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.
Highlights
In any message, signals need to be successfully processed through either single or multiple channels to effectively convey information from senders to receivers [1]
Behavioural Displays Male S. parvus showed a large repertoire of visual displays
All displays were seen on a regular basis outside the period of focal sampling
Summary
Signals need to be successfully processed through either single or multiple channels to effectively convey information from senders to receivers [1]. Signal detectability depends on signal design, conditions of the environment, and the receiver’s sensory system [2], [3]. Additional sensory stimulation in the environment can cause information to be lost. In the case of acoustic communication, noise and transmission properties of the environment may shape the spectral and temporal structure of signals [4,5,6] as well as emphasize the role of signal efficacy in the evolution of animal signals [7]. Senders can increase signal efficacy by either avoiding areas of high noise [8], overriding environmental noise [9], adjusting their signal timing [10,11,12] or by using frequencies less masked by background noise [13],[14]. Signallers may use additional modes of communication to facilitate transmission [15],[16]
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