The female lioness forms the stable social unit of their group called a pride. They typically do most of the hunting for their group as they are more effective hunters, and are smaller, swifter and more agile than males. Lioness do not tolerate outside females into their group. Membership into the group changes only with the births and deaths of lionesses. Although, some females do leave and become nomadic. Most lionesses will have reproduced by the time they are four years of age. Their average gestation period is around 110 days. Females give birth to a litter of one to four cubs in a secluded den or other area away from the rest of the pride. Usually, the mother does not integrate herself and her cubs back into the pride until the cubs are six to eight weeks old.