Avian Auditory Processing at Four Different Scales: Variation Among Species, Seasons, Sexes, and Individuals

Abstract

Previous research on songbirds has typically focused on variation in production of vocal communication signals. These studies have addressed the mechanisms and functional significance of variation in vocal production across species and, within species, across seasons and among individuals (e.g., males of varying resource-holding capacity). However, far less is known about parallel variation in auditory processing, particularly in non-model species. A relationship between vocal signals and auditory processing is expected based on the sender–receiver matching hypothesis. Here, we review our recent comparative studies of auditory processing in songbirds conducted using auditory evoked potentials (AEPs) in a variety of field-caught songbird species. AEPs are voltage waveforms recorded from the scalp surface that originate from synchronous neural activity and provide insight into the sensitivity, frequency resolution, and temporal resolution of the subcortical auditory system. These studies uncovered variation in auditory processing at a number of different scales that was generally consistent with the sender–receiver matching hypothesis. For example, differences in auditory processing were uncovered among species and across seasons that may enhance perception of communication signals in species-specific habitats and during periods of mate selection, respectively. Sex differences were also revealed, often in season-specific patterns, and surprising individual differences were observed in auditory processing of mate attraction signals but not of calls used in interspecific contexts. While much remains to be learned, these studies highlight a previously unrecognized degree of parallel variation in songbirds, existing at diverse hierarchical scales, between production of vocal communication signals and subcortical sensory processing.