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Despite record breaking snowfalls in southern Wisconsin and cold temperatures statewide, hunters and residents should not be alarmed about this winter’s impacts on wildlife, according to state wildlife officials.

Department of Natural Resources offices have been receiving many inquires about how deer, wild turkey, and other species are surviving the winter. This winter has actually been closer to normal for Wisconsin, they note, compared to the exceptionally mild winters in recent years, and deer and turkey populations have evolved to withstand these varying conditions.

“Winter mortality is a natural process and can be important in keeping wildlife populations in balance with their habitat,” said Jeff Pritzl, wildlife supervisor for the DNR Northeast Region at Green Bay.

Each winter, the DNR monitors the Winter Severity Index (WSI) in northern Wisconsin. The WSI was developed in the early 1970s to provide an index of winter impacts to deer populations. It is calculated by adding the number of days with 18 inches or more of snow on the ground to the number of days when minimum temperatures were zero degrees Fahrenheit or below between Dec. 1 and April 30. March will be a very telling month for judging the effects of this winter. Continued winter conditions through March could have an impact on deer recruitment, say state wildlife officials.

“If you think of it as adding up points, a day when both conditions occurred would get two points,” Pritzl says.

At the end of April, all the points are added up, resulting in the WSI number for the whole winter. A winter with an index of less than 50 is considered mild, 50 to 80 is moderate, over 80 is severe, and over 100 is very severe. Very severe winters in northern Wisconsin can result in up to a 30 percent direct loss in the deer population.

Wildlife biologists say it is still too early to make any conclusions about this year’s winter. Many sites in northern Wisconsin are currently in the “moderate” to “severe” category for severity.

The last time Wisconsin experienced "very severe" winters were in 1995-1996 and 1996-1997. Biologists think this winter will likely end up being more similar to the winter of 2000-2001 when the average WSI in the northern forests ended up at 83 (severe).

DNR wildlife staff use the WSI to develop antlerless quotas for the upcoming deer hunting season. The DNR’s deer population model is built to assume a winter of moderate severity. When WSI values indicate a severe winter, the number of available antlerless permits in regular units for the upcoming deer season may be reduced.

The effects of winter stress are first apparent when a lower than average number of fawns survive, according to Keith Warnke, DNR big game specialist.

"If you think of winter’s impact on deer as a continuum of increasing severity, the first affects will be doe fawns not giving birth to new fawns in the spring, then fawns from the previous year will die, then bucks will die, then adult does will not give birth to fawns, and last, adult does will die," he says.

“Some people think we’re having a hard winter in northern Wisconsin, but our perceptions are colored by the fact that the Northern Forest region has experienced 15 mild winters during the most recent 20 years,” said Keith McCaffery, retired DNR deer biologist.

Wood County Wildlife Biologist Wayne Hall reported snow depth and temperature values in central Wisconsin that reached a moderate WSI through the end of February. And Wildlife Biologist Michele Windsor in the Black River Falls area reports significant snow depths this winter – greater than 18 inches. Windsor noted that foresters were seeing higher deer concentration this winter in cut-over areas that were adjacent to thick stands of pine.

The WSI is seldom applied to the farmland regions of the state. In these areas, biologists say, winter impacts on deer and turkey survival are generally minimal.

Biologists say the availability of high energy food is usually much greater; as a result, fewer animals will be food stressed.

In most winters, WSI values would normally be much less throughout the farmland region compared to the northern forests. For instance, Jake Fries, DNR wildlife biologist for Dane County reported that WSI values in the Madison area are in the mild category through the end of February.

In southeast Wisconsin, some deer have been reported yarding up this winter, which is unusual for that part of the state.

“This has been especially notable in the Kettle Moraine State Forest and the Sheboygan Marsh,” said, Tami Ryan, DNR Southeast Region wildlife supervisor.

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terry ford wrote on Sep 7, 2008 2:24 PM:

" I would like to have baiting banned in Wisconsin. Sitting over a bait pile is not hunting. Looking for deer signs, scouting, and finding an oak ridge is the definition of deer hunting. When the winters get rough, the deer who are dependent on piles of corn suffer the most because after deer season the baiting stops. Wisconsin should allow corn piles after the hunting season and not during the hunting season. "

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