State wildlife officials confirmed today that a significant bighorn sheep die-off is underway in the East Fork Bitterroot herd, south of Darby, where pneumonia was first detected in two bighorn on November 22nd.
As of Sunday afternoon, Montana Fish, Wildlife & Parks (FWP) biologists had collected and delivered the carcasses of nineteen sheep to FWP’s wildlife lab in Bozeman for testing, with another eight expected to arrive today. The sheep examined through Sunday included ten males and seven females, and ranged in age from lambs to a seven-year-old.
“All nineteen sheep from the East Fork showed evidence of pneumonia,” said Jennifer Ramsey, FWP wildlife veterinarian. “All but three had severe pneumonia with extensive production of fibrin within the chest cavity. The three animals with less severe disease had very congested lungs. Most likely, these three animals were in an earlier stage of disease than the more severe cases.”
Samples of lung tissue and other biological samples will be sent to a laboratory for culture to try to determine what pathogens are involved in the pneumonia, Ramsey said.
Mortalities documented to date amount to upwards of ten percent of the East Fork herd, and FWP expects more sheep to die in the coming days and weeks before the disease runs its course.
“Many of the sheep we’re finding now are extremely lethargic,” said Craig Jourdonnais, FWP biologist in Hamilton, who leads the monitoring and collection efforts. “They move a short distance and then bed down right away. I suspect we’ll find advanced cases of pneumonia in these sheep within a very few days.”
The nearly always-fatal respiratory disease was first suspected when hunters at the Darby Check Station reported seeing coughing bighorn sheep near the East Fork on Sunday, Nov. 22.
Once bighorns contract pneumonia, however, they die within a few days. There are no known vaccines to prevent pneumonia in wild sheep.
“This appeared to happen very quickly,” noted Jourdonnais. “I’ve been classifying bighorns from the ground off and on through October and they looked healthy and vigorous then.” Since word of the pneumonia outbreak was made public last week, FWP has received similar reports from others, including a state wildlife manager from Idaho, who had been watching bighorns of the East Fork herd as recently as two weeks ago, with no signs of coughing or other symptoms of pneumonia.
FWP officials declined to predict the eventual extent of the die-off, but cautioned that 50-70 percent of a bighorn herd may be lost in extreme cases, and lamb survival may be suppressed for an extended period of years afterward.
“We really appreciate the reports of hunters who helped us detect this outbreak,” Jourdonnais said. “If early detection and rapid removal of diseased carcasses from the field have helped contain this outbreak in any way, our public deserves a lot of the credit.”
Hunters, hikers, cross-country skiers, snowmobile riders, and others are reminded that it is illegal to possess a bighorn sheep head picked up in the wild. Anyone who finds dead or sick bighorn sheep is asked to call FWP in Missoula at 406-542-5500.