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Shy and reclusive, mountain lions share the tawny color of their African cousins, but bear a longer, heavier tail. They are extraordinarily adaptable, ranging from Canada to South America with the largest distribution of any non-anthropoid in the New World. In California, their prey of choice is mule deer, although a few have developed a taste for mutton. And therein lies the problem: When an expanding cougar population in the 1980s turned its attention to the Sierra Nevada bighorn, it drove the sheep to the brink of extinction.

In the past, mountain lions have themselves been victims of ruthless predators. California paid bounties for dead lions until 1963, and trophy hunting wasn't banned until 1972. In response to repeated attempts by the California Department of Fish and Game to reinstitute hunting, voters in 1990 passed Proposition 117 (strongly backed by the Sierra Club), declaring lions "specially protected" and prohibiting all hunting or control except in cases of predation on humans, pets, or livestock. Six years later, sport hunters and conservative legislators sought to overturn 117 with another statewide proposition, which was summarily rejected by the voters. The message was clear: Even though mountain lions are neither endangered nor even threatened, Californians didn't want to see them killed.

No one knows how many lions there were in California before European settlement or how many there are now. (Among the unknowable variables is the number of lions formerly killed by grizzly bears, now extinct in California.) Even so, most available signs point to an increase in their numbers following the end of bounty- and sport-hunting, which killed up to 400 cats a year. Reports of predation on livestock went from virtually zero in the early 1970s to over 300 in 1995. Attacks on humans occurred almost annually. Among radio-collared deer, lions were the primary cause of death. Meticulous records kept by employees of the Los Angeles Department of Water and Power of everything drowned in the L.A. aqueduct list no lions until 1988, but a dozen in the five years after that. And Wehausen was recording sheep after sheep dispatched by cats in the dwindling herds of the eastern Sierra.

What had been a successful bighorn reintroduction effort began to falter. Lee Vining Canyon lost a number of sheep, including one of its most productive ewes. Between 1976 and 1988, Wehausen documented 49 mountain lion kills in the winter range of the Mt. Baxter herd alone.

Almost all of these attacks took place while the bighorn grazed their winter ranges. The result was disastrous: The wild sheep stopped coming down from their high-mountain refuges, even in the howling blizzards of midwinter. In addition to putting themselves at increased risk of avalanches, they also lost access to the grasses that constitute an essential source of nutrients. Ewes that avoided the winter range, Wehausen found, lambed a month later than those that did not, and the snows and freezing temperatures took a heavy toll on lambs forced to overwinter on the mountaintops. The Mt. Langley herd, which numbered 42 in 1990, fell to 15 after the harsh winter of 1995. Lee Vining dropped from 85 to 29, recovered slightly over the next two years, but spiraled down to 17 after another hard winter in 1998. What had once been seen as a potential new translocation source became a basket case.

As we huddled around our little fire that night below Wheeler Ridge, Wehausen spun stories of a lifetime counting sheep, like the rare "play behavior" of well-fed bighorn in their winter range when the sheep get up on their hind legs and dance. And while head-butting generally occurs only between equal-age males, in this playful mood yearlings and aged rams would engage in mock combat: rearing up, charging, then pulling up short at the last moment, gently tapping their horns, and rearing up again to dance.

As the fire guttered, Wehausen told of lions, too, including the time he was pounced upon by a cougar protecting a fresh kill. Oddly, he recalled, he wasn't frightened: Even in mid-leap, something in the lion's demeanor telegraphed to him that it only meant to scare him off, not kill him. He did recommend the use of a hiking staff or similar long stick, which, he said, could keep a troublesome feline at bay indefinitely. I kept my own stick close by for the duration of the trip.

Since the sheep on Wheeler Ridge seemed to have moved south, our next approach was an 11-hour flanking dayhike from that direction. From Mosquito Flat, we quick marched past a lovely lake chain, over Morgan Pass, then north up a road that once serviced a large tungsten mine, where the gigantic pit mouths still gape amidst a postindustrial sci-fi wasteland of avalanche rock and twisted, rusting metal. Wehausen had other business below, so guiding us was Karl Chang, another indomitable eastside sheep researcher. Green and the other equipment-Sherpas trailing behind, Chang and I climbed a series of steep switchbacks to the bottom of the canyon, where we knelt behind a boulder to glass the surrounding slopes. Not 40 yards away stood a beautiful dark ram, which moved slowly away with a dignified air, pausing every 10 yards or so to turn his profile, finally disappearing around the corner.

The others arrived with the heavy camera equipment and asked if we had seen anything. There was a ewe far up on the eastern cliff, Chang said, but it had moved off over the mountain. "Well, there was that ram on the hill right there," I interjected. A moment's silence. "You're joking, right?" Chang said, dismayed. Rocks with legs reveal themselves selectively.

After lunch we ascended the canyon, 1,000 feet up a 35-degree slope until we reached the remnants of an old tramway that looked like an abandoned ski jump. Coming out on the northern peak at the old Adamson mine, we found ourselves with a sheep's-eye view of our first campsite. But, no sheep-at least until we turned back, and saw my dark ram grazing in our lunchtime meadow. We bushwhacked and scree-slid back down, but the bighorn faded back into the rocks. Once again, we finished our day by headlamp. Green, dispirited, walked back in the dark.

We returned to the nearby town of Bishop to clean up, and eat at a Chinese restaurant. Across from Wehausen was a large, garish painting of Chinese mountain sheep posed in a snowy forest. The biologist frowned. "Wrong habitat," he declared. "They prefer open country, like our sheep, and I'm not sure what species that is anyway . . ."

Cougars may have been the proximate cause of the bighorn's decline, but California's political process shares the blame. While Prop 117 allowed the state to relocate or kill a mountain lion that ate your heifer or poodle, it had no provisions for culling lions that lunched on vanishing species. Bighorn advocates and the Department of Fish and Game sought a legislative exemption, arguing that failure to control lions in the eastern Sierra would result in the disappearance of an animal endemic to the area since the last Ice Age.

In this effort they ran smack into the Mountain Lion Foundation-an organization fiercely protective of its namesake cat-which suspected Fish and Game of looking for a new excuse to kill big cats. An ugly brawl ensued, with mutual accusations of faulty science and "deceitful" arguments. Wehausen called the foundation "an animal-rights group, not an environmental group." For its part, the foundation sought (and still seeks) to minimize the role of mountain lion predation in the decline of the bighorn: "The historic cause of bighorn decline, and continued threat to survival," it argues, "is 130 years of human indifference and hostility to the bighorn's habitat needs. The facts are simple: predators kill bighorn one at a time; habitat loss and contact with domestic sheep decimates entire populations."

In its endangered-species listing, however, the U.S. Fish and Wildlife Service noted that "habitat throughout the historic range of Sierra Nevada bighorn sheep remains essentially intact . . . neither fragmented nor degraded." Nor has domestic-sheep disease been a problem in the recent past. Rather, wrote Wehausen, what "caused these sheep to decline over the past 15 years was apparently an unacceptably high level of mountain lion predation that developed in the 1980s, and nothing else."