Body condition and acoustic noise modify female responses to uni- and multimodal signals emitted by a male-mimicking robot frog

Mate choice is shaped by both intrinsic and extrinsic factors, including signal conspicuity, receiver body condition, and environmental properties. Multimodal signals are generally more conspicuous than unimodal ones and are expected to elicit stronger responses. However, variation in body condition and background noise modulate receivers’ responsiveness. We investigated how signal type (uni- or multimodal) interacts with body condition and background acoustic noise to influence female responses to male displays in the stream-breeding frog Crossodactylus schmidti. In a field experiment using a male-mimicking robot frog, females were exposed to acoustic (advertisement calls), visual (toe flags), and multimodal (advertisement calls + toe flags) stimuli, while their behavioral responses, body condition, and environmental acoustic noise were recorded. Females responded preferentially to multimodal stimuli over acoustic or visual ones. Those in poorer body condition were more responsive overall, reacting more readily to all stimulus types, indicating condition-dependent mate choice. High levels of acoustic noise generally reduced responses to visual signals, suggesting cross-modal sensory interference. However, when exposed to unimodal acoustic stimuli in noisier sites, females increased their visual signaling, possibly as compensatory behavior in response to auditory masking. These findings highlight the adaptive significance of multimodal signals in noisy environments and emphasize the role of female condition and background noise in shaping intersexual communication during mate choice.