South American Sea Lion - Social Behavior and Reproduction

Social Behavior and Reproduction

Mating occurs between August and December, and the pups are born between December and February. Males arrive first to establish and defend territories, but then switch to defending females when they arrive. A male will aggressively herd females in its territory and defend both from neighbors and intruders. On rocky beaches, males etablish territories were females go to cool off and keep them until estrous. On cobble or sandy beaches, males have territories near the surf and monopolize females trying to get access to the sea. The number of actual fights between males depends on the number of females in heat. The earlier a male arrives at the site the longer his tenure will be and the more copulations he will achieve. Males are usually able to keep around three females in their harem, but some have as many as 18.

During the breeding season, males that fail to secure territories and harems, most often sub-adults, will cause group raids in an attempt to change the status-quo and gain access to the females. Group raids are more common on sandy beaches than rocky ones. These raids cause chaos in the breeding harems, often splitting mothers from their young. The resident males will try to fight off the raiders and keep all the females in their territorial boundaries. Raiders are often unsuccessful in securing a female, however some are able to capture some females or even stay in the breeding area with one or more females. Sometimes an invading male will abduct pups, possibly as an attempt to control the females. They also take pups as substitutes for mature females. Sub-adults will herd their captured pups and prevent them from escaping, much like what adult males do to females. A pup may be mounted by its abductor but intromission does not occur. While abducting pups does not give males immediate reproductive benefits, these males may gain experience in controlling females. Pups are sometimes severely injured or killed during abductions.

Sea lion mothers remain with their newborn pups for nearly a week before making routine of taking three day foraging trips and coming back to nurse the pups. They will act aggressively to other females who come close to their pups, as well as alien pups who try to get milk from them. Pups first enter the water at about four weeks and are weaned at about 12 months. This is normally when the mother gives birth to a new pup. Pups gradually spent more time in the nearshore surf and develop swimming skills.

South American sea lions are observed to make various vocalizations and calls which differ between sexes and ages. Adult males will make high-pitched calls during aggressive interactions, barks when establishing territories, growls when interacting with females, and exhalations which are made after agonistic encounters. Females who have pups make what is called a mother primary call when interacting with their pups, and grunts during aggressive encounters with other females. Pups make what are called pup primary calls. Some of those vocalizations and acoustic features may support individuality.