Lions in the wild are usually sexually mature by 2 years old and most female lions (lionesses) have already reproduced by the age of 4. Lionesses go into heat several times a year and mate with one or more male lions dozens of times over the a period of a few days. Lionesses mate in order to ovulate. When a lioness is menstruating, the male lions of the pride (lion group) follow her until she chooses a mate. Some lionesses have more than one mate over the duration of the mating period. This may be done to increase the genetic diversity of her cubs and create a collective bonding among its members. The actual copulation lasts a few seconds but it is repeated a few times an hour and can continue for several days.
The gestation period lasts 15 weeks. When giving birth, the lioness retreats to a secluded den area, such as a marsh, cave or mountain hill. It is usually done from a standing position and the lioness uses her vaginal muscles to push the cub out of her womb. She gnaws the umbilical cord from the cub and cleans it of her fluids. Lions give birth to one to five cubs in each litter. Lionesses can give birth every two years.
Newborn cubs, weighing 2 to 4 pounds, are born blind, unable to walk well and their fur is spotted due to their leopard ancestors. After a few weeks, the cubs can see, walk and their spots fade away. They are defenseless and many die before they are 2 years old. Their mothers must protect them until they are able to defend against predators and hunt for themselves. She gives them her milk and brings them food. After six weeks, the mother leads her cubs to an animal that she has killed to give them their first taste of meat. They play together, which prepares them to hunt. The cubs begin hunting on their own after 11 months.
The lioness moves the cubs to a new den several times each month to avoid predators. She does not generally rejoin her pride until the cubs are 6 to 8 weeks old, allowing them to grow large enough to avoid being dominated at mealtime and starving. If another lion becomes pride leader, he will kill cubs that are not his offspring, so their mother must protect them. The cubs are weaned off their mother's milk after they are 6 to 7 months old. They usually leave or are forced out of the pride to fend for themselves and find their own prides. Their mother normally stays with her birth pride but some are forced to leave by a new pride leader. By 2 to 3 months old, the cubs weigh about 8 to 9 pounds and usually have all of their teeth. The mother then introduces the cubs to the pride for inspection.