Enigmatic of the American West and an enduring symbol of the region’s spirit, bison are known for their unyielding toughness. This has allowed them to make a life in our country’s farthest reaches and live well into their 20s.
“The typical annual survival rate is high 90s, like 98%,” said Rusty Robinson, the Utah Department of Wildlife Resources Once-in-a-Lifetime Species Coordinator.
He says with such a high annual survival rate, losing one bison seems odd.
But this July, many more than one bison in Utah’s Book Cliffs suddenly started dying.
“We estimate that we lost about 40% of the population in about 6 days,” Robinson explained. “It was really intense. We had about 150 adults before the die-off, and when the dust settled, we were at about 90 adults.”
So, what’s causing it? State veterinarian Ginger Stout collected samples from deceased bison, and the findings are surprising.
“The main cause of death was pneumonia,” Stout said. “But they're two different pathogens that were found causing the pneumonia.”
Stout explains that an introduced virus, in conjunction with a bacterial infection, acted as a double whammy to bison that were already dealing with environmental stressors.
“They have found that wildfire smoke can actually reduce the ability to move pathogens out of the upper airway,” Stout explained, pointing to this year’s hot summer as one factor that impacted bison health. “Stress is another factor, so heat stress and water stress. So, with the drought, that's also another thing that can help the bacteria to kind of take hold and cause death.”
Stout says spotting infected bison isn’t difficult.
“Those bison had snotty noses, trouble breathing, just really lethargic, and not able to walk around very well,” Stout said.
While the bison are no longer dying, Stout says there are still some unresolved questions.
“I think the biggest unanswered question is where it came from. Previously, the virus we identified wasn't in the herd,” Stout explained. “We're also wondering, what the sequencing is of the bacteria that actually killed the animals. […] So hopefully, we'll understand the genetics of the bacteria and understand why it was so severe and killed off so many.”
The bison die-off also leaves unanswered questions for hunters. A bison tag is a once in a lifetime opportunity in the Utah, sometimes taking over 20 years to get picked in the state's draw system. In considering both bison and the hunters, managers like Rusty Robinson tried to strike the balance that would benefit both.
“Before the die-off, we were at about 150 adults, and the plan was to slowly grow it up to that 250 mark” Robinson said. “Now that we've been knocked so far down, it's unlikely that we'll hunt cows for a few years at all.”
Robinson says the immediate solution, however, is not so black and white.
“There's fairness, and then there's being accommodating, and we tried to accomplish both,” Robinson explained. “You know, it's probably fair to just cancel the hunt and give people their points back, but we also wanted to try to be accommodating.”
To do so, Robinson and the Department of Wildlife Resources came up with a dynamic solution that offers hunters more options. This involves hunting cows in a different unit to decrease pressure on an already struggling herd.
“You know, there's no perfect answer,” Robinson explained. “There's no solution that's going to be perfect for everyone in this scenario.”
Robinson and Stout are hopeful that the worst is behind us, and the Department of Wildlife Resources can begin to manage the herd back up to previous numbers.
People can do their part by keeping a safe distance from bison. This will help avoid adding any unnecessary stress on the symbolic Western megafauna.
