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Winter effect on deer herd gauged

January 21, 2011
The Mining Journal

Winter has fully settled in after a rather mild December, with January slipping by like the blink of an eye. Inhabitants of the region have pretty well settled into their normal winter routine, as well, with ice anglers out on the ice, rabbit hunters hitting the swamps, skiers, snowmobilers and snowshoers cruising woods trails and couch potatoes staying close to the fireplace and TV as the NFL playoffs get more exciting each week.

The various wildlife species of the Upper Peninsula have settled into their winter routines, too, which can vary greatly depending on the species.

Those that hibernate are slumbering away peacefully in their dens while those that stay active through the winter are mainly focused on finding enough food to survive.

Article Photos

Whitetail deer in the northern Upper Peninsula have a difficult time surviving the winter, especially if snow and cold weather arrive early and lingers into spring. (Dave Schneider photo)

Perhaps the most at-risk creature of the woods is also one that many human residents of the region have a special interest in - whitetail deer.

Deer up in our neck of the woods mostly head to deer yards for the winter, where they find food and protection from the elements in the thick conifer woods.

To gauge the impact of the winter on deer, the Michigan Department of Natural Resources and Environment uses its Winter Severity Index. The index is used to measure the impact of the winter on whitetail deer, as well as other wildlife species. Started in the late 1960s, the index is calculated by tracking wind chill, snow depth and snow compaction from November through April.

In the old days, veteran wildlife biologists like Lou Verme and John Ozoga, who worked for many years at the state's Cusino Research Station, helped develop the index by gathering data weekly from a chillmeter and a snow compaction gauge.

The system was revised in 2005 to use data available from the National Weather Service, a method that reduced the man-hours needed to collect the information and resulted in more consistent measurements.

While not a tool to determine how many deer actually die during the winter, the index is useful in determining the potential impact of the winter on the deer herd in various regions of the state.

Coupling this data with other monitoring results, such as spring dead deer counts in deer yards, can help biologists manage the deer herd better.

Last winter, for example, there were some usual ups and downs early through mid-winter, and then the index showed a major downward deviation from the average for the last six weeks or so of the winter.

Seeing that early and late are the two critical times of the winter for whitetails, having an early end to winter indicates more younger deer made it through winter and pregnant does were healthier than normal, resulting in more and healthier fawns being born.

That certainly seemed to be the case as many hunters reported seeing a lot more younger deer in 2010 than during the 2009 hunting seasons, which came on the heels of two harsher winters in a row. Those harsh winters did result in a reduced U.P. deer herd, which was reflected in the early estimate of the 2010 deer kill being about the same as in 2009 - a year that was down nearly 20 percent from the year before.

Thus far, the winter of 2010-11 has been about normal with a few exceptions. It started a little slow but quickly shifted into high gear by mid-November, with the index well above the average by the beginning of December.

Then, as often happens in the U.P., the weather took a big turn and was milder than normal in mid-December, sending the WSI below the average.

It has risen quickly over the past few weeks and is running about normal for mid-winter, which is usually when the index is at its highest point.

Deer can handle rough weather during the middle portion of winter, though, as their metabolism slows and they lay low and use fat supplies to survive.

But then March rolls around and things start picking up for deer and their fat supplies are nearing depletion, so the herd needs winter to break early to head toward summer in good shape.

It would certainly be nice to see another winter that doesn't take a big toll on a herd that's already smaller than a lot of people would like to see. To keep an eye on the index, log onto the website at and click on the Winter Severity Index tab.

Editor's note: City Editor Dave Schneider can be contacted at 906-228-2500, ext. 270. His e-mail address is



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