The Southwest Wisconsin CWD, Deer and Predator Study is entering its second phase. Most of the fieldwork is finished, so now researchers are diving into the analysis portion of the project as data keeps rolling in.
This CWD study is the largest, most comprehensive deer research project ever performed in Wisconsin, and it is also one of the biggest CWD studies in the world. Dan Storm, Deer Research Scientist at the Wisconsin Department of Natural Resources (WDNR) and lead of the deer side of the project, said, “Its scale shows how seriously CWD is being taken.”
Storm continued, “CWD is here in a big way, and the problem is getting worse. Prevalence is increasing over time in the [counties] where it already exists and is spreading geographically. CWD is impacting a greater and greater portion of the deer population and portion of the people who interact with deer.”
Since its launch in 2016, the CWD Study has been focused on setting up the infrastructure needed for this project. The purpose of the capture component (Phase 1) of this project was to get the data generation machine flowing. GPS collars will continue to transmit their location until the animal dies or the collar’s battery runs out in 2-3 years, so the collaring phase was just the start of data generation, not the end. The animals need to keep living out their lives, and the GPS collars will continue to send us data about how they live and how they die.
Fortunately, the researchers have already received enough data from animals collared in past years to move into Phase 2 of the project. Phase 2 is where researchers begin to make sense of the stream of data they’ve been collecting. Storm said, “We’ve got a lot of good, quality data for this project. The more animals you catch, the more you can learn.” And if the 1,200+ animals that were captured and collared for this study are any indication, there is a lot researchers will learn about CWD in Phase 2.
What’s in store during Phase 2?
While data continues to flow in, Storm and his counterpart on the predator side of the study, Nathan Roberts, Furbearer Research Scientist at the WDNR, are ramping up the project’s data analysis phase. This phase aims to create a model for how CWD impacts our deer in Wisconsin. Roberts said, “We’ve realized that these [CWD] questions are really complicated. We can’t just look at a few variables at a time.”
Storm added, “These models are [therefore] very data hungry, because we have to account for so many different factors. Take survival, for instance. Right off the bat, you have differences in survival for each sex, age and CWD status. Just by having three different attributes to look at, you’ve already increased the sample size you need a bunch. Every little bit of complexity that’s added, increases the sample size needed.”
Roberts explained, “It is similar to how we think about human disease. You can look at the impacts of a disease on people, but that doesn’t tell you the whole story. To have a better understanding of what is going on, you need to look at some of the other factors like the impact of age or preexisting conditions. It’s the same with deer. You might think of predation even as a preexisting condition. We want to look at these important questions, not in isolation, but [together] with all these other factors that have the potential to impact the population.” Fortunately, Phase 1 was so successful at collaring a large sample size that the researchers will be able to look at CWD’s impact in a way that wouldn’t have been possible otherwise.
Why is modeling CWD so complicated?
CWD has the potential to change the likelihood that an infected deer dies from other causes, such as hunting, predation, and weather.
Let’s think of the deer population as a bag with ten marbles in it. Each year, three marbles are removed to represent annual deaths: one marble for hunting, one for predation and one for weather. At the same time, three marbles are added to represent that year’s new births, and the balance is maintained.
However, if CWD+ deer die more often during harsh winters, then two marbles need to be removed for weather (instead of one). Now, a total of four marbles are removed each year, yet only three are added. After a few years, there won’t be many marbles left in the bag.
Without incorporating these other variables and the potential of CWD to interact with them, researchers can’t fully understand the impact of CWD on deer.
Roberts said, “If we looked at these variables in isolation, it’s not very complicated. There [already] are models for individual factors like hunting or weather. What is unique here is that this study is comprehensive. We are integrating several sources of data into a single model.” With a large sample size and good analytical approach, such a comprehensive model is possible.
The researchers are currently at the beginning steps of building their model using the data that has already been collected, and more data will continue to flow in from the collars while the model is being built. Once the model is built and tested, the researchers will use the full dataset to analyze the effect CWD is having on the Wisconsin deer population.
