California sea lions do not have a stable social organization during the nonbreeding season (August through April).
California sea lions are extremely gregarious and form large aggregations when on land. Individuals lie close to each other, or even on top of each other.
Large male California sea lions exhibit size-related dominance over smaller animals.
When in the water, California sea lions often form small groups.
During the breeding season, California sea lions gather in rookeries for pupping and breeding.
On land, sea lions aggregate in protected areas near shore.
In the water, they may form a raft: a small mass of sea lions on the surface in very close proximity.
Juvenile and nonbreeding California sea lions are perhaps the most playful of the otariids. They often ride the surf, chase each other, push and shove each other off rocks, and practice territorial battles. Adults engage in these activities less often.
In response to sudden or unusual activity (such as a loud noise or rapid movement), one or a few individuals start toward the water. This begins a rush as the rest of the herd follows. This alarm reaction is less pronounced during the breeding season.
Dominance behaviors are most aggressive during the breeding season. Males establish dominance by open-mouth threats and vocalizations, pushing, and shoving.
Territorial behavior in males is strongly correlated to mating behavior. At the onset of the breeding season, male California sea lions establish breeding territories.
Dominant male California sea lions maintain territories from May through August, but territorial behavior is most intense between late June and early July. Galápagos sea lions maintain territories until January.
A male's territory extends beyond the water's edge and is partly aquatic. Various physiographic features (i.e. boulders, tide pools, reefs) serve as borders.
Boundaries are poorly defined and vary according to time of day, temperature, and movement of the females. Average size of a territory is about 130 square meters (1,400 square ft.). Males are frequently observed along the beach at 10-15 m (33-49 ft.) intervals.
Males establish territories by incessant barking, chest-to-chest pushing, grappling, and biting. Fights may result in injury, but are rarely fatal.
Once territories are established, males patrol their boundaries and bark when necessary to maintain and defend them. An intruding male evokes and immediate response from the resident male, who struggles violently to displace the intruder. To reaffirm their borders males often engage in ritualized boundary displays. One such display is when two bordering males rush at each other, barking. When they reach the border they stop barking, fall on their chests, and, with mouths open, shake their heads from side to side. They then rear up and stare obliquely at each other. Bull also patrol the aquatic borders of their territories by swimming along the territories' edges.
Territories exist only when and where females are present. Females, however, are relatively indifferent to the territories and move about freely between them. Males make no attempts to herd females or prevent their departure.
California sea lions often rest and sleep on land and in the water.
A sea lion may raise a flipper out of the water to regulate its body temperature.
Sea lions often "porpoise"; that is, they leap out of the water while swimming and re-enter headfirst.
Interaction With Other Species
California sea lions share haul-out space with northern elephant seals, harbor seals, northern fur seals, and Steller sea lions. California sea lions frequently interact with these species in much the same way as they interact among themselves.
California sea lions normally coexist peacefully with other marine mammal species, but breeding males, and females with newborn pups, may threaten and chase intruders. During breeding season, territorial disputes between male California sea lions and fur seals usually result in a victory for the more aggressive fur seal.
Pups and juveniles may snap at and briefly chase gulls.