HAMILTON - State wildlife officials have confirmed that bighorn sheep from the East Fork Bitterroot herd south of Darby recently died of pneumonia.
"It's really bad news," said Craig Jourdonnais, Bitterroot-based biologist for Montana Fish, Wildlife and Parks. "There's been a history of herds losing 60 to 70 percent of their numbers in a very short period of time when something like this hits."
The nearly always fatal respiratory disease was first suspected after hunters reported seeing coughing bighorn sheep near the East Fork last Sunday.
Jourdonnais said he found two dead sheep on the East Fork Road. The two rams - an 8 1/2- and 4 1/2-year-old - tested positive for pneumonia at FWP's wildlife laboratory in Bozeman Tuesday.
"Both had a very advanced case of pneumonia," Jourdonnais said. "The vet had to almost peel their lungs away from the rib cage."
Jennifer Ramsey, FWP's wildlife veterinarian in Bozeman said the state will attempt to cull more sheep from the herd over the coming weeks.
"Our top priority is to remove sick and dying animals and to collect biological samples for testing," she said. "Additional laboratory test will determine the specific strain of the bacteria, and removing sick animals could help slow the spread of the disease."
Jourdonnais said he will shoot three or four sheep that are exhibiting signs of the disease on Wednesday for further testing.
"Typically we don't have a lot of options in cases like this," Jourdonnais said. "It tends to have to run its course."
Once bighorns contract pneumonia, they die within a few days. There are no known vaccines to prevent pneumonia in wild sheep.
The East Fork bighorn sheep herd was established in 1972 when 35 sheep were transplanted there.
Jourdonnais said he counted 185 sheep last year during an aerial survey last March.
"They all looked vibrant and healthy at that time," he said.
The herd has been the source of some "tremendous rams" over the past few years, with a few close to record book size, Jourdonnais said.
"They are a real asset to the Bitterroot," he said. "The East Fork herd is pretty well known."
In extreme cases, pneumonia-related outbreaks among bighorn sheep can result in herd "die-offs." The most recent case in Montana occurred in the Elkhorn Mountains near Helena. Similar die-offs happened in the Highland Mountains in 1995 and in the Tendoy Mountains in 1993.
Jourdonnais said there's no evidence the disease originated in domestic sheep or goats.
"We do have a few isolated herds of sheep and goats nearby, but there is absolutely no knowledge that has anything to do with what's going on here," he said.
It is illegal to possess a bighorn sheep head picked up in the wild. Anyone who finds a dead or sick bighorn sheep is asked to call FWP in Missoula at 542-5500.