Absent only from very remote oceanic islands, the high Arctic, and the Antarctic, bats are extremely widespread. For the most part, heterothermic species are the bats of temperate regions.

Some species of bats migrate hundreds of miles (kilometers) to avoid inclement seasons, but there is detailed knowledge in only a few cases. Schreiber's long-fingered bats (Miniopterus schreibersi) in Australia, noctules (Nyctalus noc-tula) in Europe, or Brazilian free-tailed bats (Tadarida brasiliensis) in parts of the New World are species whose seasonal movements have been documented by band recoveries. Seasonal appearances and disappearances of straw-colored fruit bats (Eidolon helvum) at different locations in Africa suggest migrations, and the same patterns have been used to support the proposal that red bats (Lasiurus borealis), hoary bats (Lasiurus cinereus), and silver-haired bats (Lasionycteris nocti-vagans) migrate in North America. In many other species, the seasonality of captures suggest migrations, but there are not documented movements of individuals (e.g., wrinkle-faced bats, Centurio senex).

The migrations of Brazilian free-tailed bats, like those of many insectivorous birds, allow individuals to remain active year-round because they follow their food supply (insects). Migrations of other bats (e.g., little brown bats [Myotis lu-

The spectral bat (Vampyrum spectrum) bares its teeth, which it uses to capture and eat small animals. (Photo by © Gary Braasch/Corbis. Reproduced by permission.)

cifugus], Indiana bat [Myotis sodalis], gray myotis [Myotis gris-escens], and Daubenton's bats [Myotis daubentonii]) are from summer habitats to hibernation sites. Underground sites (caves or abandoned mines) often are used for hibernation because they provide consistent above-freezing temperatures, often combined with high relative humidity. There are differences in hibernation site requirements (temperature, relative humidity) between species. In temperate areas, other species of bats (e.g., big brown bats, Eptesicus fuscus) use hibernation sites that are close to their summer roosts. Species like noctules hibernate in hollow trees.

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