Behaviour 2019
The use of bimodal acoustic signals by red-eyed treefrogs, Agalychnis callidryas
Michael S. Caldwell1,2, Kayla A. Britt1, Lilliana C Mischke1, Hannah Collins1,3. 1Gettysburg College, Gettysburg, PA, United States; 2Smithsonian Tropical Research Institute, Panama City, Panama, Panama; 3 University of Connecticut, Storrs, CT, United States

Airborne calls and songs have shaped our understanding of animal communication. Calling from vegetation or the ground also inevitably excites vibrations in those substrates, and air- and substrate-borne call components can function together as bimodal acoustic signals. Such signals have received little research attention, particularly among vertebrates. I used bimodal playbacks to test whether the advertisement call of red-eyed treefrogs functions as a bimodal signal. Both during mate choice and in agonistic interactions, the substrate vibration component substantially alters receiver responses to this signal. Females choose bimodal calls more than twice as often as unimodal air-borne calls. Similarly, males respond to bimodal playback with a greater number and variety of aggressive behaviors. These results indicate that red-eyed treefrogs, previously assumed to produce purely airborne calls, communicate with bimodal, sound and vibration, signals. As selection on either component will shape the evolution of such signals, it may be wise to reevaluate well studied communication systems to determine whether receivers attend to previously unstudied components of acoustic calls.