Fertilization does not occur until the end of hibernation, and gestation takes about 60 days. Parturition occurs in late May to early July. Female Indiana bats typically give birth to one pup. Juveniles are weaned after 25 to 37 days and are able to fly around the same time. Most young can fly by early to late July, but sometimes do not fly until early August. Humphrey and others reported an 8% mortality rate by the time young were weaned. However, they assumed that all females mate in the autumn, which is not the case, so not all the females would give birth. Thus, mortality of young may be even lower than 8%.