PAUL A. SMITH, MILWAUKEE JOURNAL SENTINEL
If you care about Wisconsin deer—and if you’re human, I’d say you ought to—you’ll be interested in the latest update on state whitetail projects.
It was issued Dec. 10 and is titled “Wisconsin Deer Research Studies, Annual Report 2013-’14.”
The report summarizes the last two years of work to assess survival and causes of mortality in white-tailed deer.
I was particularly interested in the last years of data to see if the severe winter weather the last two years is reflected in higher deer mortality.
And the previous installments showed human hunting as the leading cause—by a wide margin—of mortality among adult and yearling deer.
Would that continue to be true?
And among fawns, would survival in northern Wisconsin continue to lag that recorded in the eastern part of the state?
We’ll get to the results shortly. First some background.
The projects began in 2010 and represent Wisconsin’s largest investment in deer research.
The work is a partnership of the Department of Natural Resources and University of Wisconsin. UW graduate students Andrew Norton and Camille Warbington have led the studies of adult deer and fawns, respectively.
Dan Storm, DNR ungulate research ecologist, is coordinating the work for the agency.
The projects are being paid for with $2 million from the Federal Aid in Wildlife Restoration Fund, an excise tax on firearms, ammunition and other hunting and archery supplies.
The research was launched at the request of the public. There has always been a curiosity about the leading causes of deer mortality.
Some in the public would argue that wolves are killing all the deer in Wisconsin. Others know that isn’t literally true but want research to inform their views on deer management.
A push for the research came, too, from those who wanted an improvement to the sex-age-kill model of estimating deer numbers. A factor called “buck recovery rate” is important to the accuracy of the model. Norton, the UW graduate student, also is using the work to study an alternate means of estimating deer numbers.
This study is providing Wisconsin data from two study areas: near Winter in Sawyer County to represent the northern forest and near Shiocton in Outagamie County to represent the eastern farmland.
The projects use radio collars to track deer. If a “mortality signal” is received, researchers travel to the site as quickly as possible in an effort to determine the cause of death.
Earlier this year, 133 adult and juvenile deer in the north and 122 in the east were trapped, fitted with GPS collars and released for the study. More than 50 other “carryovers” remain part of the study.
More than 1,000 volunteers participated in the projects over the last four years.
The fawn collaring and monitoring ended in 2013. Adults and yearlings will be monitored through early 2015.
So what do the latest results show?
In the big picture, human hunting trumps all other causes of adult and juvenile deer mortality in Wisconsin.
For the most recent full year (2013) of the study that includes hunting data, 67 percent of adult deer and 33 percent of juvenile deer mortality in the northern study areas was caused by hunters.
In the east, hunters were responsible for 70 percent of adult buck mortality and 50 percent of juvenile male deaths.
The data reinforce a long-held tenet: Hunting is key when considering harvest pressures on a deer population.
So, too, is habitat. In fact, the role of habitat in deer survival is woven through all the results, said DNR researcher Storm.
Biologists refer to it as “energetics,” or the amount of energy an animal can obtain from its environment.
“So much of deer survival comes down to how much fat they have,” Storm said. “It all starts with the condition of the doe coming through winter.”
Higher birth weights are linked to higher survival rates of fawns.
Further, if a doe is able to provide enough milk to its offspring, the fawn isn’t likely to “bleat” as much and might be less vulnerable to predators. A well-fed fawn also is more likely to be stronger and better able to elude predators, especially bears, earlier in life than fawns in poorer condition.
The 2013 fawn data showed 45 percent survival through six months in the north and 58 percent survival in the east. The leading cause of fawn mortality in the north was bobcat predation (25 percent), hunter harvest (19 percent), bear predation (12 percent), coyote predation (12 percent), unknown predator and wolf predation (12 percent), poaching and road kill (6 percent each).
In the east, starvation (47 percent) was the leading cause of fawn mortality, followed by disease (21 percent), coyote predation (10 percent) and domestic dog, hunter harvest, unrecovered harvest and bobcat (5 percent each).
The high rate of fawn starvation in the eastern farmland region—generally considered good deer habitat—leads to questions about the quality and availability of browse.
Habitat also is critical as shelter and cover for deer, including from the elements and from predators.
The winter of 2013-14 was the most severe on record for Wisconsin. How did the state’s deer fare?
From Jan. 1 to May 31 this year, 52 percent of juvenile deer died in the northern study area. That contrasts with the eastern study area, where 14 percent of juvenile deer died over the same time period.
While it is commonly said that adult bucks get so run down during the rut that they are more prone to succumb to winter weather, the study shows something else.
In fact, only one of 128 adult bucks monitored through May died of starvation. It was in the northern study area.
Here’s what the study showed about last winter: In the north, six of 67 adult and 34 of 102 juvenile males died between Jan. 6 (end of hunting season) and May 31, 2014.
The field work will wrap up in early 2015 and the researchers will begin compiling final reports. Although the DNR has contemplated doing similar studies in other parts of the state, no decision has been made, Storm said.
Although the final chapter hasn’t been written, I consider the projects a good investment in the management of our state’s single most valuable wildlife species.