Playback tests and studies of animal contest dynamics: concepts and an example in the gray tree frog

Animal contests can greatly impact individual fitness; therefore, the behavioral strategies used during contests have received much interest in both theoretical and empirical studies. Recent reviews of animal contest behavior have clarified the predictions for contest dynamics when individuals’ behavioral strategies are based on influences of self, opponent, or both. These predictions mostly apply to natural or staged interactions between 2 competing animals, but studies of aggressive signaling behavior often use other methodologies. In particular, playback tests have been heavily utilized because they provide the investigator with powerful control over experimental conditions. My aims in this paper are 2-fold. First, I discuss how playback tests can be used to study animal contest dynamics. Specifically, I develop predictions for individuals’ responses to playback tests that will allow investigators to discriminate between different contest strategies. By monitoring individual persistence, resource-holding potential (or its correlates as reflected in signal structure), and other behaviors in appropriately designed playback tests, I show that strategies based on influences of self, opponent, and both self and opponent can be discriminated. Second, I illustrate these methods with data from a playback experiment on male responses to acoustic signals in the gray tree frog, Hyla versicolor. Males’ responses to playbacks of synthetic advertisement and aggressive calls that varied in call frequency indicated that both self and opponent characteristics influenced persistence in contests.