Spatial and spectrotemporal features of noise alter female responses to costly male signals in Cope’s gray treefrog (Hyla chrysoscelis)

Abstract In anuran choruses, where many males call simultaneously, females must identify attractive conspecific signals amid high levels of background noise. We tested whether spatial separation between signals and noise (spatial release from masking, SRM) and spectrotemporally correlated amplitude fluctuations in noise (comodulation masking release, CMR) influence mate choice behavior and help females maintain preferences for energetically costly calls under noisy conditions. Using two-alternative phonotaxis tests with Cope’s gray treefrogs ( Hyla chrysoscelis ), we measured response probability, the calling effort of chosen males, and response latency in the absence of noise and in six noise treatments that factorially varied the location of the noise and its amplitude modulation pattern. Signals and noise were either colocated or spatially separated, and noise envelopes either lacked modulations (unmodulated) or had modulations that were correlated (i.e., comodulated) or uncorrelated across the frequency spectrum. Females responded in nearly all trials, but selected stimuli with lower calling effort and took longer to choose in the presence of noise. Responses rates were lowest and latencies longest when noise was unmodulated and colocated with signals. Spatially separating noise from signals improved performance across all measures. Introducing amplitude modulations generally yielded higher response rates and shorter latencies, but the impacts of modulation on stimulus selection were more varied, and there was limited evidence that comodulation improved performance. These findings indicate that spatial and spectrotemporal features of noise impact female responses to costly male signals and highlight perceptual mechanisms that may shape the evolution of communication in acoustically complex social environments.