Bats drink by skimming close to the surface of a body of water and gulping an occasional mouthful. Because insects are not available as food during winter, temperate-zone bats survive by either migrating to warmer regions where insects are available, or by hibernating. Several bat species hibernate in dense clusters on cave walls or ceilings. Clusters may consist of hundreds of bats per square foot. A few species reside in caves year-round, although they usually use different caves in summer than winter.
Most cave bats return year after year to the same caves.
Tree bats seldom enter caves. They roost in trees during summer days and spend winter primarily in hollow trees. Several species make long migration flights.