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Southwest Wisconsin CWD, Deer & Predator Study Newsletter

Issue 7: November, 2018

In this issue of Field Notes we cover the process behind collaring carnivores and fawns, and further discuss what we can learn from the data we collect afterward. We also hear about one hunter’s experience harvesting a collared deer. Finally, we’re excited to introduce you to the crew leaders heading up carnivore and adult deer collaring this fall and winter.

Click the titles below to read this issue’s full articles and view our videos.

crew with collared fawn
Numbers Update: 2018 Fawn Collaring and Summer Survival
We’re sharing the raw numbers from summer fawning season.

majestic bobcat
Collared Carnivores
CWD is a deer disease, so why study carnivores?

youth with harvested collared doe
Fair Game: Hunting Collared Deer
You're up in your tree stand, weapon at the ready and a collared deer appears in your sights. Can you shoot this deer, or is it off-limits?

new deer crew leaders
Meet the Crew
Carnivore trapping is underway, and deer trapping is about to start. Meet some of our returning crew veterans.

Numbers Update: 2018 Fawn Collaring and Summer Survival

Crew holding a collared fawn

For the second summer in a row, the CWD crew set out to radio collar 100 fawns and subsequently tracked their movements. The purpose of this is to determine how many fawns survive into fall, which gives us a good indication of fawn recruitment, or the number of fawns that go on to become part of the breeding population. As we discussed in a previous article, recruitment is an important factor in calculating herd growth, which in turn helps us understand how many CWD mortality events the herd can withstand before the disease begins to affect overall herd size.

Last year, we nearly reached our goal with 91 fawns. This year, we exceeded it. With the help of more than 300 amazing volunteers, we collared 104 fawns.

Newborn fawns spend their days tucked into dense cover while their mothers roam in search of food. Their excellent camouflage not only keeps them hidden from would-be predators, but from our researchers as well. Fawns in southern Wisconsin are born once spring green up is well underway. At this point the hayfields are high and the understory in the woods has filled in. To find as many fawns as possible, our crew and hundreds of volunteers carefully comb the woods and fields in our study area.

“I’m pretty impressed that we did it. Our crew was ready to go, and our volunteers really stepped up,” said Daniel Storm, deer and elk research scientist with the Wisconsin DNR, “but the heat wave over Memorial Day weekend set us back right at the peak of fawning season.” To avoid the heat, our crew waited for nightfall and continued their search by spotlight.

“We couldn’t have reached 104 fawns without our volunteers,” said Storm. This coming spring, we’ll be looking for more volunteers to join the search. “Collaring 100 fawns is a lofty goal, but with a large number of volunteers, we can do it,” Storm said.

We collared our first fawn on May 7. May 22 was our best day with 13 fawns collared, and we wrapped up with our last fawn on June 21. Like last year, we caught an even split of 52 bucks and 52 does. The heaviest was a male weighing in at 17.9 pounds, and the smallest was a 4.4-pound female. The marked difference in size was likely due to the male fawn being several days older than the female.

Of course, collaring is only the first step to learning about fawn survival within our study areas . Beginning when we collared our first fawn on May 7 and ending August 31, crew members drove the back roads of our study areas with a radio antenna, scanning the air waves for signs of fawns. Provided the fawn moves at least once every six hours, its collar will beep every second. If the fawn hasn’t moved for more than six hours, the collar will start to beep once every half second.

When we hear those half-second beeps, our crew will use radio telemetry to pinpoint the collar’s location and investigate the scene for a possible mortality event. Over the course of the summer, up to 38 of our 104 fawns died. (Death is not always certain in these cases because it can be unclear whether the fawn has died or simply lost its collar. In a previous article, we looked into how our crew handles this uncertainty in their mortality investigations.)

This summer, there were six cases in which we found only the collar. Without remains or other signs of mortality, we can’t say for certain what happened to the fawn. If we assume these six unsolved cases were mortalities, then 38 of the collared fawns died. If we assume none of them died, then our mortality count comes to 32 out of 104. The truth is probably somewhere in the middle. As we gather more data throughout the study, our analysis will account for these unknown cases.

For the fawns with a known cause of death, predation by coyotes was the most common cause. This appeared to be the case for 24 of our fawns. Bobcats were considered the most likely culprit for three more. It can be difficult to tell the difference between coyote and bobcat predation, so the actual numbers could be a little higher on the bobcat side and lower on the coyote side. Once again, our models will account for this uncertainty as we gather more data.

While predation was the lead cause of mortality among the collared fawns, we believe the ample forage and dense cover of southwestern Wisconsin help the fawns stay hardy and hidden, mitigating the risk of becoming a meal.

Fawns can also die from disease and exposure. One fawn died of a severe bacterial infection, another from a wound of unknown origin and yet another from either disease or starvation. In other cases, the cause was man-made. A collared fawn died from a collision with a motor vehicle, and one was caught in haying equipment.

