The Role of Aggressive Behavior in Male Territorial Disputes
Jacobs, David F.; Hernandez, Claudia M.C.; Young, Julie K.; and Gerber, Leah R.
School of Life Sciences, Arizona State University
Male sea lions, like other polygynous mammals, exhibit agonistic behavior during the mating seasons to obtain territories and improve their fitness. Our goal was to study the role of aggression between adult males and to examine how aggression relates to male residency. Because aggressive interactions can be costly, we hypothesized that male California sea lions may have intrinsic mechanisms for determining the outcome of aggressive interactions before engaging in such interactions. Two hypotheses to explain this idea include the Ainitiator always wins@ hypothesis, where the initiator of an interaction has a greater chance of winning the interaction and the Aresident always wins@ hypothesis, where the resident of an interaction has a greater chance of winning the interaction. To test these hypotheses, we recorded male agonistic interactions at breeding sites on three islands in the Gulf of California, Mexico (Los Islotes, Granito, and San Jorge Islands) during the 2004 breeding season. We recorded the time, date, and island where the interaction took place, the identity of the two males involved, and the length of all agonistic interactions. The interactions were separated into two categories: aggression and fight. The outcome (win or loose) was independent of the type of interaction for initiators (χ22 = 0.66, n = 106, p < 0.05). Initiators were more likely to win aggressive disputes than receptors (χ21 = 8.3, n = 27, p < 0.05 & χ21 = 12.2, n = 79, p < 0.05), but the initiator was independent of residency (χ23 = 3.73, n = 66, p < 0.05). These results suggest that male California sea lions may posses a mechanism to determine the probable outcome before engaging in aggressive interactions.