SHEEP SAVIORS SCIENTISTS WORK TO PROTECT ENDANGERED BIGHORN.

Byline: BILL BECHER

YOSEMITE HIGH COUNTRY - Tom Stephenson and Cody Schroeder are searching a snowy ridge with high-powered binoculars. The winter air is biting, and the two hunker down out of the wind.

Mt. Dana, the second highest peak in Yosemite National Park, looms nearby.

The two scientists are looking for the endangered Sierra Nevada bighorn sheep that live in some of the most scenic terrain in California.

Being a bighorn sheep scientist is tough physical work.

Stephenson, a biologist with the California Department of Fish and Game (DFG), and Schroeder, a graduate student, made the arduous trip to Lee Vining Canyon to check on the bighorns. Tioga Pass Road, which bisects Yosemite National Park, is closed in winter. Caltrans crews had just begun to clear the snow.

After driving to the end of the plowed section, Stephenson hoisted a directional antenna and listened for the signals from the radio collars that have been fitted to about 30 of the remaining sheep.

The two then unloaded snowmobiles and rode them over the snow-covered road to Saddlebag Lake. At the lake, the scientists donned telemark skis and crossed the still-frozen lake then climbed a 1,000-foot high ridge above the lake. They took off their skis and hiked to the crest of the ridge.

Stephenson spots seven sheep - four ewes and three lambs - grazing below a peak near the boundary of the Hoover Wilderness.

The sheep's ancestors crossed the Bering Sea when there was a land bridge from Asia about 30,000 years ago. If they had known what was in store for them, they might have stayed in Siberia.

Conservationist John Muir once called bighorn sheep the ``animal mountaineers of the Sierra.''

Now these nimble creatures are in danger of extinction. Scientists like Stephenson are trying to save them.

The bighorn sheep depend on their incredible agility to evade the mountain lions and coyotes that prey on them. Golden eagles can kill lambs by knocking them off of cliffs. For protection from predators, the sheep graze close to escape routes that lead to the rocky crags of the High Sierra where the lions and coyotes can't go.

The extreme alpine environment also takes its toll. The bighorn sheep must contend with avalanches, falls from cliffs and starvation in extreme winter weather.

``When you get above the tree line in the Sierra Nevada it's incredibly harsh,'' said Stephenson. ``There is very little vegetation. The soil is barren and rocky. Even in the best of circumstances it's a hard place to make a living.''

Bighorn are stocky, with white to brown coats and a distinctive white patch on their rumps. The males, called rams, weigh up to 220 pounds. Their namesake C-shaped horns are wide and flaring. When competing for females, the rams butt heads in dominance contests that would make a good aspirin commercial. Rams and ewes live most of the year in separate herds, coming together in the fall mating season.

Miners killed bighorn sheep for food during the California Gold Rush. In 1878, the California legislature prohibited hunting bighorns. But their numbers have continued to plummet over the last century.

The heavy winter of 1995 took a toll. An avalanche killed a dozen sheep on Wheeler Ridge. By the following spring there were only about 125 Sierra Nevada bighorns left.

Contact with domestic sheep is likely the cause of most of the long-term decline. Sierra Nevada bighorn sheep have no immunity to the respiratory diseases they contract from domestic sheep grazing in the Eastern Sierra.

Predation by mountain lions also has played a somewhat controversial role.

Historically the sheep have lived in balance with the lions, but as sheep numbers declined to near the vanishing point in the 1990s predation by mountain lions became a concern. One scientist theorized that the sheep were abandoning their lower altitude habitat because of the mountain lions and more sheep were being killed by avalanches and starvation as a result of this displacement.

The Wildlife Protection Act passed by California voters in 1990 made mountain lions a specially protected species, removing the ability of the DFG to save sheep by killing mountain lions.

In 1999 the Sierra Nevada bighorn sheep were given emergency Federal protection as an endangered subspecies, trumping the California law. Several mountain lions were killed by the DFG in an attempt to save the bighorn from possible extinction. While it's certain that mountain lions kill bighorn sheep, it's not clear if the lions caused the behavioral changes in the 1990s.

DFG scientists manage the sheep and lions together - they even share an office in Bishop. When a lion must be killed, it's a ``surgical strike'' of a problem animal said Tom Stephenson, the biologist overseeing the bighorn recovery program.

The DFG is the lead agency charged with developing and implementing a recovery plan for the bighorn sheep. The plan calls for reducing natural mortality of the sheep, avoiding contact with domestic sheep and expanding the number of herds by relocating sheep.

The scientists collected samples of the sheep droppings, which will be sent to a lab for analysis. From the samples the biologists can find out what the sheep have been eating, how nutritious the food is, and analyze DNA to determine the genetic makeup of the individual animals.

Biologists also capture sheep using net guns fired from helicopters. The sheep are examined by ultrasound to check on their general condition and body fat and for pregnancy in ewes. Then the sheep are weighed, measured, fecal and blood samples are taken, and the sheep are fitted with radio collars before being returned to the wilderness.

The scientists use both conventional and downloadable Global Positioning System (GPS) collars that use satellite signals to track the sheep's movements. The sheep move to higher elevations in summer and lower in winter.

The good news is that sheep populations have recovered somewhat. There are about 250 to 300 sheep now. The majority of the population is in two herds, one on Wheeler Ridge and the other in the Mt. Baxter and Sawmill Canyon area. The bad news is that scientists feel that at least three times as many animals are needed to be sure of their long-term survival.

Why does Stephenson work so hard to keep the bighorns from dying out?

``This species is one of the rarest mammals in North America,'' said Stephenson. ``The bighorn occupy some of the most rugged terrain in California and for many they symbolize what's unique about the Sierra Nevada.''

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Photo:

(1 -- 2) Graduate student Cody Schroeder searches for endangered Sierra Nevada bighorn sheep, such as the one below, near Saddlebag Lake.

Bill Becher/Special to the Daily News