Stranger danger: acoustic response of the Veery (Catharus fuscescens) via heterospecific eavesdropping on the Tufted Titmouse (Baeolophus bicolor)

In this study I examined heterospecific eavesdropping in passerines by investigating how information broadcast by the Tufted Titmouse (Baeolophus bicolor) at dusk modifies singing and calling vocalizations of a common avian dusk chorus species, the Veery (Catharus fuscescens). The Veery nests on or near the ground and is a highly vocal participant of the avian dusk chorus, which also renders it vulnerable to a wide array of diurnal and crepuscular predators. Thus, the Veery is expected to be sensitive to signals of predation risk. Here, I report findings of simulated exposure to indirect predation risk (recorded playbacks of Tufted Titmouse alarm calls) that alter acoustic output by the Veery. From 19 May to 6 July 2013, 14 plots in Veery territories were selected and exposed to playback calls of the gray tree frog (Hyla versicolor; control treatment) and playbacks of the Tufted Titmouse high seet call (experimental treatment). Each plot was subjected to two 65 min playback-recording trials (one experimental and one control); Veery song and call output were quantified via spectrograms to compare Veery acoustic response between treatments. The Veery produced a greater call output while song output remained unchanged between control and experimental treatments. These results reveal that the Veery indeed detected and responded to heterospecific alarm calls. Moreover, the Veery acted as a secondary community informant, further transmitting information regarding predation risk to conspecifics and the dusk chorus community at large.