Winter Wildlife Habitat

The first wildlife management text in the United States was Aldo Leopold’s Game Management (1933). Leopold saw that game populations responded positively to habitat management. He also proposed that species-specific wildlife habitat consists of food, water, and cover. Nearly 100 years later, we know that wildlife populations are impacted by many other things. Nonetheless, food, water, cover, and space (as a newly added fourth variable) still structure how we think about wildlife habitat for individual species. How does space come into play in wildlife habitat? For some wildlife species, including many Neotropical migrant songbirds, space is used differently during the breeding season, during migration, and on the wintering grounds. Throughout migration routes, space provides birds the ability to restore energy reserves by resting and foraging for food. Birds that struggle to find suitable space during migration from their wintering grounds to their breeding grounds may arrive in poorer physical shape, potentially reducing their ability to reproduce successfully. Space is also critical for wildlife species with exceptionally large home ranges or “area-sensitive species”. Area-sensitive species not only require a certain condition of vegetation structure (vegetation arrangement) and composition (mix of plant species), they also require large blocks of habitat (space). In northern Michigan, the upland sandpiper and sharp-tailed grouse are bird species of fire-dependent, pine and oak barrens, as well as pasture and hayfield complexes. Both species require hundreds or thousands of acres of unfragmented open habitat. Similarly, black-throated blue warblers are only found in large tracts of mature, mixed forests of northern Michigan. A forest must be many hundreds of acres or more to be occupied by this migratory bird species. Of the four variables of wildlife habitat, space is perhaps the most challenging to provide in a world increasingly dominated by human land uses. Not surprisingly, many species requiring large spaces are of conservation concern. [Authors note: the importance of “landscape context” previously covered applies here.] How can a landowner provide wildlife habitat, especially when space is limited? Let’s think specifically about our winter wildlife. While wildlife diversity in northern Michigan is reduced during the winter months due to migratory birds wintering elsewhere, it is also during the winter when some species move into our area. Snowy owls, pine grosbeaks, red crossbills, common redpolls, pine siskins, and American tree sparrows are encountered more often during our winter as birds from farther north move south. For many of these and other species, cover and food are very important during the winter. Fortunately, cover and food can be provided in a number of ways, regardless of whether a property is in the city or in the country. For example, landowners can provide cover by having patches of their land devoted to native coniferous trees. When a property has coniferous trees of different ages, sizes, or species, a “layering” of vertical structure results. In the winter, these areas provide some refuge from the wind and precipitation, while still retaining heat. One of the reasons white-tailed deer seek swamps of northern white-cedar, black spruce, and tamarack is the “thermal cover” and reduced snow depth these areas provide. Private landowners can also provide cover by retaining large live or dead trees with flaking bark or cavities. Wildlife such as southern flying squirrels and white-breasted nuthatches find refuge from harsh winter conditions in these spaces. And dead material, like a pile of decomposing leaves and branches on the forest floor or in the corner of a backyard, can provide many small mammals, such as meadow voles and deer mice, with cover. Some reptiles and amphibians may use these warm, quiet places to hibernate. Mature coniferous trees, such as red pine and eastern white pine, also provide energy-rich seeds. Red crossbills evolved with beaks that are offset from one another. These beaks allow the birds to pry open pine cones. Birds then extract seeds with their strong tongues. Some deciduous trees also provide winter food. Young aspen is browsed readily by white-tailed deer, elk, and snowshoe hare; ruffed grouse eat the buds of more mature trees. While not a favorite for those interested in timber products, ironwood is favored by many birds in the winter because it retains seeds throughout the year. Like all professional fields grounded in science, our knowledge of forest and wildlife ecology is dynamic. As our forests change due to succession, management activities, or other reasons out of our immediate control, wildlife use can also change. By studying and understanding how the natural world operates, forest managers can devise wildlife habitat management activities best suited for a forest and the suite of native wildlife species adapted to its conditions. Greg Corace is the forester for the Alpena-Montmorency Conservation District. For more information, including sources used in this article, Greg can be contacted via email (greg.corace@macd.org) or phone (989.356.3596 x102).