Females expressed a preference for the typically more attractive call in the presence of unimodal noise. Robotic frogs were employed as either visual signal components (synchronous vocal sac inflation with call) or visual noise (asynchronous vocal sac inflation with call). We used natural calls from conspecifics and heterospecifics for acoustic noise. Noise treatments were partitioned into three categories: acoustic, visual, and multimodal. We tested female túngara frog, Physalaemus (=Engystomops) pustulosus, responses to male mating signals in noise from multiple sensory modalities (acoustic and visual). When sensory systems process input from multimodal signal sources, multimodal noise may arise and potentially complicate decision-making due to the demands on cognitive integration tasks. Some evidence suggests multimodal signals may not always improve receiver decision-making performance. Multimodal noise may arise, however, in dense aggregations of animals communicating via multiple sensory modalities.
We suggest that the vocal sac acts as a visual cue and improves detection and discrimination of acoustic signals by making them more salient to receivers amidst complex biotic background noise.įemales of many species choose mates using multiple sensory modalities. Multimodal stimuli elicited greater response from males and triggered significantly more visual signal responses than unimodal stimuli. Our results suggest that abiotic noise of the stream does not constrain signal detection, but males are faced with acoustic interference and masking from conspecific chorus noise.
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In the present study, we measured sound pressure levels of concurrently calling males of the Small Torrent Frog (Micrixalus saxicola) and used acoustic playbacks and an inflatable balloon mimicking a vocal sac to investigate male responses to controlled unimodal (acoustic) and multimodal (acoustic and visual) dynamic stimuli in the frogs' natural habitat.
The acoustic communication of anuran amphibians can be masked by the presence of environmental background noise, and multimodal displays may enhance receiver detection in complex acoustic environments. Many animals use multimodal (both visual and acoustic) components in courtship signals.