Usually, they mate in autumn before hibernation starts. Over the winter, females store the males' sperm, a feature unique among mammals. Fertilization of the egg usually occurs in early spring. Young are born at the end of spring and the beginning of summer. Tropical bats often reproduce twice a year, following seasonal patterns in food availability.
Bats give birth usually to one young.
There are only very few exceptions where bats regularly give birth to two or more young. At first, the young bats cannot fly because their wings are not fully developed. For two to six weeks, the female takes care of the baby, keeping it warm, grooming it, and feeding it milk. During that time, a strong bonds exist between mother and young. Mothers recognize their own young even when they have to identify them within huge aggregations of hundreds or even thousands of other baby bats.