that the bears are not out of the woods yet," says Jeff Welsch, spokesperson for the Greater Yellowstone Coalition, which filed the suit that in 2009 returned Endangered Species Act protections to the grizzlies.
There's no argument that a sizable percentage of Yellowstone's grizzlies rely on whitebark pine seeds; in a bounteous year, for a significant number of bears, pine seeds might provide 90 percent of nutrition in the fall. And no one disputes that whitebark pines are dying throughout the northern Rocky Mountains. Climate change, disease, and the mountain pine beetle--all three inextricably linked--are driving the destruction. As the trees die, Welsch fears bears in the park's interior that depend heavily on the nuts will forage for other foods at lower elevations, pushing out toward park boundaries. The ripple effect could force other bears into more marginal--human-occupied--habitat. "When you have diminishing natural food sources bears start looking in places we don't want them to look," he says, recalling the dump closures. "Bear managers have done a fine job of bringing [grizzly recovery] to this point--it's a great success story--but until we're sure that they're able to adapt to a rapidly changing world, we'd better be careful with them, because grizzlies are Yellowstone."
The whitebark pine's extinction, should it occur, will happen gradually, Servheen counters. Besides, he points out, grizzly populations increased approximately three percent a year over the past 24 years, even though only half of those years produced bumper crops of whitebark pine seeds.
Meanwhile, populations of Yellowstone cutthroat trout, indigenous to Yellowstone Lake and its drainage, have crashed. Everyone agrees that lake trout, illegally introduced, are largely to blame. In Clear Creek, once an important cutthroat spawning artery--and once a protein source for some bears--cutthroat numbers slid from 70,105 in 1978 to just 538 in 2007. The same picture draws itself all over the drainage. Because lake trout spawn in deep water, they're beyond reach as a substitute protein.
And yet, says Servheen, it's not the end for grizzlies. "Cutthroat trout was a very, very, very minor part of the diet of very few bears in the Yellowstone ecosystem," he says. "Less than 10 percent of the population ate cutthroat trout for a couple weeks when they were available." Now those bears have switched to preying on elk calves, Servheen explains. "That's what makes grizzly bears grizzly bears--their ability to have such a diversity of diets."
The Ninth Circuit Court of Appeals based the bear's re-listing primarily on the whitebark pine uncertainties. Cutthroat weren't cited as a major concern, nor were environmentalists' assertions that regulatory mechanisms weren't adequate to protect the population should it begin spiraling downward.