A black-and-white helicopter flew over the snowy hills of the Gros Ventre Wilderness in Teton County as researchers like Alyson Courtemanch were trapping bighorn sheep on a freezing winter morning.
“At this time of year, they should be in the best physical condition after the summer and fall,” Courtemarch said.
Courtemanch is with the Wyoming Game & Fish Department who are monitoring Jackson’s wild herd of sheep for pneumonia, a disease that has killed bighorn sheep across the west and can destroy entire ecosystems. While the researchers weren’t sounding alarms, they were concerned that Jackson’s group was soon doomed to another death.
A female bighorn sheep takes off in the snow, after researchers captured her by helicopter and monitored her health. (Emily Cohen/Khol)
Pneumonia pathogens, Courtemarch said, already live within the herd.
“They’re just lying dormant in their bodies,” she said. “[But] something can trigger these pathogens to take over.
Up in the air
To assess the health of the herd, helicopter pilots tracked nearby sheep, which already had GPS collars. The crew brought down a net and a member called the “robber” jumped out of the helicopter, tying the bighorn’s legs together and blindfolding him.
Courtemanch said this kept the sheep relatively calm as it dangled on a rope below the helicopter. It was then flown back to researchers in nearby hills, who took measurements before releasing it into the wild.
“So, we’re looking at the amount of fat they have on their body to get a sense of how well they did over the summer,” Courtemarch said.
Biologists collect this data before and after winter to see how habitat is affecting Jackson’s herd.
One crew member, Ben Regan, held back one of the squirming ewes. He weighed her first and then carried her onto a mat to take more measurements.
“We start by taking the temperature,” Regan said. “That way we can see if the sheep is warm, if the tracking time might have been a bit longer.”
As the helicopter flew overhead, Regan used an ultrasound to measure the fat on the sheep. Then, she checked if she was nursing, to see if she had a lamb. Then came the tonsil and nasal swabs.
“We’re basically able to look at what pathogens they have that could lead to pneumonia, which is a big disease that affects wild sheep in the West,” Regan said.
“High Levels of Abundance”
There were an estimated two million bighorn sheep in North America. According to the National Wildlife Federation, fewer than 85,000 now remain. Courtemanch said this was largely due to pneumonia, which was introduced by domesticated sheep.
Researchers at the University of Wyoming have been studying the disease in sheep for nearly a decade. Kevin Monteith, who leads these studies, said pneumonia deaths occur when the population reaches its carrying capacity in the local habitat.
Crew members hold the sheep’s mouth open to take tonsil swabs. (Emily Cohen/Khol)
Recently, the herd numbered more than 500 sheep, a maximum for the group.
“When we reach those high levels of abundance, it can be related to animals competing for food, which means poor nutritional status, which means an extra layer that they are struggling with when you add their efforts to fight pathogens to the same time,” Monteith said.
Ppneumonia hit the herd in the early 2000s and killed about 70% of the sheep. Another death that was about a decade ago, in 2012.
The researchers said they fear the herd is due for another.
Sheep hunting
Faced with a potential kill, the Game & Fish department recently issued limited hunting permits for female sheep for the first time.
The researchers said they expect that by reducing population the herd will become healthier with more food in circulation and be able to fight off pneumonia.
“This population is very large right now,” Monteith said. “It’s close to that historic abundance where we often see those incidents, and so we’ve waited, wondering if we’ll see [a die-off].”
The department has allowed 16 sheep to be hunted, but less than half of those were actually harvested last year. Monteith said it’s still too early to know if herd reductions have had any impact.
“The reality is, it just takes time,” Monteith said.
Upon Jackson’s recent capture, the researchers said they say red flags. More lambs died of pneumonia and the ewes had slightly lower levels of body fat, which has been declining in recent years.
Another pack in trouble
Regardless, this herd is thriving compared to another group of bighorn sheep crossing nearby bluffs in the Tetons.
Those sheep have received more attention in recent years as development limits migration patterns, which some environmentalists say is threatening their health.
Courtemanch, with the Game & Fish department, manages both the Jackson and Teton herds.
“You have a herd that is almost doing too well that we need to reduce population numbers, and then we have another herd like the Tetons that is struggling and not doing very well,” he said. “So, we do very different management depending on what’s going on with that specific population.”
The researchers will reassess the Jackson herd population in February and then decide whether to issue even more hunting permits.
Researchers carry a female sheep in a tarp and prepare to release her. (Emily Cohen/Khol)
But, on that cold winter day, the captured bighorn sheep return to the wild.
“We finished sampling a couple of sheep,” Courtemarch said. “So, we’re about to release them back into the hill.”
The biologists took a female sheep to a nearby hill, removed her blindfold and untied her legs. Within seconds she was off into the snow, ready for the winter ahead.