There are nine different species of bats that live in Vermont and New Hampshire. By far the most common is the little brown bat, which mates at about this time of year. The sperm remains in the female's reproductive tract until spring, when the eggs are fertilized. Mother bats help each other with rearing the babies, and, amazingly enough, each female recognizes her own offspring among the many of babies on the roost wall. As the mothers return from feeding, each baby recognizes its mother's voice, rears up, and calls to signal its location.
Final identification is aided by unique odors.
Wednesday Most bats raise just one youngster per year, and the mother is very attentive to its offspring. The first few days after the baby is born, the mother suckles it constantly, except when foraging for food. According to the National Audubon Society Guide to North American Animals , the young remain in the roost for about four weeks. They will begin to fly at 18 days of age, and after three weeks they have reached their full adult size. Male bats hunt for insects at night and roost alone in trees during the day.