The social behavior of an emerging breeding population of Eumetopias jubatus on the coast of Humboldt County

A population of Eumetopias jubatus and Zalophus californianus was studied during the summers of 1983 and 1984 on the coast of Humboldt County. The population of E. jubatus and Z. californianus peaked during June and August. Z. californianus numbers peaked again during September. The E. jubatus population probably formed an incipient breeding colony. During June a territorial bull showed sexual interest toward cows and attempted copulation. No pupping was observed. Sea lions moved to drier areas on the study site when tidal height and ocean surge inundated haul-out areas. E. jubatus and I. californianus formed segregated clusters when hauling out. Behavioral interactions between the two species were generally not aggressive. As colony size increased, rate of behavioral interactions decreased. Four age-sex classes of E. jubatus were examined. Old Bulls were highly aggressive toward other Old Bulls, used visual displays of aggression toward Sub-adult Bulls, and showed frequent sexual interest toward Cows. Sub-adult Bulls mock-fought frequently and were highly aggressive among themselves. They displayed a weak sexual interest toward Cows but were usually rebuffed. Cows and Juveniles were usually non-aggressive. Individual E. jubatus did not frequently respond to other sea lions. Such behavior may result from sea lion iii lethargy, or may be an adaptation whereby subordinates avoid antagonizing dominants. Moving E. jubatus also frequently avoided behavioral interactions.