A contagious pneumonia shows no sign of retreat five years after it killed 75 percent of the bighorn sheep in Custer State Park. The spring lambing season has produced no offspring since then and an aging herd once numbering more than 200 is down to 28 animals.
Bighorns elsewhere in the Black Hills appear healthy, although there's always a chance the herds could mingle and the disease could spread.
For now, it's wait and see, said Gary Brundige, the resource program manager and former wildlife biologist in the 71,000-acre park in the Black Hills.
"In other herds that have had these pneumonia outbreaks in the West it takes a number of years for the herd to start producing again," he said. "The flip side is that in Hell Canyon on the Idaho-Oregon border the sheep herd that had a big die off is going into its 11th year with virtually no production. So we're five years in and in another five or six years we may not have any sheep left."
The Custer Park bighorns began dying in early 2005, possibly after a ram picked up the disease from a domestic sheep herd outside the park. The bighorn herd dropped from 200 animals to about 48 in spring 2005 and is down to 28 now.
The surviving bighorns appear resistant to the disease, but apparently can pass it on to others. Lambs born in late May and early June live for a few weeks and then die, said Brundige.
"So the thought is that once these lambs get through their first colostrum immunity that they're actually developing the disease from contact with the adults."
Other Western states report the disease. More than 400 bighorn sheep in Nevada, Montana, Utah and Washington have died or been killed by wildlife officials this winter.
There are two other main bighorn herds in the Black Hills: about 100 head in one grouping, and another of 250 head broken into three smaller subgroups.
There has been some movement between those herds and the Custer Park herd, raising the possibility of spreading the disease outside the park, said John Kanta, regional wildlife manager for the GF&P in Rapid City.
"Presently, with so few sheep in Custer State Park, the interaction is minimal, but it's something on our mind," he said.
Bighorn hunting in Custer State Park has been suspended since the die off, but the state proposes offering five hunting licenses for bighorns elsewhere in the Black Hills this year. Five licenses costing $255 each were issued last year through a drawing. A hunter can receive only one license in their lifetime.
Brundige said lamb survival this spring could be a sign that the disease has run its course. Then the park could transplant sheep from another state or Canada to grow the herd again.
A last option would be to kill what's left of the herd and start over.
"It's something we have talked about as an option but there are a number of factors that need to be determined whether that's even a viable direction to go. It's certainly not imminent," Brundige said.