For many small mammals, habitat is a simple consideration. Individual mice or shrews may not travel 100 meters in a lifetime. Their habitat choice is narrow and can be described simply: grassland, moist meadow, ponderosa pine woodland. For bats, however, description of habitat is a very complex proposition. For one thing, the habitat is three-dimensional. There are daily movements from roosting habitat to foraging habitat through intervening "commuting habitat." There may be a seasonal migration across a variety of habitat types to hibernate.
The habitat of mammals often is described by the characteristic vegetation. This makes good sense for many species but not necessarily for bats. First, temperate zone bats are insectivores, and as such, they are at least one "link" in the food chain removed from direct dependence on plants (the "producer" level of the ecosystem) for energy. Second, only a few of our bats depend directly on vegetation for cover. Two species of Lasiurus both roost in trees, as does the silver-haired bat, but most other species select roosts by physical features Ñ rock overhangs, crevices, caves, mines or other human-made structures. Rocky cliffs clothed with woodland or shrubs or grasses may look very different to a packrat, a rock mouse or a human being, but these different habitats are fundamentally the same to a crevice-roosting bat.
Note that a number of species use buildings, bridges, mines and other structures. Bats' strong reliance on such human-made habitats may be more apparent than real, of course. These are, after all, easy places to observe bats, and they are more often frequented by human observers than non-cultural habitats. It is easy to observe a long-eared myotis or a fringed myotis in an outhouse or along the ridge pole of a barn, but one is unlikely to encounter them in a tree hole or behind the bark of a rotting snag, their natural habitat. Despite that consideration, humans have increased habitat for some species. In Colorado, for example, mining has increased habitat for such cave-dwelling species as Townsend's big-eared bats because natural caves are scarce in the Southern Rockies.
Water is an essential feature of habitat for most bats. Nearly all species come to water (a pond, still pool or quiet eddy in a stream) to drink.