The Influence of Social Composition on Reproductive Behavior of Territorial Male California Sea Lions

The behavior of territorial males in a polygynous mating species may be influenced by a variety of factors related to site-specific conditions. In this paper, the behavioral dynamics of territorial male California sea lions (Zalophus californianus) are characterized throughout the breeding season and across rookery sites at Los Islotes Island in the Gulf of California, Mexico. Observations focused on three spatially distinct rookeries at Los Islotes that varied in the number and density of territorial males, the number of females, and the number of subadult males. Rates of male and female aggression were similar among sites and across the season. However, differences in female/territory defense and self-maintenance behaviors were exhibited by territorial males among sites and throughout the breeding season. Multiple regression analysis revealed a relationship between self-maintenance behavior and the number of females and males present. The time territorial males spent moving and in territorial maintenance was associated with the density of females within a territory. Males also exhibited higher levels of movement when more males were present. Finally, male California sea lions showed lower movement rates but higher amounts of time spent in territorial defense as the breeding season progressed. By comparing behaviors of territorial male California sea lions under different social compositions, this study illustrates the costs, benefits, and mechanisms of male territoriality.