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North Dakota’s bighorn restoration program has suffered another setback as at least 20 bighorn sheep have died after coming into contact with domestic livestock.

Since last month, at least 20 of North Dakota’s prized bighorn sheep have died of pneumonia in the northern Badlands habitat. Tests indicated that the disease came from contact with domestic sheep. It is spreading among the several bighorn groups in what biologist Brett Wiedmann calls “the hub of the wheel” for bighorns.

Of the dead bighorns, 14 were among a group of two dozen transplanted to the area last February from a pristine location in the northern Rocky Mountain region of Alberta. These bighorns may have been particularly vulnerable to disease as they had never had come into contact with domestic sheep.

“It went from being a great project to a nightmare. I hate to see it,” Wiedmann told the Bismarck Tribune. “It’s terrible, the worst thing in the world. They are such a magnificent animal.”

While there is no way to precisely count the mortality rate, Weidmann can confirm that at least 20 bighorns are dead. The sheep had been fitted with radio collars designed to emit a mortality signal. Wiedmann made his way out to each corpse after hearing the dreaded beeping noise and took field samples for the veterinarian. He noted that one of the dead bighorns was a state-record ram with the largest horns he had ever seen.

The surviving Alberta bighorns are also fitted with collars, as are another 51 bighorns in the same area. There are 350 bighorns in western North Dakota, however, the majority of which are not wearing collars and may have succumbed to illness.

“How many? It’s still playing out. We really won’t know until next year,” Wiedmann told the Dickinson Press. Mortality could vary widely though, from a low of 25% to a high of 95%.

Bighorn sheep are highly susceptible to disease transmitted from domestic animals.

"They have no resistance to the bacteria carried by domestic sheep. It's deadly," Wiedmann remarked.

Officials believe the most likely scenario is that a bighorn came into contact with domestic sheep and brought the pathogen back into the wild.

Wiedmann reports that he saw 35 domestic sheep this May while flying a mule deer survey. He immediately cautioned the owner to isolate bighorns from the domestic sheep.

“The owner felt terrible. He had no idea. He said they’d be loaded up that day and they were gone,” Wiedmann recalls.

At that point, it was a waiting game. As it turned out, it took until early August when the first mortality signals began coming in.

“The Alberta bighorns look perfectly health and then they’re dead,” he laments.  

Dan Grove, a wildlife veterinarian with the agency, says that a death from pneumonia means the animal drowns from fluid buildup in its lungs.

"It's pretty gruesome," he explains.

There was a pneumonia outbreak this past summer in Montana, but it pales in comparison to the devastation in North Dakota. Grove said it's the most severe bighorn die-off he's ever seen.

"We're trying to be optimistic. The mortality has slowed down, but to think this is completely over would be foolish on our part," Grove warns.

Wiedmann adds that this year's bighorn sheep hunting season, which is scheduled to open on October 31, will not be impacted. Only five licenses were issued, including one at an auction that raised $70,000.

Bighorn sheep are native to North Dakota, but the state’s population was wiped out in the early 1900s because of over-hunting and disease. Bighorns would not inhabit the state again until the mid-1950s, when animals from British Columbia were transplanted to the Badlands. Since then, the state has carefully transplanted sheep from other areas, including California and Montana, in hopes of restoring a self-sustaining herd in the state.

Despite continuing efforts, North Dakota Game and Fish officials have experienced a number of disappointments and setbacks. Yet they have persisted, forging ahead in an attempt to restore and rebuild the state’s bighorn population.

The agency will have to make key decisions on whether to continue the program or not.