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A new study from ÈÕ±¾avÊÓƵ is working to better understand juvenile survival rates for mule and white-tailed deer in the western half of the state.

After birth, a fawn will instinctively hide in the short-grass prairies of western South Dakota, camouflaged and out of sight from predators. But 140 feet in the sky, Helen Krueger, a graduate research assistant in ÈÕ±¾avÊÓƵ's Department of Natural Resource Management, observes the newborn deer through the lens of a thermal camera attached to a remote-controlled drone. After tracking the fawn's location, Krueger and her team of researchers use coordinates to find the deer's hiding spot. Once there, they blindfold the fawn and attach a GPS collar around its neck.

This work is part of a new project led by ÈÕ±¾avÊÓƵ assistant professor William Severud, an expert in wildlife ecology and a certified wildlife biologist. In collaboration with South Dakota Game, Fish and Parks, Severud and Krueger are conducting research to better understand South Dakota's mule and white-tailed deer populations.

"'Muleys’ and ‘whitetails’ are highly visible and important wildlife to South Dakota," Severud said. "Understanding how these populations change through time is a shared goal of South Dakota Game, Fish and Parks and ÈÕ±¾avÊÓƵ, and the university’s land-grant mission drives this work to provide science that informs management across the state."

In South Dakota, deer hunting is a popular outdoor activity in which over 60,000 residents participate annually. It also generates millions of dollars for South Dakota's economy each year. In 2023, the South Dakota Game, Fish and Parks conducted a survey of South Dakota landowners and hunters to better understand their perceptions and attitudes related to deer hunting. Many hunters felt that the white-tailed deer population in the state was "just about right," while also feeling that the mule deer population was "far too few." In response, the department has taken steps to increase the mule deer population in most of the western South Dakota counties while maintaining or slightly increasing the white-tailed deer population in many of the same counties.

White-tailed deer — which has an estimated population of 330,000 — are found in both the eastern and western halves of South Dakota. Mule deer — estimated at 110,000 — are predominately found in western South Dakota. Understanding population dynamics of both white-tailed and mule deer, and determining annual rates of population change, requires knowledge of juvenile and adult survival rates. Survival rates are used to estimate deer numbers and monitor changes in populations resulting from shifts in winter conditions, disease outbreaks or harvest strategies.

Severud, Krueger and the rest of the ÈÕ±¾avÊÓƵ team aimed to determine the juvenile survival rates for both white-tailed and mule deer in places where the populations overlapped. In South Dakota, many of the western counties have overlapping populations. For this year, the team's study focused on Haakon and Jackson.

Krueger traveled to the Philip area in late spring last year to conduct their first collaring season. By working with landowners and using thermal-camera equipped drones, the team — which included collaborators from the South Dakota Game, Fish and Parks — was able to collar 49 fawns, 23 of which were mule deer. The GPS-equipped collars allowed the research team to track the movements of the fawns as they aged.

"One of the most impactful tools in our research has been the use of a thermal drone for fawn searches," Krueger said. "This technology has greatly expanded the area we can cover with minimal disturbance to wildlife. The drone’s thermal capabilities have proven invaluable for locating fawns — on occasion we have located up to nine fawns in a single 20-minute flight."

The tracking did not last long, however. Survival rates were low for both species, with a survival probability to four months at 24% for fawns of both species.

"Mortality rates were highest during the first 50 days of life, after which survival probabilities leveled off," Krueger said. "No significant differences were detected across species or sex."

Krueger suspects that coyotes were the primary culprit for many of the fawns' deaths. The research team will determine the exact causes of death after sending DNA samples to a lab at the University of Washington.

"They will do DNA forensic testing," Krueger said.

While this year was rough for fawn survival, Krueger notes this doesn't mean that deer populations are in trouble. Survival rates can vary drastically from year to year, and the sample size is still relatively small. Still, the collected data does paint an interesting picture of the predator-prey dynamics happening in the western South Dakota landscape.

"The survival rate could be completely different next year," Krueger said. "Previous research on juvenile survival rates in other areas had high variations on a year-to-year basis. There's not a lot of definitive answers you can take away with just one year of data."

The research team was also interested in better understanding the hybridization rates of mule and white-tailed deer. Because the species are so similar and regularly interact and overlap, there is high probability mule/white-tailed deer hybrids exist in South Dakota. When the animals were collared, the research team took DNA clippings from their ears. These samples were brought back to the ÈÕ±¾avÊÓƵ campus, where they will be genetically sequenced by professor Jose Gonzales, the university's research core research support facilities director and founder of the Genomics Sequencing Facility.

This winter, Gonzales and his team will sequence the 65 samples the research team collected. Krueger expects a small percentage of the samples to show hybridization between the two species. This will be the first time hybridization among mule and white-tailed deer has been studied in South Dakota.

"With these results, we will hopefully be able to use hybrids as a group on its own to see how hybrids perform against peer individuals," Krueger said. "Are they surviving at the same rate? Do they venture further from their natural terrain? We will be able to look at these questions after understanding how many hybrids are potentially on the landscape."

Next summer, the research team will conduct the second part of the study in the historic Jasper Fire burn area of the southern Black Hills.

"Next year, we will have an increased number of available collars, with the goal to increase our sample size," Krueger said. "We will get a better understanding of the regional differences for the deer populations, as well as different predator interactions."