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 (email@example.com) or phone (989.356.3596 x102).
For many forest landowners in northern Michigan, wildlife habitat management ranks as a primary ownership goal. While white-tailed deer, black bear, ruffed grouse, American woodcock, and other game species are usually of primary interest, the majority of vertebrate wildlife species in our forests are non-game species. In fact, most of our forest wildlife are secretive, cryptic, and/or migratory, spending only the breeding season in northern Michigan. To introduce the reader to some of these species and how specific forest structures provide wildlife habitat, below I will describe a hypothetical forest wildlife community inhabiting a hypothetical 40-acre forest property during late Spring. Our imaginary forested property has 30 acres of northern hardwoods and 10 acres of lowland conifers. The property has both mature trees (40 feet tall or more and 40-100 years old) and immature trees (seedlings and saplings less than 20 feet tall). The northern hardwood forest is comprised of big-tooth aspen, red maple, and sugar maple, with a few scattered large eastern white pine and red oak trees. It once had eastern hemlock and white spruce, but these species were removed decades ago and are no longer represented. White ash was also part of this forest, but non-native, invasive emerald ash borer killed all the trees. The lowland conifers include black spruce, balsam fir, tamarack, and northern whitecedar. The first wildlife species encountered on our property is the gray treefrog. Because our property has “vernal ponds” (seasonally wet spots that dry out come summer in the northern hardwoods) and some standing water in the lowland conifers, a number of different species of amphibians exist on the property. Our gray treefrog is one of the more cryptic. We hear it, but don’t see it. The color of its skin blends in perfectly as it sits on a limb of a red maple on the edge of the northern hardwood patch. Only the trained ear can discern the odd song of this species from other sounds in our forest. The male’s odd song will attract a female that will lay eggs in our vernal ponds and other standing water. The next wildlife species we encounter on our property is a strikingly colored, and consistently vocal, male American redstart. This small, migratory songbird is one of the more common forest bird species in the eastern United States and males are dramatically colored with orange, black, and white. Our male is defending a breeding territory in a 1-acre patch in our northern hardwood forest, spending most of its time in young maple saplings less than 1 inch in diameter. Its mate, yellow-brown and secretive, is sitting on three eggs in a small nest in a sapling sugar maple only 6 feet off the ground. When the young hatch, they will be fed protein-rich insects collected by both parents. Because of the water and the cover in the adjacent lowland conifers, there are lots of insects in our forest and the young grow quickly. Come August, they all will migrate to the Caribbean. Our final two wildlife species are using one tree, just different parts of it. A large big-tooth aspen has formed a perfect crown into which a great-horned owl pair nested the previous February. Now, the two chicks are nearly full grown and are out of the nest, looking for small mammals as prey. Because this aspen is over 100 years old, decay has started to cause some of the limbs to break off and fall to the forest floor. Here, the fallen limbs provide cover for an array of plant, fungi, and animal species, including the pygmy shrew that hides from the owl. This shrew is a member of the second smallest species of mammal in the world, and is most active at night. Because of its high metabolism it eats continuously and is now searching for insects and other invertebrates that are using the fallen limb as well. All told, our 40-ac property provides conditions for many more wildlife species than space allows us to mention here. While game management can provide habitat for some non-game species, forest wildlife diversity is usually a result of complexity provided by “composition” (the mix of tree species) and “structure” (the vertical and horizontal arrangement of live and dead trees) specific to a given forest site. Composition and structure for the present and the future can be a focus of forest planning and management. And if identified as a landownership goal, forest planning that takes into account natural models of how forests form and function can provide a blueprint for maintaining forest wildlife diversity. 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 (firstname.lastname@example.org) or phone (989.356.3596 x102).
Dr. Greg Corace
Want to hear about what is new in the science world? Maybe get more information on the birds around us? Or maybe you want to keep up to date on what is happening in our current environment and with the natural resources we love. Check out some interesting articles shared by our Forester, Dr. Greg Corace.