The Cinnabar herd of bighorn sheep that lives just north of Yellowstone National Park has been slow to recover from an outbreak of pneumonia in 2014.
“During the spring survey the numbers weren’t bad,” said Karen Loveless, a Fish, Wildlife and Parks biologist in Livingston. “But the lamb recruitment is not great. And we’re seeing that again this year. That’s discouraging.”
The outbreak of disease initially resulted in the deaths of 34 sheep out of a herd of 89, many of them rams. Because of the deaths FWP closed Hunting District 305 to bighorn sheep hunting.
“I’d sure like to open it,” Loveless said. “But I’ll wait and see what we get this spring. If ram numbers remain low … I don’t want to offer a tag for hunters if it’s unlikely to be filled.”
So far the disease outbreak seems to be isolated to the Cinnabar herd, which lives on the west side of the Yellowstone River in the Gardiner Basin. Bighorns on the east side of the river, the Corwin Springs herd, seem to be doing fine. Likewise, bighorn sheep numbers in nearby Yellowstone National Park, just south of Gardiner, are OK.
Loveless said some of the sheep from the uninfected herds may move into the Cinnabar habitat to help repopulate the herd.
“We know rams certainly move around during the rut,” she said.
The continued scarcity of lambs in the Cinnabar herd is not unusual. Bighorn sheep in other areas have suffered from an inability to rebuild their numbers after a pneumonia outbreak. The bacteria seems to persist in some ewes and may infect their milk, killing weak newborns.
Although there are plenty of predators in the area, including mountain lions, Loveless said their numbers haven’t increased so they aren’t likely to be a factor in the lack of lambs.
Downriver farther, the Point of Rocks bighorn herd had a pneumonia outbreak, yet still had good lamb recruitment, but then got sick again. The sheep don’t have immunity to a bacteria carried by domestic sheep. It’s believed that when bighorn rams wander and come in contact with domestic sheep they may carry the pneumonia back to infect their herds.
A bighorn sheep herd in the Tendoy Mountains of southwestern Montana suffered continued outbreaks of pneumonia. Despite several attempts to rebuild the herd with bighorns captured and transplanted to the Tendoys, the group never rebounded. So in 2015 FWP enlisted hunters to help remove all of the animals. Most were killed, leaving FWP to harvest the few remaining that hunters were unsuccessful in taking.
FWP plans to repopulate the Tendoy-area herd with bighorns that are free of disease in hopes that the animals will thrive once again.
Loveless is optimistic that the outbreak in the Gardiner Basin won’t spread to surrounding herds, but more information will be available after FWP flies the region in March to count wildlife.
The Gardiner Basin is steeped in bighorn sheep history. Evidence of ancient sheep traps built by early Americans has been found in the rocky cliffs near Gardiner along the Yellowstone River. Surrounding peaks have names like Big Horn, Ramshorn and two versions of Sheep Mountain.
Unlike some other places in Montana, the Gardiner Basin sheep are native herds.