BEND — There's a healthy, growing population of between 350 and 400 bighorn sheep in and around the Lower Deschutes River Canyon.

BEND — There's a healthy, growing population of between 350 and 400 bighorn sheep in and around the Lower Deschutes River Canyon.

But to keep an eye on the herds and make sure the population stays strong, the Oregon Department of Fish and Wildlife is launching a study to determine how these sheep die.

"At some point in time, we are going to have that population decline," says Keith Kohl, district wildlife biologist for Fish and Wildlife's mid-Columbia district. "We want to get ahead of that and see if there's anything we can help out with."

So starting this month, the agency is using helicopters and nets to capture and collar 35 of the California bighorn sheep that live along the river. The collars will have a mortality sensor on them, Kohl says, which works by beeping faster if the tag hasn't moved for a certain period of time.

The idea is to then find the sheep — some of the tags have Global Positioning System components to them, others are radio transmitters — and determine why they died. More cougars are prowling the area, Kohl says, so he is hoping to know if they have an effect in coming years.

Most of the populations that have been introduced in Oregon — if they are in good habitat — will expand and do well, he says. At some point they hit some environmental constraint or habitat limitation and their numbers start to decline or level off. For now, though, the population along the Lower Deschutes is doing well, he says.

When white settlers came to Central and Eastern Oregon, there were more bighorn sheep than mule deer, he says. But hunting and diseases carried by domesticated sheep wiped out California bighorn sheep in Oregon by 1915, and Rocky Mountain bighorns by 1945, according to the state's management plan.

Efforts to bring the California bighorns back to the state started around 1954 in the Hart Mountain area in southeast Oregon.

"Since that time we've been trying to reintroduce bighorn sheep back into their native habitat," Kohl says.

Sheep were reintroduced into the Lower Deschutes River Canyon in 1993. Sixty-five sheep were released in the lower river area, according to the management plan, and in the first 10 years the population grew to 200 animals.

Now, between 350 and 400 sheep inhabit the area, Kohl says, with more than 3,000 California bighorn sheep statewide.

The animals have lots of appropriate habitat, mild winters and grasses to eat, as well as few predators. The population along the Deschutes is often used as a source for animals that are trapped and moved to start new herds elsewhere, he says.

But bighorn populations in the Hart Mountain and Steens Mountain areas haven't been doing as well, he says. While the Fish and Wildlife department is doing studies to look at why these sheep are dying, Kohl says he also wants to get in front of the problems and see whether there are similar findings on the Deschutes.

"The longer that we can keep this population good, the more sheep that we will have to fill in suitable habitat in this state and others," Kohl says.

The state offers only about 90 hunting tags for the big game animal each year, Kohl says, and the tags are once-in-a-lifetime deals. They are also in demand — the state auctions one tag and raffles off another, which together can bring in $120,000 or more.

The Deschutes bighorn study is being supported with grants from the Oregon Hunters Association, and the Oregon and the Minnesota-Wisconsin chapters of the Foundation for North American Wild Sheep.

Duane Dungannon of Talent, state coordinator for the Medford-based OHA, says this is "a priority project because it's one where we can make a huge difference."

Because the range and population are small, different projects can have an impact, he says.

But the bighorn sheep are "high-maintenance animals," he says, and can't just be released into the wild and left alone. Studying healthy herds and unhealthy herds could help determine what factors lead to their success and help keep the populations strong.

"It's a pretty special species," Dungannon says, "and I think that to a lot of us, whether you're a hunter or a wildlife enthusiast or both, it's a pretty magnificent animal."