Large groups may be frightened into the water by the appearance of a person. Yearlong, circadian activity pattern. Adult males maintain terrestrial and aquatic territories in breeding season. Breed May to August. Highly polygynous, adult males establish and defend territories.
Preferred territories contain highest number of females, and controlled by largest breeding bulls.
Males maintain territories for 2-6 wk. Females give birth to a pup 1-2 days after arrival, come into estrus and mate about 2 wk following parturition. Mothers begin to leave the pup at 4 days of age, making progressively longer feeding trips at sea. Accumulation of nitrogen compounds from large rookeries enriches nearby waters. Late spring and summer prey of California sea lions, Zalophus californianus, near San Miquel I. California, 1978-1979.