Bats are so adapted to using these sound waves that they can detect a single strand of hair in total darkness. Most bats have their young in the late spring or early summer, after awakening from hibernation. Many bats will actually mate in the fall, hibernate through the winter, and then become pregnant in the early spring. This is called delayed implantation. Gestation is 30 to 60 days, and females usually have one or two pups per year.
Female bats nurse their young until the young are old enough to fly.
At this point, the pups follow their mothers, learning foraging techniques and strategies until they are able to hunt on their own. The female provides supplemental milk until the young are completely independent. The young ones must consume large numbers of insects each night in order to undertake migration and long hibernation through the winter months. Hibernation is an adaptation bats use to conserve stored energy at a time when their food source is unavailable or severely depleted. During hibernation, bats are very vulnerable to disturbance.