After arrival on shore, males fast for three months, and females fast for five weeks during mating and when nursing their pups. The gestation period is about 11 months. Sometimes, a female can become very aggressive after giving birth and will defend her pup from other females. Such aggression is more common in crowded beaches. While most females nurse their own pups and reject nursings from alien pups, some do accept alien pups with their own. An orphaned pup may try to find another female to suckle and some are adopted, at least on Año Nuevo Island. Pups nurse about four weeks and are weaned abruptly before being abandoned by their mother, who heads out to sea within a few days. Left alone, weaned pups will gather into groups and stay on shore for 12 more weeks. The pups learn how to swim in the surf and eventually swim farther to forage. Thus, their first long journey at sea begins.