If this winter’s 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, say wildlife officials with the Minnesota Department of Natural Resources.
“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, regional wildlife manager with the DNR at Grand Rapids. “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.
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 in Minnesota today because they have evolved to withstand severe winters. Despite the current decline in the deer population, wildlife managers are certain about a rebound in deer numbers, DNR officials said.
Following the two consecutive severe winters of the late 1990s, the deer population rebounded to pre-severe winter levels within two to three years and was at near record high levels within five to six 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.”
Fluctuations in deer populations are a normal aspect of wildlife management, DNR wildlife officials say, and with proper management and favorable conditions, populations can rebound quickly.