Mild winter should help boost deer population
While winter weather may be far from over, this winter has been mild by Minnesota standards. If mild conditions persist, those conditions combined with a conservative 2014 deer harvest could signal the start of a rebound in the state’s white-tailed deer populations.
“Now past the half-way mark in a typical winter season, most areas of Minnesota are accumulating relatively few points on the winter severity index (WSI) map,” said Jeff Lightfoot, northeast regional wildlife manager with the Minnesota Department of Natural Resources. “Last year at this time, indices in much of northern Minnesota were already building toward a severe winter.”
The winter severity index is a general measure of winter conditions based on prolonged cold temperatures and deep snow that can restrict deer movement and access to food. The current WSI in most of northern Minnesota was 79 or less as of Monday, March 2.
An area can accumulate points each day throughout the winter season. One point is assigned when the daily temperature reaches zero degrees or lower, and another point is assigned when snow depth is 15 inches or more. Each day can accumulate 0, 1 or 2 points.
End-of-season values less than 100 indicate a mild winter. End-of-season values more than 180 indicate a severe winter. In general, northern Minnesota wildlife managers start seeing significant increased fawn mortality around 130 to 150; does around 180. Of the two factors, deep snow is the greater challenge for deer because of the energy expended to navigate in it and its decreasing effect on food availability as snow continues to cover food sources.
Deer exist today because they evolved to withstand severe winters. Despite the current decline in the deer population, wildlife managers are certain about a rebound in deer numbers.
Following the two consecutive severe winters of the late 1990s, the deer population rebounded to pre-severe winter levels within 2 to 3 years, and was at near record high levels within 5 to 6 years.
A landmark 15-year study (1991-2005) by the DNR followed 450 collared does through mild, average and very severe winters. The study yielded a wealth of data on the food habits, migration patterns, survival and cause-specific mortality rates, and reproductive ability of deer in Minnesota’s forested zone.
“Deer have an incredibly high reproductive potential with mature females 2-1/2 to 15-1/2 years old nearing a 100 percent pregnancy rate each fall,” said DNR wildlife research scientist Glenn DelGiudice. “If mild conditions persist, we could expect to see good fawn production with healthy birth weights, along with does that are in good condition to meet the physical demands of nursing.”
Fewer deer on the landscape means less competition for available food. Late winter to early spring is an important time for deer. Like most mammals, a deer fetus gains most of its weight in the months just prior to birth, so does that are able to maintain some fat reserves through the winter have the best chance for bearing healthy fawns.
Fluctuations in deer populations are a normal aspect of wildlife management and with management and favorable conditions, populations can rebound quite quickly.
Winter severity maps are updated on Thursday each week and are posted on the DNR website at http://files.dnr.state.mn.us/recreation/hunting/deer/wsi_cty_map15.pdf.