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Whitetail Catch And Release: Studying Deer In The CWD Hot Zone

Wildlife ecologist Nancy Mathews admits she had a few anxious moments last November. As part of a chronic wasting disease study, Mathews had dozens of deer traps set in two areas of the CWD “hot zone” in south-central Wisconsin, she had a team of technicians standing by to tag the deer and attach radio collars, and she had a veterinarian on call to sedate the deer and take tissue samples … but she had no deer.

The traps, baited with a mouthwatering mix of corn and molasses, received very few visitors until mid-January, when serious snow and cold weather hit. “I was a little embarrassed when the deer didn”t come in to the traps in November,” Mathews says, “but I knew they would when they were sufficiently stressed by the weather. Since the winter weather arrived, we”ve had tremendous trapping success.”

Using traps, drop nets and rocket nets, the team trapped and released about 60 deer by late March. Some were repeat visitors returning for the free lunch, but as of April 1, 36 free-ranging deer were wearing radio collars (and Mathews expects to collar a lot more). The collared deer are monitored and located several times a week. Their movements over the coming months and years will fill some blanks in our knowledge of deer behavior, and may provide keys to controlling the spread of CWD through Wisconsin”s deer herd.

This project has four goals, according to Mathews.

o Determine the dispersal rate of yearling deer. The movements of these deer are likely to spread CWD across the landscape.
o Monitor movement of adult bucks. During the fall breeding season, rutting bucks may wander 10 miles a day seeking estrous females, making them likely candidates in spreading the disease. So far, the researchers have collared six buck fawns and five adult bucks.
o Identify social groups of adult does, because they probably serve as reservoirs for CWD. Radio telemetry will help the researchers to understand the rate of interaction within and among the social groups.
o Document where and when deer spend time with cattle on the landscape. There”s no evidence that CWD can infect cattle, but given the high numbers of deer on many farmlands, livestock producers are understandably nervous.

Mathews now has about 40 traps at two sites near Mazomanie and Arena. All the traps are on private land. “Some of the landowners support the DNR”s position and some don”t, but they all back our research,” Mathews says. “We”ve been pleasantly surprised by all the support we”ve received from the landowners.”

The landowners haven”t always gotten good news about the deer on their land.

A veterinarian performs a tonsil biopsy on each trapped deer before it”s released. So far, the biopsies have shown two adult does positive for CWD; those animals have been killed. Tissue samples from the infected deer were sent to the UW Veterinary Diagnostics Laboratory in Madison and to Dr. Judd Aiken”s lab at the UW School of Veterinary Medicine; further testing may reveal whether fetuses can get infected before birth.

Mathews expects to see more positive deer during the study; hunting data collected by the Wisconsin Department of Natural Resources show that 10 percent to 20 percent of the deer herd is infected in the trapping areas. She plans to run the traps as long as deer keep coming to the bait, and collar as many deer as possible.

If she can find funding, Mathews hopes to add two more trapping sites outside the intensive harvest and management zones. Data from these sites, near La Crosse and Boscobel, should help researchers determine if the deer are moving differently in areas with lower hunting pressure.

Deer in Mathews” current study areas were hunted all last summer and fall, as well as all winter, and they”ve changed their daily routine, becoming less active at twilight and shunning fields during the day. “We don”t see the deer in the fields, but we”ve had good success at night with traps placed inside the woods,” Mathews notes. “Using infrared cameras at the baitpiles, we”ve verified that the deer are more active at night.”

Radio telemetry may have documented a migration, which is not good news for wildlife managers hoping to slow the spread of CWD. A collared doe and her fawn moved 5 miles from their original home range and stayed there, setting up a new home range.

“This is highly unusual for southern Wisconsin – we don”t usually see large seasonal migrations this far south,” Mathews says. “This may have implications for the spread of CWD, since we”ve developed all the models and computer simulations without considering seasonal movements. Seasonal migrations will make things worse if infected deer move across the landscape.

“This is absolutely not a result of hunting pressure,” Mathews adds. She pointed out that a team of sharpshooters followed an infected doe who led them in a big circle for a whole day before eluding them. Two days later they found her again back in the center of her home range. Telemetry showed that she never left the boundaries of her home range while she was being followed.

This project is scheduled to run at least 5 years, and Mathews says it is likely to run for much longer as deer begin to re-populate the landscape.

A graduate student, a field coordinator, and six technicians are all working full-time on this project. “Between morning trapping and night-time rocket netting, crew members have been working 15- to 18-hour days,” Mathews says. “They have to monitor a 72-square mile area, which is a lot of landscape to cover, and they”ve done it every day — in sub-zero temperatures, snow, rain and mud. The dedication of these young biologists has been essential to the success of the project to date.”

Salaries, the costs of safety training and clothing, and a long list of expensive hardware, including radio collars, clover traps (metal-framed net traps) and Stephenson box traps, add up to a lot of money, and Mathews is extremely grateful to the project”s supporters. This research is funded by Whitetails Unlimited, the National Cattlemen”s Beef Association, and the Wisconsin DNR.

“Whitetails Unlimited has been a tremendous resource for us. They were the first to contribute resources to our project, and they acted quickly and without hesitation,” Mathews says. Tim Van Deelen, deer research coordinator at the DNR, is cooperating on this research. “The DNR has participated and encouraged the research, because they”re well aware that they don”t have all the answers,” she says. “They”ve gone to extraordinary lengths to facilitate this work. The National Cattlemen”s Beef Association has funded nearly half of the research project costs and has shown interest in a longer term commitment to the work. Without these major contributions, this research would not have been possible.”