REGIONAL— A week of well-above-normal temperatures and an extended forecast showing generally mild conditions through the first week of March, is likely to be good news for the area’s deer population.
The area deer herd clearly benefitted from last winter, the mildest ever recorded in Minnesota. The mild conditions sharply reduced deer winter mortality and hunters in the region saw an effect as the hunter harvest jumped nine percent over the prior year this past November.
While deer numbers are still below goal due to back-to-back tough winters in the early 2020s, a second straight mild winter could bring an even bigger population rebound.
The stage for that was set in the first half of this winter, as the region experienced exceptionally warm and snowless conditions through early January. That left the deer herd in unusually good shape even as more typical winter weather arrived in mid-January. Now, six weeks later, an already below-average snowpack has taken a hit from temperatures near 40 degrees several days in a row. And with an extended forecast suggesting little new snow and continued mild temperatures through the first week of March, the prospects that the current winter will end on the mild side are improving daily.
The Department of Natural Resources uses it winter severity index, or WSI, to determine how winter conditions might affect the deer population. The index adds a point for each night below zero and for each day with at least 15 inches of snow on the ground.
As of Feb. 26, the WSI across all but tiny pockets of northeastern Minnesota was registering below 50. According to the DNR, any winter with a total severity index of 50 or less is considered mild, while winters with a reading of 51 to 119 are considered moderate, although there’s obviously a difference between a WSI of 60 versus 115.
And final WSI readings include the entire winter season, which means there’s a chance that this winter’s reading could still reach the moderate level. That would take considerably more snow and more below zero temperatures, which is certainly possible, but the prospects for a return to more winter-like conditions diminish in March.
As of Feb. 28, the average high in the region is 29.8 degrees with an average low of 1.4 degrees.
The DNR updated its WSI scale in 2020 to clearly define winter severity categories. Based on 36 years of data from winter conditions across deer permit areas in the northern forest zone, 25 percent of winters had values of 50 or less; 50 percent of winters had values of 51 to 119; and 25 percent of winters had values of 120 or higher.
Lower deer mortality may be expected during mild winters and higher mortality during severe winters. But the winter severity index is not predictive by itself, according to the DNR, because the simplicity of the point calculation does not account for the many other factors, such as habitat quality and the timing of spring green-up that can impact deer survival.
According to the DNR, white-tailed deer populations are very resilient due to their high reproductive potential. Annual pregnancy rates average 90 percent for yearlings and are near 100 percent for does from two-and-a-half to at least 15 years old, with more than half of those does having twins.
While winter severity and other factors can cause sharp decreases in deer populations, deer have the reproductive capacity to rebound quite rapidly and can do so if normal conditions continue for three to four years.