Should receivers follow multiple signal components? An economic perspective

Lay Summary Animals often communicate with each other via elaborate displays. A popular hypothesis is that such displays somehow benefit the animals toward which communication is directed; however, theoretical optimality models usually predict that these animals should attend to the single "best" component of a display. This study supported the latter prediction, suggesting that additional benefits are required to explain the prevalence of complex communication in nature.Animal signals commonly consist of many components. Students of signaling have suggested that these complex, multicomponent signals are beneficial because they are more effective at influencing receiver behavior. This "more is better" view, however, is at odds with economic models, which predict that a single signal component is often sufficient to guide receiver behavior. This study develops a model that asks how receivers should respond to a simple 2-component signal. Our model predicts that receivers will follow the single most reliable component and ignore the second component. We tested this model experimentally using captive blue jays (Cyanocitta cristata) as experimental receivers. We presented receivers with artificial signals composed of 2 components and assessed their responses to determine which component(s) they followed. Signals were composed of 2 visual components: a color and a pattern. We tested 3 levels of color reliability and 3 levels of pattern reliability in a factorial combination, resulting in 9 total treatments. We found that subjects followed a single signal component at a high level in every treatment, whereas the second component had a nearly negligible effect. Subjects generally followed the more reliable component, though they showed a bias in favor of color when the reliabilities of color and pattern were similar. We argue that alternative receiver benefits need to be considered to explain the prevalence of complex signals in nature.