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DNR finds a new way to study fawns

by Parker Loew

Researchers have begun using thermal infrared drones over the last few years to study white-tailed deer fawns to help determine different causes of mortality.

This new technology is helping solve mysteries of how newborn fawns die in their first few months after being born and how they can potentially avoid predators.

Tyler Obermoller, a DNR natural resources specialist, walked through this cutting-edge project on Wednesday.

“We wanted to determine whether we could find a more effective way of locating newborn fawns in our study area, and that led us to drones with thermal infrared,” he said.

Obermoller is a deer biologist and the lead for the Fawn Survival and Movement Study in southern Minnesota.

His job is to study different aspects of deer ecology, such as survival, causes of mortality, habitat selection, and movement, and then help inform management objectives through hunting limits or habitat management.

“Ducks Unlimited took us out on the grassland area and launched a drone,” said Obermoller. “We quickly saw a doe with the thermal camera, and we immediately saw we had a lot of potential.”

In 2021, they fully implemented the thermal imaging drones into their research study and GPS-colored 75 fawns.

The following year they were able to collar 82 fawns, and in 2023 (this spring) they GPS-colored 104 fawns for survival movement monitoring.

Each year they have become more and more proficient at using the new technology to their advantage.

“We were able to take our drone out and evaluate and improve methodology,” he said.

Drones have become very popular over the last few years and have made researchers’ jobs much easier and more efficient.

They have made the research process less stressful on the animals as well.

Before drones, researchers would find and collar fawns by walking through the fields trying to get lucky.

This was rightfully and ironically called “optimistic capture.”

Another way they collared fawns was by vaginal implants in pregnant female deer, which would fall out when she gave birth, telling researchers the location of the fawn.

“For opportunistic captures and the implant transmitters, it takes a much larger crew and is less efficient,” he said.

One thing Obermoller is very careful about, regardless of method, is putting the fawns back exactly where they found them so the mother comes back to nurse.

While thermal imaging is great, it is not without its limitations.

“We found this technique was limited by sunlight,” Obermoller said.

When the sun comes out, the thermal heat signals they get from the ground start to blend together, and they are unable to tell where deer are.

Another limiting factor of the thermal imaging method with drones is not being able to tell different species apart such as adult deer, raccoons, fawns, coyotes and many other animals.

However, Obermoller said being able to tell species apart on the thermal imaging drones has improved as their methodology has improved.

Obermoller and his team were also able to resolve the sunlight issue by conducting flights at night or under cloudy conditions.

“We definitely found this capture method with the drones to be most effective and advantageous for our goals,” he said.

Obermoller uses these GPS collars to closely monitor survival and reduce their response time for mortality investigations.

This allows them to increase their ability to completely identify the cause of mortality in fawns.

Once they receive a mortality message from one of their GPS collars, they go to the signal to investigate.

“One of the first things we do when we find mortality is examine the site for different characteristics,” Obermoller said.

A few characteristics they look for are predator hair, tracks and scat.

If a mortality cause is unknown or appears to be health related and sufficient carcass remains, they will deliver the carcass to the University of Minnesota for an necropsy or an autopsy.

The GPS collars are programmed to send a mortality text message and email when the collar has been still for eight hours.

In 2021, they had 26 mortalities, with 17 coming from coyote kills, five from disease, and three from vehicle collisions.

In 2022, they had 47 mortalities, with 36 being from coyote kills, 4 from vehicle collisions, four from disease, and three from hunters.

Between 2021 and 2022, they saw a 91% increase in predation, mostly coming from coyotes, which is substantial and tells the researchers a lot about the changing dynamics of the ecosystem.

Over the next few years, Obermoller will be looking at how factors, such as habitat and bed selection, may help fawns evade better detection from coyotes.

Obermoller and many other deer and ungulate researchers have found the thermal imaging drone to be most effective for their goals of studying their given species.

The DNR plans to continue using this thermal imaging methodology to capture and collar ungulates for the foreseeable future or until other, better technology comes out.

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