BOISE - The Sheep Mountain herd of bighorns on the Idaho-Oregon border once contained nearly 90 members until the arrival of bacterial pneumonia. Now, biologists plan to use a helicopter this week to capture the three known survivors in Idaho and search for others that might be on the Oregon side of the Snake River in the upper end of Hells Canyon.

"Nobody has seen a sheep on the Oregon side in a long time," said Brian Ratliff, a wildlife biologist with the Oregon Department of Fish and Wildlife.

The captured bighorns will be sent to a research facility at South Dakota State University as part of a three-year study involving about 40 wild sheep from the Northwest as well as some from South Dakota.

Scientists hope to find a way to stop the spread of disease that continues to limit the success of bighorn herds throughout the West.

Jonathan Jenks, distinguished professor of Natural Resource Management at South Dakota State University, said the three sheep are a significant addition to the study because they carry a unique strain of mycoplasma, an infective pathogen. "We're hopeful we're going to have some really interesting results that are going to improve bighorn sheep management throughout western North America," he said.

The 40 sheep all come from wild Rocky Mountain bighorn herds experiencing die-offs, Jenks said. Scientists say herds start having problems when adults become infected. Many die, but some survive only to pass the disease to lambs, which nearly always die.

The goal among researches is to try to find an easy way to identify "super shedders" that keep the pathogen present in a herd and prevent any lambs from surviving, eventually causing the herd to die off.

But Jenks said the issue is complicated because some bighorns are only intermittent shedders and others test negative. Experiments so far, he said, have shown that lambs born to super shedders don't survive.

The goal at the end of the study is to return healthy sheep to the wild, he said.

The Sheep Mountain herd is emblematic of the problems faced by bighorn sheep managers in the West. Bighorns were native in Hells Canyon before being extirpated in the 1940s because of what experts say was unregulated hunting and the introduction of diseases from domestic sheep.

Wildlife managers have been working in many states to reintroduce bighorns into native habitat.

Oregon officials started the Sheep Mountain herd with transplants of 30 bighorns from Colorado in 1990. The herd was bolstered with 10 more in 1995 from Alberta, Canada, and another two from an Oregon herd. The herd grew to nearly 90 by 1999.

But a nearby bighorn herd called the Leap Creek herd became infected with bacterial pneumonia and spread the disease to the Sheep Mountain herd, Ratliff said. The Leap Creek herd died out about a decade ago, Ratliff said, and now the Sheep Mountain herd is nearing the end.

"It's a rough thing," said Regan Berkley, a wildlife manager with Idaho Fish and Game who has watched the herd decline. "Bighorns are one of the iconic animals of the West."

Oregon officials are also concerned about the nearby Lookout Mountain herd that has remained disease free and is separated from the Sheep Mountain herd by the Powder River arm of Brownlee Reservoir. "All it would take to wipe out that Lookout Mountain herd is for a ram to swim across," he said.

For that reason, Berkley said, officials there have offered hunters more opportunities to bag a bighorn ram to reduce the chance of one wandering away. Still, it's tough to get a tag, Ratliff noting that 783 hunters applied for one bighorn tag for the Lookout Mountain herd.

Another option is to outbid everybody for an auction tag. The Oregon bighorn auction tag sold for $160,000 earlier this month. In Idaho, a similar auction tag went for $100,000.

Bighorns are also popular, Ratliff said, among wildlife viewers, photographers, and some people who just like knowing there are places wild enough for bighorns.

The Oregon agency doesn't have any current plans to transplant bighorns to replace the Sheep Mountain herd because of a private landowner in Idaho who has domestic sheep that can transmit deadly diseases to bighorns, he said.