Elk NetworkStudy: Harsh Wyoming Winter Had Devastating Impact on Mule Deer

General | October 19, 2023

Below is a news release from the Wyoming Game & Fish Department.

A five-year, groundbreaking project by the Wyoming Game and Fish Department to study mule deer in the Cowboy State is underway. This project, which started in late 2022, takes a deeper data dive by researching six areas considered critical for mule deer management: abundance, composition, data management, survival, herd health and harvest management. One of the primary research questions the project hopes to address is abundance — how many individual mule deer are in each of the state’s herds.

From late 2022 through early 2023, 1,112 collars were placed on mule deer from five focal herds around the state. In each herd, 80 does, 30 bucks and 100 juveniles — animals at least 6 months old — were collared.

Focal herds in this project include: Wyoming Range, Laramie Mountains, North Bighorn, Sweetwater and Upper Shoshone. These focal herds are located in different parts of the state and feature many unique characteristics, which may allow Game and Fish to understand why some herds perform better than others. Additional collaring efforts will be made in November so robust data can continue to be collected.

Winter mortality varied across the state
The winter of 2022-23 will go down as one of the more significant and devastating to mule deer in Wyoming history, especially in central and western Wyoming. Sustained snow, wind and cold temperatures took its toll. For example, in the Wyoming Range herd all 100 juveniles collared for this project died during the winter.

“Hopefully it will be a while before we see a winter like this again,” said Gary Fralick, Game and Fish biologist in the Jackson Region who has done extensive work and research on mule deer in the Wyoming Range throughout his 30-plus years with the department. “It’s going to take a long time for this deer herd to bounce back.”

Despite the harsh winter and mule deer deaths in some parts of Wyoming, other focal herds came out of the winter quite well.

Sam Stephens, Game and Fish biologist based in Greybull who works with the west side of the North Bighorn herd, said despite lots of snow and numerous below-zero cold snaps, mule deer in his area made it through the winter well.

“We had 89 percent of collared does survive, and juveniles fared relatively well at around 81 percent,” he said.

Zach Turnbull, Game and Fish biologist who works with the North Bighorn herd in the Buffalo and Sheridan areas, said the winter was one of the most severe in Johnson and Sheridan counties since the 1980s. However, mortality for juveniles was about 35 percent and around 12 to 15 percent for bucks and does.

“Not great, but not horrible,” Turnbull said.

The Sweetwater herd unit is in central Wyoming surrounding Jeffrey City. Mortality of juveniles over the winter was more than 60 percent. However, doe and buck mortality rates were 20 and 30 percent range, respectively. If anything, the 2022-23 winter wasn’t the same for all of Wyoming and its mule deer.

“Being able to see some of that statewide variation was super interesting,” said Embere Hall, Game and Fish science, research and analytical support unit supervisor and lead on this project. “I think it’s easy to wring our hands and say ‘winter was terrible and we’re losing all the deer.’ Actually, that’s not true. We lost a lot on the western side of the state. That population really took a hit. The eastern part of the state wasn’t that bad.”

What we’re learning
Keaton Weber, Game and Fish biologist in Wheatland, said the Mule Deer Monitoring Project is the first time Game and Fish conducted a collaring study on the Laramie Mountains herd. Weber also said despite tough winter conditions, 70 percent of juveniles, 79 percent of does and 86 percent of bucks collared for this project survived the winter.

“Survival data is some of the best information we can learn, and to have that after a harsh winter is really beneficial to us to estimate abundance and also understand how survival varies in harsh winters and mild winters,” Weber said.

Since no extensive studies have been done on the Laramie Mountains herd, any information is valuable. Weber added this herd isn’t as migratory as others around the state, but there have been some surprising movements of deer so far.

Another positive result for Weber has been with the public. Laramie Mountains mule deer herd is predominantly private land. Weber said landowners have shown great cooperation in granting Game and Fish access to capture deer and retrieve collars.

“We’re fortunate to have a lot of landowners that support the department, support this project and want to learn more about the Laramie Mountains mule deer herd,” Weber said. “We’re forever grateful to them for access to their properties to learn more about this herd and why it’s been struggling. We hope to continue to have that support throughout this project.”

Tony Mong, Game and Fish wildlife biologist in Cody, said a lot has been learned about the Upper Shoshone herd in the first year of the project.

“It has shown us we weren’t catching all the areas mule deer use or all the different routes or pathways they’re taking to get there,” Mong said. “It is some really cool stuff.”

Mong said mule deer in the Upper Shoshone herd move a lot, and as of mid-July there were deer from this herd in the Jackson and Lander regions. Mule deer in this herd are part of a diverse area of land that ranges from remote wilderness to highly developed private land. And some of these deer spend a lot of their time in Yellowstone and Grand Teton national parks.

“This herd highlights the importance of collaboration and cooperation when it comes to management across every entity that has anything to do with land in Wyoming,” Mong added.

Collaborative effort
The University of Wyoming and the Wyoming State Veterinary Lab are key partners in the Mule Deer Monitoring Project. UW is processing all the data from collars, in collaboration with the department’s science, research and analytical support unit.

Focal herd managers receive real-time data and a report each Monday highlighting current survival, the number of mortalities in the past week and a map of recent movements. In addition, managers and other Game and Fish decision-makers can log in to a dashboard that shows real-time survival estimates and movements. Quick access to the data was especially important during conversations with the public this winter, as well as to the department’s season-setting process.

What’s next
Collaring more deer to keep the sample size of each herd at or as close to 80 bucks, 30 does and 100 juveniles is a priority. Data collection and analysis, along with lab work will continue.

Hunter harvest surveys also will provide important information. Game and Fish conducts surveys of hunters each year to determine how many animals were harvested from each hunt area, how satisfied hunters were with their experience and how many days it took to harvest an animal. The surveys are a critical tool in setting seasons and allocating licenses.

Since the project is just short of one year in a five-year timeframe, there are still a lot of unknowns. It’s too early to come to many conclusions, but optimism is high.

“This is just the tip of the iceberg of what we’re going to learn,” Mong said. “This is a catalyst for learning so much more about our mule deer. I feel in five years we’ll be able to make much better management decisions and have the data to back that up.”

(Photo credit: Wyoming Game & Fish Department)