Noisy Neighbors: Acoustic Interference and Vocal Interactions between Two Syntopic Species of Ranid Frogs, Rana clamitans and Rana catesbeiana

American Bullfrogs (Rana catesbeiana) and Green Frogs (Rana clamitans) share ranges and breeding seasons, are ecologically similar, and often occupy the same breeding ponds throughout the summer. Males of both species use vocalizations to defend territories and attract females; however, Bullfrogs have longer calls and call much more frequently than Green Frogs. The calls of the two species overlap in frequency; thus, Bullfrog calls are a likely source of acoustic interference for Green Frogs that could affect their ability to attract females. Nevertheless, in natural settings where these species co-occur, Green Frogs reproduce successfully. This suggests that Green Frogs respond to the calling patterns of Bullfrogs in ways that maximize Green Frog signal-to-noise ratio. We used long-term pond environment recordings and bioacoustics analyzing software to explore the influence of Bullfrog calling patterns on the vocal activity of syntopic Green Frogs. We found both species call most actively within the same seasonal and diel periods. Our results show that Green Frogs avoid overlapping their calls with Bullfrogs more often than expected by chance. Therefore, to avoid Bullfrog call overlap, Green Frogs use the fine-scale behavioral response of placing their calls in silent gaps between the calls of Bullfrogs. This pattern was even more pronounced in interactions between nearest neighbors in which there was no overlap observed between Bullfrogs and their nearest neighbor Green Frog.