As the cold deepens and the snow falls in Chicago, the beloved and gentle deer who inhabit the surrounding suburbs and wooded areas enjoy traditional offerings of apples, pears and other foods brought to them by their many admirers.
As for the northernmost herds inhabiting the shoreline region of Lake Superior, where the low temperatures are severe and the snowfall heavy and of long duration, they must migrate in search of conifer cover for protection from the snow and wind.
Unlike deciduous tree types, conifers offer thermal protection and are capable of intercepting large amounts of snow. According to a Michigan Department of Natural Resources and Environment report, between 60-90% of deer around the shores of Lake Superior must migrate from 10 to 50 miles to find suitable conifer forest habitats.
Conifer habitats must provide both food and shelter and contain adjacent browsing areas consisting of forest types that will provide winter food for deer such as woody plants, shrubs, tree seedlings and saplings, herbaceous plants, agricultural crops, treetops from timbering and blowdowns and supplemental feeds.
While deer in areas of moderate snow depth of short duration do not stray far from their summer ranges, but rather seek conifer cover within those ranges, the northernmost deer must migrate or risk becoming trapped in over 4 feet of snow. The high levels of snowfall in the upper peninsula region is an aspect of 'lake effect snow' that occurs as cold arctic air moves over the warmer waters of the Great Lakes. In some areas the snowfall can continue for days . At Keweenan Peninsula, which juts out into Lake Superior, the winter snow accumulation totals between 200-300 inches.
The Michigan Department of Natural Resources and Environment compiles a Winter Severity Index that reflects the estimated effect of winter weather conditions on the energy reserves of deer and its potential impact on the herd. Current approaches of the Wildlife Division seek to provide a common basis for mapping and managing deer populations by providing a common understanding of winter habitat components of deer, defining and refining terminology through a review of the scientific literature and by developing methods with which to map winter habitats of deer in more nuanced ways that include variability in the existing and potential landscape conditions.