The signal in noise: Acoustic information for soundscape orientation in two North American tree frogs

Diverse animals use environmental sounds to orient in ecological soundscapes. Yet, we know little about how acoustic information use drives behavioral decisions to orient. Although the sound generated by frog choruses functions as noise that impairs signal reception by listeners in the aggregation, it can also serve as an informative ecological signal that allows other individuals to orient toward and localize active breeding aggregations. Here, we investigated the acoustic cues that elicit orientation toward the sound of a chorus in green tree frogs (Hyla cinerea) and Cope's gray tree frogs (Hyla chrysoscelis). We measured phonotaxis behavior of gravid females in response to playbacks of natural choruses and artificial choruses that differed in the types of acoustic information present. Females of both species oriented to natural choruses and to artificial choruses that contained information on the actual timing and temporal structure of individual calls embedded in the sound of the chorus. Artificial choruses with the time-averaged frequency spectrum and amplitude-modulation spectrum of natural choruses, but lacking information on the timing and temporal structure of individual calls, did not elicit positive phonotaxis. Our results indicate that temporal information from individual calls in the din of chorus sounds is necessary to elicit soundscape orientation. Because the temporal structure of individual calls may degrade quickly as the sound of the chorus propagates through the habitat, orientation to breeding choruses based on acoustic information alone may be limited to relatively short distances in these 2 species.