Nature will have its way with the remaining Rock Creek bighorn sheep battling a pneumonia outbreak.

"We didn’t see any clear way to distinguish which ones to save and which ones to remove," said Mike Thompson, wildlife manager for the Department of Fish, Wildlife and Parks. "It appears to be spread through whole herd we were able to sample. That solidified our decision to let it run its course."

Biologists flew a helicopter survey of the drainage last week. In the open country of the upper Rock Creek habitat, about 45 percent of the herd were coughing and showing other symptoms of the usually fatal disease. There have been about 340 bighorns in that area.

The lower part of the drainage had about 200 bighorns. Biologists have killed and tested 13 sheep, and all were infected. The disease is extremely contagious in wild sheep populations, and kills between seven and nine of every 10 victims.

Because sheep in the upper drainage mingle in large herds, and those in the lower drainage live in steep, cliffy terrain, Thompson said there were no good options for culling the sick animals.

That’s different from the outbreak of pneumonia in bighorns above West Riverside east of Missoula. There, FWP shooters killed 95 sick sheep in the mountains north of the Blackfoot River in hopes of protecting more isolated bands farther in the Rattlesnake Wilderness Area. The area held about 160 bighorns before the disease appeared in early January.

A similar cull in the mountains south of Darby in November appears to have protected some sheep there. Recent aerial surveys showed 69 healthy animals after FWP killed 77 infected ones.

This weekend, FWP biologists hope to capture 40 bighorns from Wild Horse Island in Flathead Lake. The herd there has more than 200 animals. In January 2008, a similar effort collected 38 sheep and relocated them to the Kootenai Falls Wildlife Management Area.

If this project goes as planned, 20 sheep would go to the East Fork of the Bull River in Sanders County, with the remainder going to Kootenai Falls.

FWP Region 1 spokesman John Fraley said veterinarians would monitor the effort and check for any disease symptoms. So far, the Wild Horse Island herd has shown no indications of disease.

Details from all the disease outbreaks this winter are being compiled for a report that’s due around next August, Thompson said. It will include lab analyses of the dead animals and the types of pneumonia that killed them, effectiveness of the cull efforts, and population surveys.

Reporter Rob Chaney can be reached at 523-5282 or at rchaney@missoulian.com.