REGIONAL—Deep snow since relatively early this winter season has been restricting deer movement for weeks, but the mild temperatures have kept the winter severity index, or WSI, from hitting …
REGIONAL—Deep snow since relatively early this winter season has been restricting deer movement for weeks, but the mild temperatures have kept the winter severity index, or WSI, from hitting the severe range, at least for now.
The WSI is a gauge of winter severity for whitetail deer. It includes a point for every 24-hour period with a below zero temperature reading and another for every day with at least 15 inches of snow on the ground.
As of Wednesday, WSI readings around the region ranged from around 50 near Lake Vermilion to as high as 80 closer to the North Shore, where deep snow has been in place longer. Typically, cold weather is responsible for most of the WSI points in northern St. Louis County, but this winter has been dominated by abundant snow and mild temperatures.
And that could give a false impression of the WSI reading this winter compared to most recent years. According to DNR Tower Area Wildlife Manager Tom Rusch, the depth of snow and the duration of deep snow are the most significant factors affecting whitetail deer survival in northeastern Minnesota, since it impacts their ability to access food and escape from predators. By contrast, “very cold and dry winters have little impact on deer,” according to Rusch.
Recent winters with abundant snowfall, and varying temperatures, have combined to limit the recovery of whitetail deer in recent years, and it appears this winter could end up as yet another in that series. Rusch notes several permit areas in the region remain below goal for deer density, and have yet to recover from heavy snow winters in 2013 and 2014.
Rusch, who recently spent considerable time in the air for the DNR’s annual aerial moose survey, said he was struck by the lower numbers of deer spotted during the recent survey. “We’re seeing fewer deer on the landscape,” he said.
An ongoing study of whitetail deer near Elephant Lake, north of Orr, has found close to 40-percent mortality for deer in that region. That kind of mortality, which Rusch said has been fueled both by abundant snow in recent winters and limited winter cover in the Elephant Lake area, has prevented the deer herd in that area from showing signs of recovery.
Rusch notes that quality deer habitat requires both adequate browse— which is more available in young, recently disturbed forests— and sufficient mature woods, particularly with conifers, to provide deer with thermal protection.
How deer fare this winter will still depend on the weather that the area experiences over the next two and a half months. Barring an early melt, the area appears likely to exceed a WSI reading of 120, which is considered a moderate winter in northern St. Louis County. But given the lack of cold temperatures so far, it would appear unlikely that this winter will reach the “severe” category, which includes winters that exceed a WSI of 180 points.