Wisconsin wildlife adapted to surviving cold, snowy winters
GREEN BAY– 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.
“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 category for severity. The last time we saw winters like these were in 1995-1996 and 1996-1997.
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.
Pritzl says the effects of winter stress are first apparent when a lower than average number of fawns survive.
“In any winter, regardless of its severity, the first animals to die are usually the sick, injured, old, or young that were born late the previous year. This is a natural process and is beneficial to a population in the long-term, resulting in stronger and healthier individuals within the population,” 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.
“The availability of high energy food is usually much greater; as a result, fewer animals will be food stressed,” Pritzl says.
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.
Wild turkeys recover rapidly after severe winters
Relative mild conditions in recent years, in addition to favorable habitat and agricultural practices, have also had a positive impact on the wild turkey population.
“Successive mild winters are certainly a contributing factor to the northward expansion of Wisconsin’s wild turkey population,” said Scott Hull DNR upland game specialist.
“Depending on the severity of the winter, turkey survival may be depressed,” Hull says. “However, wild turkeys have proven themselves to be extremely resourceful animals by feeding on a variety of foods and restricting their movements during harsher weather to conserve energy.”
Hull says wild turkeys can remain in an inactive state during periods of inclement winter weather for up to two weeks without food, and can recover from a 30 percent weight loss.
“Starvation and predation are usually the ultimate causes of death during extended periods of deep snow and cold temperatures. But these losses are usually minimal, and wild turkey populations recover rapidly following severe winters.”
In fact, Hull notes, following the severe winter of 1995-1996, spring turkey hunters set a record high harvest at the time.
Winter feeding does more harm than good
Despite the apparent severity of the 2007-2008 winter, wildlife biologists strongly advise against feeding deer and turkeys.
Feeding deer is illegal in roughly the southern third of Wisconsin and those who feed songbirds and squirrels in these areas must make sure that feeders are inaccessible to deer.
Feeding wildlife, biologists say, can actually do more harm than good for various reasons, including enabling weak and sick animals to survive, increasing dependence on unnatural food sources, and increasing the potential for the spread of diseases.
Deer and turkeys survive the winter by finding areas with a combination of good thermal cover and natural sources of balanced nutrition.
“Wisconsin wildlife are physically and behaviorally adapted to survive winter weather,” said Pritzl.
“If artificial feeding occurs, these animals may be drawn to sites because it is an easy food source, but most of the time these sites are not near their preferred winter cover,” he said.
Supplemental feeding also often causes animals to change their natural movement patterns, which can increase the odds of animal/vehicle collisions, and increase their vulnerability to predators. It may also concentrate animals in areas where they will also feed on ornamental trees and shrubs in residential areas.
“Biologically, artificial feeding is not the best approach to helping any wild animal during severe winters,” Pritzl says. “Maintaining populations that can be supported by natural habitat is the best course of action.”
FOR MORE INFORMATION CONTACT: Jeff Pritzl, Green Bay - 920-662-5127
