Soon after giving birth mothers enter oestrus and mates again with the male in territory. The mother then leaves her pup behind to find food in the sea. Since Otaria byronia mate and breed synchronously with hundreds of other sea lions, pups are better protected from predators and abduction when the mother is away. This promotes group bonding among pups. However, this group lifestyle also triggers the mother's aggression level toward other female sea lions in defense for her pup.
Mothers return from their feeding trips in intervals to nurse their young.
They are able to locate their pup by first calling to them and then identifying them by smell. Sometimes mothers are separated from their pup and are not successful in finding them. This can be due to several factors such as high tide, storms, male abductions, and inexperienced young mothers. Larger populations experience higher pup mortality because of the greater risk of pups being trampled to death by adult sea lions. Pups spend most of their time in groups or pods playing, sleeping, or residing near the water.