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What happens when a protected predator eats an endangered species?

By Paul Rauber

Too small for heat or even much light, our base camp's tiny fire served only as a human gathering point in the midst of the vast moonlit bowl, 11,000 feet up in the John Muir Wilderness of the eastern Sierra Nevada. It was mid-October, on the verge of winter, and I was more exhausted than I cared to admit. I was among four volunteer porters carrying gear for Frank Green, a filmmaker who was trying to capture footage of the elusive Sierra Nevada bighorn sheep before the last one was killed and eaten. Whatever romance Sherpadom may have held faded within minutes of hoisting my 70-pound pack and starting the steep climb from the trailhead at Rock Creek Lake. No worse for wear, how-ever, was our ginger-bearded guide, John Wehausen, who lounged by the fire in perfect comfort. A biologist with the University of California's White Mountain Research Station and the preeminent expert on Sierra bighorn, Wehausen spends as many as 100 nights a year in the field. The day's hike hadn't much tired him. It turned out that he thought nothing of ascending 7,000 feet in seven hours on a single bottle of water. After studying bighorn sheep for 25 years, Wehausen was taking on the hardy qualities of his subjects.

They don't come much tougher than the Ovis canadensis californiana, a subspecies similar in appearance but genetically distinct from the bighorn sheep that range the mountain West from the Canadian Rockies to Baja California to West Texas. Sierra bighorn inhabit the highest, craggiest recesses of the Sierra Nevada, rarely descending below 10,000 feet except in the harshest winter months. Short and stocky-a big male weighs about 220 pounds-they are built for agility, not for speed. When danger threatens-most often in the form of a mountain lion-they run to the cliffs and move up as surely as if they had wings. John Muir called the bighorn "the bravest of all Sierra mountaineers."

Recently declared an endangered species, Sierra bighorn may never have been very numerous. Before they started appearing on Gold Rush menus, historical accounts suggest there were only about a thousand of them. Even deadlier than hungry miners were the domestic sheep that were brought to graze the high Sierra pastures-the "hooved locusts" against which Muir railed-and which passed on deadly respiratory bacteria to their country cousins. (In 1988, a thriving herd of 65 bighorn in the Warner Mountains in northeastern California was wiped out by contact with a single domestic sheep.) Though bighorn hunting was banned in 1878, by the end of the century Muir wrote that "few wild sheep, I fear, are left hereabouts."

In 1940, the Sierra Club proposed the creation of a bighorn sanctuary-a proposal rejected by the U.S. Forest Service, which feared that it would attract poachers more than protect the wild sheep. In 1971, sanctuaries were finally established on the spiny ridge of the eastern Sierra at Mt. Williamson and Mt. Baxter for the only two remaining populations (out of nine at the beginning of the century). By 1978, these herds numbered 250 animals.

For the next decade, working in part from data that Wehausen collected as a graduate student, sheep captured from the larger Mt. Baxter herd were used to restock three historic bighorn ranges, at Mt. Langley just north of Mt. Whitney, in Lee Vining Canyon (where they sometimes graze only feet away from the cars and trucks whizzing out of Yosemite National Park on Highway 120), and on Wheeler Ridge-beneath which we had pitched our tents.

The next morning, what looked from the bottom like a tough scramble up the ridge proved to be that and more, all loose scree and tippy, lurching boulders and dicey maneuvers it was just as well my wife didn't hear about. From the pass on top of the ridge the Owens Valley and White Mountains spread out to the east. We crouched low behind boulders, striving for inconspicuousness while Wehausen unpacked his telemetry equipment to see if any radio-collared sheep were in the vicinity. He picked up some weak readings, so we headed down the far slope, working southwest ridge by ridge toward a drainage known for its many avalanches as Barf Canyon. Resting atop the last ridge, we were set to scree-slide half a mile down to the next bench when Mike, one of the Sherpa crew, announced the presence of four ewes directly beneath us.

As quietly as possible in such rocky terrain, we moved downslope so as to avoid appearing above the sheep-a sure way to spook an animal whose survival depends on climbing higher than any pursuer. From an unthreatening vantage point we watched a valleyful of sheep-a total of 19, all ewes and lambs and yearling males. (Except for mating season, bighorn segregate by sex. During the rut, mature rams wander from one group of ewes to another.) Two young males worked their way up the vertical cliff across the cirque with effortless, economical grace: a leap, a bound, a pause, a pose at the ridgeline, and then they were gone. A ewe, two lambs, and a young ram picked their way up a talus slope until they disappeared by blending perfectly into the surrounding rocks. The lambs were nice and fat; Wehausen predicted that the female would be lambing by the next year. "Too bad she'll never get a chance to enjoy herself," lamented porter Dennis.

Some sheep we saw right away; others had to reveal themselves. "My job," said Wehausen, binoculars permanently glued to face, "is finding needles in haystacks-a rock with legs in the midst of a bunch of other rocks." It took the rifle-crack of a head-butt to alert us to two young rams facing off on a flat rock. Even so, I had trouble locating them. "The gray rock," said Dennis, trying to be helpful. "Oh. The gray one." (The only thing harder than finding a rock with legs is finding a rock without them.)

Autumn sun fading, we had a challenging climb back to the pass, up a slope a bighorn could have covered in a few minutes. With little energy left at the top, we still had to descend, by the light of headlamps, 1,400 feet of a boulder field that had yet to settle on its angle of repose. It was all worth it, though, for 30 seconds of satisfaction on a perfect scree field, striding straight down the mountain atop my own little landslide.

In camp, Wehausen sorted plastic bags of sheep scat. His aim was to collect samples from every last Sierra bighorn for genetic analysis (with declining numbers, inbreeding is a real concern). Despite the fine show we had that day, Wehausen was far from sanguine about the bighorn's prospects. In fact, at that time-October 1999-the Sierra bighorn seemed to be sliding down their own scree slope toward extinction.

Initially, the reintroduced herds drawn from Mt. Baxter had thrived. By 1985, there were an estimated 310 sheep in five locations. But then the numbers plunged, and by February of 1999, barely 100 adult animals remained. According to a petition for an emergency endangered-species listing filed by a variety of conservation organizations that month, "if current trends in sheep numbers and behavior continue, populations of these sheep could begin to disappear from the face of the earth within a few years."

When things get that bad, the harsh rules of population dynamics magnify every problem. The fewer the animals in a population, the greater the effect of acts of God: a broken leg, a harsh winter, even unfortunate distribution of the sexes. Following the severe winter of 1995, for example, the Mt. Langley herd was left with 4 ewes and 11 rams. That same year, an avalanche wiped out a dozen members of the Wheeler Ridge herd, reducing it by almost half.

What is causing the decline? Hunting is no longer an issue, and there has been no documented contact between domestic sheep and Sierra bighorn for 25 years. (This has been largely due to luck: In 1995, 23 domestic sheep escaped from a Forest Service grazing allotment adjacent to the Lee Vining herd's summer range, and were discovered within sight of the bighorn in Yosemite National Park-fortuitously, before they were able to mingle.) Rather than domestic sheep or sharpshooters, all evidence points to a natural cause for the bighorn's recent decline: Puma concolor, the mountain lion.

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