Wyoming Game and Fish Department biologist Gary Fralick measures a mule deer fawn as part of a study on fawn survival in the Wyoming Range mule deer herd. (Mark Gocke/Wyoming Game and Fish Department)

Kevin Montieth could tell from a distance that the deer were in bad shape.

Bitter cold and deep snow defined the winter of 2016-2017 in the Wyoming Range. The researcher knew many mule deer didn’t make it, and those that had endured would be on the edge of survival.

Even knowing what to expect, it was difficult to look at the starving deer in March. Defined bones jutted from beneath the animals’ winter coats. Some didn’t even stand up when the helicopter hovered above them.

“They were just surviving, or trying to,” said Montieth, a professor of natural resource science at the University of Wyoming.

Montieth knew the herd’s losses were severe. He was in the midst of a multi-year study that tracked does and fawns to learn what impacted the young animals’ survival, when the winter ravaged the herd. None of the 31 collared fawns alive in the fall survived. Only six of 32 died the previous winter. Thirty-seven percent of collared does died compared to about 5 percent to 8 percent in a normal year. Those that survived were barely holding on.

“It was like nothing I’ve probably ever fathomed seeing in my lifetime,” said Montieth, who’s worked with thousands of deer in his career. “They were in horrible shape.”

The winter hit the herd with freezing cold temperatures and deep snow that made food scarce and moving exhausting.

Yet the timing presented a rare opportunity for scientists to study how a herd recovers from such a harsh winter. Rarely does such a devastating event occur while a study is already underway. But because researchers have baseline data on the herd from previous years, and have animals collared for monitoring, the population drop represents a unique chance to explore one of the more vexing questions in deer science.

“It’s a once in probably many lifetimes opportunity to understand what the effects of a severe winter are,” Montieth said. “It’s an unbelievable opportunity to be poised and set up in the way that we are.”

The original study was slated to end after this summer, but Montieth has already extended it and hopes it will continue another two to three years. He’ll be able to see what happens to the herd and how quickly it recovers in the next few years and see the impact of a decimated deer population on the landscape. The deer decline will impact predators, but also forage growth, he said. Scientists can also examine survivors and try to learn why they lived when others died.

This winter was one of most severe in more than 30 years in the Wyoming Range, said Gary Fralick, a wildlife biologist with the Wyoming Game and Fish Department who is involved in the mule deer study. In severe winters about 18 percent to 25 percent of a herd dies, Fralick said. Fralick said he thinks this winter was so harsh the deer mortality rate is likely close to 25 percent in the Wyoming Range.

Herd recovery begins immediately, but it will be several years before there are 3-year-old bucks in the herd, Fralick said. The winter wiped out an entire age class, but also a substantial number of adults. Does that survived and were pregnant this spring were in poor condition, compared to previous years. The fetuses were also smaller this spring than normal, Montieth said.

The Wyoming Range deer herd is one of the region’s largest — before winter it was estimated to have 36,000 to 38,000 deer — and also one of the most studied. There are data from the 1980s on the herd, a gift to scientists trying to discern what is normal and what factors are impacting the population.

In the 1980s, the herd recovered quickly — within about three years after a large population loss, Fralick said. But the animals also had more fawns. Fawn survival has been declining since the mid-1980s and no one knows why. That’s one reason the initial fawn survival study is so important, Fralick said.

“At the basic fundamental level the population numbers grow when you add to the population,” he said. “If we aren’t able to add fawns and have them survive, the population can’t grow.”

There are many ways for fawns to die. Some are stillborn. Some drown. Some starve. Predators kill others, Fralick said.

Researchers have spent the last three years trying to learn more about fawn survival and recruitment in the Wyoming Range herd. Each March, scientists captured does, documented body condition and age and inserted a vaginal transmitter that alerted them when an animal gave birth, Montieth said. Researchers could then quickly find the doe and fawns to outfit the animals a GPS collar. Once collared researchers tracked the animals through the summer and winter. Researchers also monitored conditions like forage growth on winter range.

The study’s goal is to determine what factors impact population growth — predation, climate change, habitat loss, disease or something else — and understand why there aren’t more deer in the herd. What they learn will, ideally, lead to refined management tools and techniques that can help the animals thrive, Montieth said.

Montieth was surprised when the first year of the study revealed adenovirus had the greatest impact on fawn populations, not predators.

The virus can spread at feeding or baiting sites where animals gather. After the data showed adenovirus impact the population, Star Valley banned deer feeding. The next year, fewer fawns died from the virus, although it hasn’t been long enough, or the number large enough, to correlate the change in policy with animal health, he said.

“At least at a minimum we know this disease is out there and influencing our deer populations,” he said.

Biologist Gary Fralick covers a deer’s eyes to keep it calm while large carnivore biologist Ken Mills removes the hobbles prior to release. They’d captured the doe to measure and collect body condition information near Big Piney in March. (Mark Gocke/Wyoming Game and Fish Department)

Samantha Dwinnell, a research scientist with the University of Wyoming, started studying mule deer while working on her master’s degree. Her work considers how energy development changes deer behavior and how they use winter range. She’s been part of the fawn study since it began in March 2013.

In her years of deer study she’s learned and seen some amazing things, she said. Once, for example, she tracked a fawn as it migrated to summer range. The fawn’s mother had died, yet the young deer used a nearly identical route to the one it had traveled only a single time with its mother.

But too often, when researchers try to understand the population dynamics of large mammals, there isn’t enough long-term data on trends.

A chance to follow the herd after such a devastating winter is a rare and important opportunity.

“Inevitably mule deer populations do rebound,” she said. But how that rebound happens, and what factors impact it, are still unknown. “These next few years are really going to give us invaluable information, not just for the Wyoming Range mule deer, but mule deer throughout the West.”

Kelsey Dayton is a freelancer and the editor of Outdoors Unlimited, the magazine of the Outdoor Writers Association of America. She has worked as a reporter for the Gillette News-Record, Jackson Hole News&Guide and the Casper Star-Tribune. Contact Kelsey at kelseydayton@gmail.com. Follow Kelsey on Twitter at @Kelsey_Dayton