Even with these mortality events, 66 of our collared fawns survived, each of whom presumably went on to join southwest Wisconsin’s breeding population of white-tailed deer. Each summer we spend collaring fawns and monitoring their survival broadens the scope of our knowledge and allows us to further analyze how our deer population fares in a landscape with disease and predation.

Collared Carnivores

A bobcat in winter

Chronic Wasting Disease (CWD) is a deer disease, so why do we also study carnivores?

To better understand the effects of CWD on white-tailed deer in southwestern Wisconsin, we must consider all the major factors that drive deer population dynamics. While predation does have an impact on an individual deer, how it impacts the overall population remains unclear, and its effects in a CWD-endemic area are even murkier.

Within the study area for our project, deer primarily have two wild predators: coyotes and bobcats. Both species are found throughout the study area and both can kill or scavenge white-tailed deer. We are collaring coyotes and bobcats with GPS units to collect information that will improve our understanding of the local carnivore community and how these species may impact deer in a CWD-endemic area.

To properly examine this predator-prey relationship, it is important to understand the predators themselves. We are using GPS data to determine population densities for coyotes and bobcats as well as what drives population dynamics for both species. Understanding these two variables will help us gauge the influence that carnivores may have on deer populations in our study area.

Over the past three years, we’ve trapped and collared 45 coyotes and 28 bobcats within 10 miles of our study area boundary. Our wildlife technicians capture animals through their own trapping efforts, and we rely on 25 local trappers and landowners to help us find them. As with deer, we investigate every time there is a mortality event to better understand what drives population growth or decline. We’ve also developed an algorithm to determine when an animal has established a den or a prey site. We call these locations cluster sites because they center around a cluster of GPS points. When a clustering event is identified, we investigate the site to determine if it represents a predation or birth event. In doing so, we are able to gain information on the predation rate for deer as well as reproductive information on carnivore species, both important components in our models. Over the past two years, we’ve investigated a total of 234 cluster sites as well as 139 random GPS locations.

Collared animals allow us to document movement, showing us the habitat use, home range size and density of these species. The collars also let us see how long they live, which in turn allows us to estimate the size of carnivore populations and to determine whether they are growing, shrinking or remaining stable. Finally, we can identify how frequently a collared animal consumes a deer. All of these pieces of information further clarify the complex relationship between white-tailed deer, CWD and carnivores.

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Fair Game: Hunting Collared Deer

Collared deer are legal to harvest with standard license and tag.

You are poised in your tree stand for the third hour in a row, weapon at the ready. The sun crawls into the sky, the morning fog dissipates and finally, after what seems like an eternity, a deer wanders into your sights. However, there is something different about this one. It’s wearing a clunky collar. Can you still shoot this deer, or is it off-limits?

Collared deer, who have been equipped with GPS units as part of the DNR’s Southwest Wisconsin CWD, Deer and Predator study, are completely legal to harvest and should be treated like any other deer. A collar or ear tags do not denote the status of the deer’s health, nor do they indicate whether it has been infected with Chronic Wasting Disease (CWD). The Southwest Wisconsin CWD, Deer and Predator study is a research project designed to improve our understanding of how CWD impacts Wisconsin’s deer population. These collars allow us to map a deer’s journey across the landscape and to determine the cause of its eventual mortality, by CWD, hunter, car or otherwise.

If you were going to shoot the deer, you should. All that is required of you then is to dial the number on the collar. A DNR official will come directly to you and retrieve it. You’ll also get a host of information on the deer you harvested.

17-year-old Josh Richardson was hunting on the Iowa County property of a Deer Management Assistance Program (DMAP) cooperator when he spotted a collared deer.

“After I saw the collar, at least to me, it looked like the most mature deer in the field. I talked to the landowner [and] he told me to treat it like any other deer,” said Josh.

He described the DNR researcher who responded to his subsequent call as “very helpful”. “They came right to where we were, a very quick response, I don’t think we were waiting for more than ten minutes,” he said.

In exchange for his time, Josh received maps that recorded his deer’s movements over the course of its life, as well as an estimate on the deer’s age.

“I was sent the maps, the collar locations, and I thought it was pretty cool to see just how close that one doe stayed, she never really left more than a half by half mile radius,” said Josh.

If you call the number on the collar and there is no answer, we ask that you please leave a message containing the following information: the collar frequency or ear tag number, the date of harvest and your contact information, including the area code.

Whether the deer you harvest has a collar or not, we encourage you to have the deer tested for CWD. Visit and search keyword “CWD sampling”, or call (888) 936-7463 to learn more.

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Meet the Crew

Fall carnivore collaring is already underway, and we’re gearing up for adult deer capture this winter. Our crew leaders are all project veterans this year, and they’re excited to be back to set trap lines and more frozen drop nets. Hey, it’s not for everybody, but we love it out here!

Last revised: Thursday May 16 2019