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Big Trouble For Bighorns

The Sheep Were Once Abundant in the Sierra nevada. But the Combined Impact of Hunters, Disease and Mountain Lions Has Put Them on the Brink of Elimination.


BISHOP, Calif. — Bighorn sheep were once abundant in the Sierra Nevada, with more than a dozen different herds traversing the rocky, high elevations of the range's steep eastern slope.

Today, the animals are on the brink of being eliminated from the Sierra. As of last summer, only about 150 bighorns were left in the entire range.

According to John D. Wehausen, the foremost researcher of Sierra bighorns, the last of the sheep are now being eradicated by mountain lions. A recently enlarged population of lions on the east slope of the range is preying on bighorns, and even more significantly, the sheep have stopped descending to their low-elevation winter range because of fear of the lions there, Wehausen said.

The abandonment of the winter range has been disastrous for the sheep because it holds highly nutritious forage that they need to survive.

"Mountain lions have caused a behavioral change in bighorn sheep in the Sierra," Wehausen said. "The sheep don't come down to the base of the mountains to get the forage they need, and they suffer for it. Also, we're seeing predation levels we've never seen before."

Among the reasons Wehausen cites for the increase in lions are the end of state bounties on the animals in the early 1960s and the cessation of mountain lion hunting in the 1970s, capped by the passage of a 1990 California ballot initiative that made it illegal to kill mountain lions except in some extreme situations.

Wehausen, an independent researcher, is highly respected in the wildlife science community and referred to as "the sheep god" by other biologists, with only partial irony. After doing his doctoral work at the University of Michigan on Sierra bighorns in 1974, he moved to the Sierra and has spent every year since hiking the Sierra back country and observing the sheep firsthand.

However, the idea that a predator like the mountain lion could be responsible for the elimination of an entire population of prey species is somewhat controversial. Howard Quigley, president of the Hornocker Wildlife Institute in Idaho, known for its work in conserving tigers in Siberia and with mountain lions and other predators in North America, is familiar with Wehausen's studies of Sierra sheep.

"It's counter to a lot of predator-prey theory in field science, but California has an unusual wildlife situation, too," Quigley said. "It is a strange situation to have mountain lions suddenly controlling a population like that. Most mammalian predators, whether it's wolves, mountain lions, African lions, whatever, their greatest impact on sheep, deer, elk or other ungulate populations is always when the populations are at their lowest.

"The real scientific inquiry here is not necessarily, 'Are lions controlling this sheep population?' I think John has shown that this is happening, and perhaps we need to do something about the lions if we want bighorn sheep on the east side of the Sierras. The real intrigue is, why is this happening?"

Sierra bighorns have been harmed by a variety of factors since the region was settled in the mid-1800s. In the last century, market hunters killed many of the sheep. Wehausen reports seeing a restaurant menu from the 1800s Sierra mining camp of Bodie that listed bighorn sheep as a dinner item. Far more devastating to Sierra bighorns were bacterial and viral diseases transmitted by the domestic sheep that were often herded in the region. Domestic sheep also severely overgrazed the Sierra, and sheepherders sometimes killed bighorns on sight because they considered them unwanted competitors.

By 1978, Sierra bighorn numbers had dwindled to 250 animals in two herds. In the 1980s, the California Department of Fish and Game began a program to increase their numbers by creating new herds within their native range. Animals from the Mt. Baxter herd in the southern Sierra were captured in nets and trucked to other parts of the range. One herd was reestablished just outside the eastern boundary of Yosemite National Park.

Initially, the program was successful. By 1986, with three new herds established, the total number of bighorns in the range grew to 310. But in the 1990s, the number of animals dropped dramatically to its current level because of mountain lions. One herd on Mt. Williamson now has only one animal remaining.

The state of bighorns in the Sierra may be seen as an even more urgent problem if other recent work by Wehausen and another wildlife researcher, Rob R. Ramey of the University of Colorado, gains acceptance by wildlife scientists. The two researchers, using genetic testing, skull measurements and other techniques, have concluded that the bighorns in the Sierra are a separate subspecies, rather than members of a broader subspecies extending from Northern California into British Columbia, as was previously believed.

If they are correct, it would mean not only that Sierra bighorns are in danger of disappearing, but also that one of only four subspecies of bighorns is on the brink of extinction.

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