Multimodal Communication in a Noisy Environment: A Case Study of the Bornean Rock Frog Staurois parvus

TLDR

High background noise impedes signal detection and perception. The study reports how Staurois parvus uses multiple acoustic and visual strategies to improve signal perception in noisy environments. Acoustic playback experiments tested the efficacy‑based alerting signal hypothesis of multimodal communication. The frogs’ calls were not impaired by fast‑flowing water noise, with males adjusting amplitude, pitch, rate, and duration to maintain an 8‑dB advantage, and they also employed multiple visual signals such as foot flagging, foot flashing, arm waving, and posture changes, demonstrating a multimodal strategy that solves broadband low‑frequency noise.

Abstract

High background noise is an impediment to signal detection and perception. We report the use of multiple solutions to improve signal perception in the acoustic and visual modality by the Bornean rock frog, Staurois parvus. We discovered that vocal communication was not impaired by continuous abiotic background noise characterised by fast-flowing water. Males modified amplitude, pitch, repetition rate and duration of notes within their advertisement call. The difference in sound pressure between advertisement calls and background noise at the call dominant frequency of 5578 Hz was 8 dB, a difference sufficient for receiver detection. In addition, males used several visual signals to communicate with conspecifics with foot flagging and foot flashing being the most common and conspicuous visual displays, followed by arm waving, upright posture, crouching, and an open-mouth display. We used acoustic playback experiments to test the efficacy-based alerting signal hypothesis of multimodal communication. In support of the alerting hypothesis, we found that acoustic signals and foot flagging are functionally linked with advertisement calling preceding foot flagging. We conclude that S. parvus has solved the problem of continuous broadband low-frequency noise by both modifying its advertisement call in multiple ways and by using numerous visual signals. This is the first example of a frog using multiple acoustic and visual solutions to communicate in an environment characterised by continuous noise.