Fort McCoy News Feb. 24, 2017

NRB staff monitors McCoy's deer herd through winter

Winter is often the toughest season on Fort McCoy's deer herd, so monitoring how the herd is dealing with winter conditions is crucial to the herd's survivability, said Wildlife Biologist David Beckmann with the Natural Resources Branch (NRB) of the Directorate of Public Works Environmental Division.

"Our over-winter deer population goal is to have 20 to 25 deer per square mile of winter habitat, which includes approximately 73 square miles of forested habitat at Fort McCoy," Beckmann said. "We use the winter population goal because winter conditions have the biggest impact on deer survival and reproduction. Populations over winter can deplete food and cover and impact forest regeneration and production, which could affect other wildlife species. Higher populations also can be more susceptible to disease if there is an outbreak."

Prior to 2006, Beckmann said the over-winter deer population on post ranged from the mid-30s to nearly 50 deer per square mile.

A whitetail deer is shown at a training area Feb. 6 on Fort McCoy’s North Post. The installation’s deer population is monitored regularly by the Directorate of Public Works Environmental Division Natural Resources Branch. It’s estimated that thousands of deer populate Fort McCoy’s 60,000 acres of land.
A whitetail deer is shown at a training area Feb. 6 on Fort McCoy's North
Post. The installation's deer population is monitored regularly by the
Directorate of Public Works Environmental Division Natural Resources
Branch. It's estimated that thousands of deer populate Fort McCoy's 60,000
acres of land.
Photo by Scott T. Sturkol

At these levels, deer can create a wide range of negative impacts on the landscape, such as reduced cover for military training concealment, increased collisions with vehicles, agricultural damage to adjacent farms, spread of ticks that carry lyme disease and anaplasmosis, soil erosion on hillsides due to heavy travel routes, and browsing of plants that are important for rare species, such as the Karner blue butterfly.

"The deer at that time were not as healthy, and there were increasing reports of winter die-off of deer," Beckmann said. "We started to reduce the population in the mid-1990s, and it took about 10 years of aggressive harvest to get to our current goal. And since we have gotten the population down to our goal, deer have been healthier, including having increased body weight, antler development, and fat content going into the winter.

"Healthier deer also resulted in increased fawn production with an increase of twins and triplets," he said. "This is a reflection of good nutrition before and during winter. As a reference, in the mid-1990s, we saw two years of extreme winters with freezing rain, snow, more freezing rain, and more snow. As a result, we had numerous reports of dead deer, especially fawns. But the stark impact was that pregnant does either reabsorbed or aborted their fetuses just to survive the winter. It was shortly after this that we saw the need to reduce the overall population."

Throughout each winter, NRB staff and contractors also go out in the field to see how the deer look and observe habitat fluctuations.

"Winter observation includes documenting areas with heavy deer use and areas that may be getting heavily browsed by deer," Beckmann said. "These are indications of areas where we may need to do habitat-improvement projects. They also document any dead or sick deer, again, to see what areas may need habitat work or if there are any indications of disease."

The health of the deer population after the winter also determines how many deer tags will be available for hunters later in the year, Beckmann said. That's why much work goes into making sure estimates on the overall population are accurate.

"We use a population model based on the (Wisconsin) Department of Natural Resources' Sex-Age-Kill model used until the early 2000s," Beckmann said. "Our calculations, however, included adjustments based on more than 30 years of harvest and population data at Fort McCoy. These adjustments are developed to provide a more property-specific model to evaluate population levels and trends."

In the mid-1990s, Beckmann said a researcher from Cornell University in Ithaca, N.Y., was looking for deer harvest and population data from various organizations to build the population structure of the specific lands.

"We provided him with 15 years of data, and he used that to reconstruct the Fort McCoy deer population," Beckmann said. "We did not provide him with our estimates at that time, but did discuss our evaluation of population trends. His results showed similar trends as we had seen, but our overall calculation of the deer population was higher in some instances. This is when we started to further look at factors that can be used adjust the population calculations to be more in line with our observations."

Adjustments made in calculating Fort McCoy deer-population estimates included incorporating variations in the birth of fawns (buck fawns vs. doe fawns), which can affect population growth.

"To provide another indication of the population trends, we also were able to maintain a life table based on the age of deer harvested and backtrack that to the year of birth." Beckmann said. "This ultimately showed us approximate births over 20 years, what percentage of the various age classes were being harvested, and what was available for reproduction.

"Our summer field crews and various volunteers also collect roadside survey data on deer from July to September," Beckmann said.

"These observations record the number of deer seen to include bucks, does, and fawns. Our main intent is to see how many fawns are reported per does seen. This gives us an indication of the birth rate, numbers of fawns produced per doe, and if there are any impact from the previous winter."

A healthy ecosystem is essential for a healthy deer population as well as for all wildlife at Fort McCoy, Beckmann said. That's why he said everyone on the NRB staff combines their skills in wildlife management, forestry, fisheries management, and natural-resources planning to keep the installation's ecosystem the best it can possibly be.

"Food and cover are key elements in winter survival for deer, as are places to get out of severe winter conditions," Beckmann said. "Healthy forests also contribute to a diverse ecosystem, providing adequate food sources (small mammals, fruit/seed, etc.) for some predators, such as coyote, wolves, and bear. This reduces the potential pressure these predators may have on young

Applications for annual deer harvest tags are typically available in late spring or early summer. More information about deer hunting at Fort McCoy can be found on the i-Sportsman website at For more information about deer management at Fort McCoy, call Beckmann at 608-388-5374.

   (Article prepared by the Fort McCoy Public Affairs Office and the Directorate of Public Works Environmental Division Natural Resources Branch.)