Agonistic behavior, which includes aggressive behavior and responses to aggression, is one of four general categories into which the behavior of humans and all other animals can be divided. The ubiquity of agonistic behavior makes it broadly relevant not only to basic science but also to practical problems from the population to the individual level. One kind of site-specific agonistic behavior, territoriality, is particularly amenable to study because its spatial localization allows measurement of its costs and benefits under field conditions. However, it is often difficult to evaluate both costs and benefits in a common unit that is strongly correlated with survival and reproduction. Dr. Ewald will carry out field experiments with one of the few study subjects for which these obstacles can be readily surmounted: hummingbirds defending feeding territories. For this subject, both costs and benefits can be quantified in units of energy and experimentally manipulated; moreover, the rapid responses of hummingbird territoriality to changes in these costs and benefits makes field experiments exceptionally feasible. Dr. Ewald will conduct the first rigorously controlled tests designed to resolve three fundamental, unanswered questions about agonistic behavior. First, he will assess the utility of controlled field experimentation by comparing the territorial responses to highly accurate but artificial energy sources with responses to the less-controllable natural energy sources. Second, he will test predictions about the existence of territoriality in relation to the net benefits obtained from the territory. Finally, he will determine whether or not the quality of the best alternative to territoriality influences the presence and/or form of territoriality. The areas of agreement and divergence between theoretical predictions and actual territoriality in this system should clarify the applicability of the cost/benefit approach to territoriality. More generally, by helping to develop the cost/benefit theory of agonistic behavior, this clarification should eventually improve our understanding of the interaction between internal and environmental influences on agonistic behavior across the entire animal kingdom, including humans.
