Fawn study providing much-needed deer data in Minnesota’s farmland region

Madelia, Minn. — There are many areas of Minnesota where deer managers don’t have updated data in terms of fawn survival rates, but a study being conducted in the south-central area of the state is changing that in a portion of the farmland region. 

Wildlife researchers with the Minnesota DNR have completed two years of field work in a three-year fawn study that encompasses parts of deer permit areas 252, 253, 296, and 299. The work will paint a clearer picture of whitetails’ habitat use, provide dispersal information, and better pinpoint what kills fawns in this area of the state. The study will help managers get a better idea of how fawns are being recruited into the deer herd, providing information for population models that help determine regulations for hunters. 

“The main justification for this research is we needed an updated fawn-survival estimate for our population model,” said Eric Michel, an ungulate research scientist with the DNR. “There hasn’t been any fawn-survival work done in the farmland region since (about) 2002. We’ve had changes in the landscape, we’ve had (growth) in coyote populations.”

Collaring fawns and what data may reveal

Researchers collared more than 150 fawns in late May and early June in 2021 and 2022. The goal is to collar another 100 fawns this spring. 

The fawns are found by deploying a thermal-imaging drone over state wildlife management areas. Once deer are identified, researchers move in and quickly get to work on a handling process that takes around five minutes to complete.

Staffers take hoof and body measurements, draw blood samples, and place ear tags and GPS collars on the fawns. The status of the umbilical cord is noted (is it present and wet, dry, or not present at all?) and hoof measurements are used to help age the newborns. 

The average age of fawns captured in 2022 was estimated at 3.3 days old. The age was a little higher in 2021 – about 5 days. The mean estimated birth date for all fawns collared is May 25.

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Michel believes there is variance to peak breeding dates across the Midwest. An exact date is difficult to determine, but based on a gestation period of about 200 days for whitetails, this research would suggest peak breeding near Nov. 6.

“That’s going to be a bell curve with breeding taking place before and breeding that occurs after,” Michel added.

The GPS collars have folds in them that expand as the neck on the deer grows. The collars are advertised to fall off the animal at 18 months of age. 

Those fawns that live that long give researchers an idea of how far the deer are dispersing to establish home ranges, which can vary depending on where a study takes place. The farthest-dispersing deer in this study was a buck that went 67.7 miles before the collar stopped sending signals. 

The GPS collars send location signals every six hours, but they also record an activity data point every five minutes. That helps researchers understand fine-scale movements – how active deer are within their bedding cover, and how often they’re moving during daylight.

“All of that boils down to learning more about deer ecology and habitat use,” Michel said. “That could translate into habitat management.” 

Coyotes the biggest threat

Coyotes are the primary predators of fawns in this area of the state, the study has shown.

In 2021, 75 fawns were collared for the study. Twenty-six of them died, with 17 of those being killed by coyotes. There also were five health-related deaths, three vehicle collisions fawn fatalities, and one deer fell into a ravine and died. 

A total of 82 fawns were collared in 2022, and 44 died – 34 were killed by coyotes, four deaths were health related, three vehicle collisions killed deer, and three of them were hunter-harvested during the fall. Correcting for sample size, that was an 80.1% increase in coyote predation in 2022.

Other studies have shown that fawn survival can be highly variable. Tyler Obermoller, the lead on this south-central Minnesota research, didn’t wish to theorize as to what led to higher predation rates in 2022 until working through all the data.

“(The) biggest difference we are seeing is our sex ratios,” Obermoller said. “In 2022, we GPS-collared more male fawns, and they were significantly more vulnerable to predation. Specifically, we found 4.8 times more males predated than females.” 

Obermoller said he tends to focus on survival rates within the first three months of a fawn’s life.

“That is the most important (time period) for fawns,” he said. “If they survive the summer, their odds increase substantially to (survive) to one year.”  

The over-summer survival rate of fawns collared in 2021 was 78.1%. That dropped to 55.2% for the fawns collared in 2022.

“Within the population model realm, that variation is really important to capture because we can update that in the population model and incorporate that uncertainty and that variation around that estimate as well,” Michel said.

What makes fawns susceptible to predation?

When the study is complete, researchers hope to have some answers as to what might make fawns more susceptible to predation. They are taking multiple measurements at the bedsites of both surviving and predator-killed fawns related to cover.

“This will attempt to answer the question from the habitat perspective to determine whether we have good fawning habitat for predation avoidance and determine what bedsites fawns are surviving versus non-surviving,” Obermoller said.

Researchers are also examining the habitat types the mothers are selecting during the first months of life and comparing it to surviving and non-surviving fawns. 

“This is where we can try to bring in many different “map layers” such as Winter Severity Index, drought, temperature and try to make some associations,” Obermoller said.

The blood drawn from captured fawns is analyzed to examine different metrics that relate to stress and poor health. Researchers will also look closely at movement metrics of fawns to determine if certain fawns are more vulnerable to predation because they are not as active.

“We hypothesize more mobile fawns are better able to escape from predators via fleeing if and when they are encountered by a predator,” Obermoller said. “I treat this as another indirect indicator of poorer health, where fawns in poorer health may be less mobile and able to evade predators and therefore more susceptible to predation.”