In winter, they either hibernate or fly thousands of miles south to warmer places. Only a few species migrate south. Hibernating bats have a problem. If the place where they hibernate falls below freezing, they die. If the cave or building is too warm, they will use up their store of fat too quickly and starve to death.
Bats can wake up from hibernation very quickly.
They can escape danger that way. Other animals that hibernate take much longer to wake up. Solitary bats who live alone, except to mate, roost among the leaves of trees. Social bats cluster in groups in sheltered places such as caves, hollow trees, and under roofs.