David MacFarland, Wildlife Research Team Leader at the WDNR, said, “We are only at the halfway point. We still have a long road ahead of us.”
Upcoming Milestones in Phase 2
While we wait for the project to finish, we can look forward to a couple intermediate milestones. One upcoming milestone is the analysis of fawn survival. Since no new fawns are being collared, the monitoring period for these deer will finish soon, and the data can be analyzed.
Another milestone that our volunteers and nature lovers will enjoy is the analysis of juvenile dispersal. The year following their births, juveniles will begin dispersing around a larger area. In a few months, researchers will see the most recent batch of juveniles begin to disperse. Roberts said, “Each life stage presents different sets of challenges [for deer] and looking at each life stage gives us a fuller picture of the factors that influence deer populations throughout their lives.”
In addition to learning more about specific life stages of our deer, the researchers have also been expanding the team through collaborations. MacFarland mentioned bringing on research collaborators from the University of Wisconsin system and US Geological Survey during Phase 2. Two important collaborators, Alison Ketz, Assistant Scientist in the Department of Forestry and Wildlife Ecology at the University of Wisconsin-Madison, and Dan Walsh, Quantitative Ecologist at the U.S. Geological Survey’s National Wildlife Health Center, will play key roles in the model-building team.
Using our momentum
Phase 2 of the Southwest Wisconsin CWD, Deer and Predator Study is now underway and gaining initial momentum. The project’s success during Phase 1 set up the second phase to also be successful, and the researchers are confident that the project is in a great place. What we learn from this CWD study will better inform deer management decisions across the state, so stay tuned!
Roberts said, “In Wisconsin, wildlife are very important to our public. Wildlife and our communities are intertwined, so the public is very interested, not only in wildlife but having the information we need to make informed decisions regarding the management of wildlife.”
As a final thought, MacFarland said,
“If you care about deer, you should care about this project. CWD is a critical issue for deer management in the state. Like it or not, it is here and influencing our deer population.
If you are someone who values the ecosystems of the state, you should value this project. Deer are a primary influencer on our ecosystems. Not only on wildlife but on vegetation and other elements of the ecosystems. By understanding deer and their impacts, we learn about these critical ecosystems in the state.
If you care about conservation in Wisconsin, you should care about this project. The funding model we have for wildlife conservation across all of North America is based on funding through the sale of hunting licenses. Deer are the primary source of funding in Wisconsin. If there is something that is negatively impacting deer and therefore hurting deer hunting, then it’s negatively impacting the funding available for everything else we do in the state. The money that is generated not only funds deer management, but it funds prairie management, bird management, and the management of other important species.”
Stay tuned in this upcoming year for more from this study on the impact of CWD in Wisconsin.
What aspects of this project get the researchers excited?
MacFarland: “This project has been cool, because it is an example of what we can do as an agency and what we can do as a research group. The scale of this project is bordering on unprecedented, in terms of the number of animals collared and the scope of the project. This project is a testament to what is possible as an agency, especially when we have the cooperation of citizens.”
Storm: “For me, the biggest thing to learn [in Phase 2] is the main question: What really is the impact of CWD on the deer population? There are also so many other things [to learn] like how species interact with the landscape and how being infected influences how deer move across the landscape.”
Roberts: “I’m really excited to have a better understanding of the indirect impacts of carnivores on deer. We know that carnivores eat deer, nothing too surprising there. But with the work we are doing, we are able to look beyond that first level question of do they eat deer and ask what the potential indirect effects are. Does the type of habitat that they are using influence how deer move on the landscape? Being able to look at the indirect impacts of these species that all share the same landscape, that’s really fascinating, and I’m excited to see what we learn there.”
“That and… bobcats and coyotes are both secretive animals, because they are very cautious and elusive. They are common, but people don’t get to see them often. In this study, we have been able to look closely at those species in a way we haven’t been able to before. The number of animals and the technology we are using has really allowed us to look into the lives of these animals and the population as a whole. That’s been really fascinating to me.”
