Cryptic Vocal Communication in the Proboscis Bat (Rhynchonycteris naso).

Cryptic-living animals face the trade-off between communicating effectively while avoiding detection. To examine how this trade-off shapes vocal behavior, we studied the vocal repertoire of the cryptic-living, neotropical proboscis bat (Rhynchonycteris naso; Emballonuridae). R. naso produces 22 syllable types and 17 vocalization types, including song. One common social vocalization type resembles modified echolocation calls and may also provide sensory information. Vocalizations shaped by natural selection appeared adapted to minimize predation risk: they are short, span broad frequency ranges, have limited detection ranges, and are mostly emitted during rocking, a behavior that maintains crypsis. In contrast, sexually selected vocalizations such as song are more conspicuous, highlighting a tension between effective signaling and remaining undetected. A phylogenetic analysis across 38 emballonurid bat species revealed that R. naso emits exceptionally high-frequency echolocation calls, beyond expectation from body size alone, and beyond the hearing range of most predators and prey, probably reflecting acoustic crypsis. The high-frequency echolocation calls of R. naso reduce detection distances for hearing moths and likely increase capture success. Overall, our study shows that R. naso employs diverse acoustic adaptations to communicate effectively while minimizing detection risk, offering rare insight into the evolution of vocal behaviors in cryptic species.