Pneumonia kills 37 bighorn sheep on bison range

During the past two months, wildlife officials at the National Bison Range have documented the deaths of 37 bighorn sheep due to a pneumonia outbreak.

Known mainly for its namesake bison, the 18,766-acre wildlife refuge near Moiese also hosts several other large wildlife populations, including a herd of sheep that numbered about 175 prior to the recent mortalities.

The first dead sheep was found in early September, said Amy Lisk, a wildlife biologist at the bison range. The most recent carcass was discovered last weekend. It’s the first disease outbreak known to have occurred in the refuge’s sheep population, Lisk added.

Bighorn sheep die-offs have been documented in other parts of the state — one of the most recent being earlier this year when a pneumonia outbreak claimed 34 sheep from a herd near Gardiner.

“While I don’t know the extent of the exposure, based on the behavior of this population, more have likely been exposed,” Lisk said. “The extent and duration is yet to be determined. We don’t know how long we will continue to see mortality from respiratory illness or what the final population to succumb will be.”

The respiratory illness was first detected in August, and Lisk said symptoms typically appear 40 to 60 days after the exposure. While she has taken samples from the dead sheep, Lisk has not yet identified the specific disease causing the pneumonia outbreak.

Wildlife biologists with the U.S. Fish and Wildlife Service, Montana Fish, Wildlife and Parks and the Montana Conservation Science Center are working together to find out what actions, if any, can be taken.

“We’ll just let the illness run its course and when we know how the problem started, what the problem actually is and can pinpoint things more precisely, then we can start to outline what our options are,” she said. “You could lose 10 percent to 90 percent of your population, and at this point we can’t speculate on what that would be here.”

Reporter Sam Wilson can be reached at 758-4407 or by email at swilson@dailyinterlake.com.