Print PagePredation is an important ecological cost of communication in animals and is thus a potent source of selection on signaling behavior. Heterospecific eavesdropping by predators may increase the vulnerability of actively vocalizing prey, particularly at dusk when nocturnal predators are hunting while songbirds are singing in the dusk chorus. Despite the risk it entails, dawn and dusk chorusing is common among diurnal songbirds. Here, we report the first demonstration of simulated predation risk altering the dusk chorus of a diurnal songbird, the veery (Catharus fuscescens). Veeries have a pronounced dusk chorus, singing well past sunset and potentially exposing themselves to predation by owls. We simulated increased predation risk by playing recordings of barred owls (Strix varia) to 24 veeries, and then compared the dusk chorus behavior of focal birds during this treatment with dusk singing recorded during control trials in which we either played recordings of gray tree frogs (Hyla versicolor) or played no recordings at all (silent).
Results/Conclusions
In response to a series of short playbacks (< 1 min) of owl calls, veeries sang a dusk chorus that included fewer songs overall relative to frog playback and silent control trials. In addition, veeries ended their dusk chorus up to 9 minutes earlier during owl playback trials: only 0.78 percent of songs in owl trials occurred after minute 39 compared to 5.17 percent for control trials. Our study indicates that veeries eavesdrop on the communication of potential predators and reduce their singing in the perceived presence of owls. Heterospecific eavesdropping is common in predator-prey systems, but is little examined in the case of singing in diurnal songbirds. Our study suggests that, for songbirds, there are fitness costs of singing in the low light of dusk, and that the dusk chorus may reveal a strong influence of predation risk on the evolution of singing behavior.
