Bats in northern North America mate in the fall. The sperm stays alive in the female's body over winter. The young are born in the spring after developing for about six weeks. There is usually only one young bat born although twins are not uncommon. Bats hibernating in one roost seem to give birth all on the same day.
Young bats are unusual among mammals because they are born feet first.
The mother feeds her one or two youngsters on rich milk and often carries them on her back while she flies looking for food.