Call variation and calling site preference of three sympatric Boulenophrys frogs.

Animals living in syntopy share acoustic space. Asian horned frogs are well known for their sympatric distribution, but little is known about their strategies to avoid acoustic niche competition. This study focused on three sympatric Boulenophrys frog species from southern China-B. nanlingensis, B. ombrophila, and B. shimentaina, with the former two species call in similar frequencies but breed in different seasons. First, we checked the call variation during the change of individual body size and the ambient air temperature in three species. We have found call frequencies were the most static parameters in each species that were associated with body size and contributed most to species identification. Temporal call parameters shift with temperature but are mostly influenced by low temperatures. Second, we checked the interactions between the environment and call properties. The calling site preferences of each species corresponded well with the prediction of the acoustic adaptation hypothesis (in view of higher frequency better transmission in open habitat), and species with similar call frequencies have some aspects of common calling sites. Third, we checked the species-species interaction by using playback tests with male B. nanlingensis. Results from playback experiments showed species that call at similar frequencies could hardly share the same habitat during the same season. These findings expanded the knowledge of acoustic coexistence in closely related anuran species and provided insights into the vocal behavior of Asian horned frogs.