Determinants of outcomes of agonistic interactions among male California sea lions (Zalophus californianus)

Agonistic behavior in territorial male California sea lions (Zalophus californianus) may be influenced by multiple factors, including who initiates an interaction and who owns the territory on which an encounter takes place. We studied predictors of the outcomes of agonistic interactions between territorial male California sea lions on 3 islands (Los Islotes, Granito, and San Jorge) in the Gulf of California, Mexico, during the 2005 breeding season. We evaluated both displays and fights among males to examine the hypotheses that initiators of agonistic interactions and that territory owners were more likely to win disputes. The outcomes of agonistic encounters (win or lose) were independent of the types of interaction (displays or fights) by the initiator and, hence, all agonistic interactions were pooled for analyses. We used an overdispersed binomial logistic regression to determine if initiators and resident males were more likely to win an interaction than noninitiators and nonresidents, respectively. We found that initiators of agonistic interactions were more likely to win agonistic disputes. Resident and nonresident males were equally likely to initiate agonistic interactions and were also equally likely to win agonistic disputes. Our results suggest that agonistic interactions among male California sea lions are influenced by which individual initiates the encounter and not by territory ownership.