Scientists Regroup After Winterkill Wipes Out Mule Deer Herd Fawns

Aug 4, 2017

BLM wildlife biologist Mark Thonhoff fits a newborn fawn with a radio collar.
Credit Melodie Edwards

If you want to catch mule deer fawns, you’ve got to get up pretty early in the morning. It’s 5 a.m. when University of Wyoming Research Scientist Samantha Dwinnell gets on her computer. She checks signals emitted from a radio collared pregnant doe that shows she’s been hunkering down in one spot.

“Oh man, that’s beautiful,” Dwinnell says, laughing. “That’s exactly what we’re looking for,”

The doe’s been there all night and that means she probably gave birth. Dwinnell and her crew quick pack up their gear and jump in the truck to go find the doe, and hopefully her fawns. Deer almost always give birth to twins and they want to put radio collars on both of them. Last year at this time, most of the fawns from the Wyoming Range mule deer herd in western Wyoming were already born. But because of the severity of the 2017 winter, things are different this time. Dwinnell says ultrasounds show that fawns haven’t grown as big as they should have.

“So we had the harsh winter, we saw sort of a depressed fetal development. We weren’t quite sure what that means. So far what it appears to be meaning is that everything is delayed.

So they’re being born and they’re healthy, it’s just later?” I ask.

“Yeah, exactly,” says Dwinnell.

Some of the Wyoming Range mule deer herd migrates farther than any other in the world to get from their winter range up to their summer range in the mountains.
Credit BLM

Last year’s fawns, though, aren’t around anymore. Of the 67 fawn radio collared, all of them died. When their moms couldn’t dig down through the snow that piled up to 175 percent of normal, many succumbed to malnutrition. And life isn’t easy for this herd in the first place. Some of them make the world’s longest mule deer migration over rugged mountains, fighting off disease and navigating energy development along the way.

Wyoming Game and Fish Department’s Gary Fralick sits next to me in the back seat of the truck. He says this herd has been losing numbers for a while now and it was another bad winter in the early 90’s that started their slide. He says back then, Game and Fish tried to keep the herd size at around 38-thousand. But when it rose higher, the agency dished out more hunting licenses.

“During those two years of fairly liberal doe harvest was followed by an extremely severe winter in 1993. And those three factors—two years of substantial doe harvest and followed by a severe winter—really lowered the population,” says Fralick.

But even after the agency cut back on hunting, the population never rebounded. Now, there’s only around 20,000 in the herd. Fralick remembers some very angry hunters showing up at public meetings. Trucks wore bumper stickers that read, “Save a deer, kill a wildlife biologist.” It got ugly.

But Fralick says, back in ‘93, agencies didn’t have the hard science to back their policies. Now they have 24-years worth to help them answer some questions.

“What we need to understand is why these deer succumb so severely to some of these winters,” he says.

Research Scientist Samantha Dwinnell listens to signals from a mule deer doe's radio collar in hopes of tracking her down to find her fawns.
Credit Melodie Edwards

We follow the Greys River deep into the backcountry and start hiking. Dwinnell carries an antenna and receiver that beeps faster as we get closer to the doe. We do our best to tiptoe over the snow and fallen trees. Then we see the doe mosey by.

Dwinnell leans over and whispers, “We’re 40 meters from it right now. It’s good when they walk away slow like that. Often times they do that when they have a fawn, just try to be stealthy and quiet and sneak away.”

Mom is trying to keep us from finding her fawns. We start looking anyway.

But Dwinnell says moseying isn’t something this doe has done much of in the last couple months.

“She migrates from her winter range outside of LaBarge and Big Piney over the Wyoming Range,” she says. “All the deer in this population, or almost all of them, make these incredible journeys over some pretty gnarly terrain.”

Barbed wire fences, gas fields, subdivisions, this doe has seen it all. And after this winter, she’s lucky to be alive, according to Kevin Montieth, the University of Wyoming wildlife biologist heading this study.

“Of the adult females that were there at the beginning of winter, we’ve lost nearly 40 percent of them through the winter. Which is pretty striking to lose that many adult females,” Montieth says.

Normally, only about 15 percent die in winter. But Montieth says all this loss could be good news for survivors like this doe and her young.

“We now have many fewer mouth on the landscape to feed. It’s not necessarily what we want, but in terms of what that means for the individual animal that remains is potentially more, better food available to each one of them.”

Game and Fish’s Gary Fralick agrees there are benefits for science. He says it’s an opportunity to learn something about how mule deer pull through.

“This population will, in fact, recover as they have done for hundreds if not thousands of years,” Fralick says.

And because of the hard winter, the study has been funded for two more years.

It takes us a while but we eventually find the two fawns curled up under logs. Quickly, Dwinnell and Fralick begin weighing and measuring them as one of them cries in protest.

“I’m wanting to try to get blood on this one,” Dwinnell says, the syringe between her teeth, “but it’s kicking a bunch and I don’t know if I’ll be successful. You chill.” Then she says to me, “Just hang tight with her, if you don’t mind.”

So I do my best to hold down a squirming healthy fawn. The frustrated mom runs circles around us, huffing and stomping. The crew pulls radio collars over their tiny heads and takes photos “Yeah, I think we’re ready to go,” says Dwinnell.

“Ready to release them?” asks Fralick.

Then they let them go.

The fawns wobble off into the forest to hide again, camouflaged instantly. If they survive disease and predators, in a few months they’ll still have a looong walk into winter ahead of them.