The colonization of Southeast Farallon Island, California, by northern elephant seals, Mirounga angustirostris, began in 1959 with the appearance of a single animal. By 1971, over 100 juveniles were counted during the fall and spring haulout. Breeding began on the island in 1972. The age of juveniles and their pattern of island use for the two years preceding the birth was similar to that of Año Nuevo Island, a nearby rookery. The majority of seals onshore during the fall and spring peaks were juveniles less than two years old. Tagged individuals sighted on Southeast Farallon Island were born on rookeries to the south: Año Nuevo Island, San Miguel Island, and San Nicolas Island. Males were observed more frequently than females. Utilization of the hauling-out place by juveniles was not determined primarily by availability of space. During the first breeding season, adult females arrived on the island before the first male was observed.
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Ainley et al. (1974) studied this question.