Female zebra finches prefer high-amplitude song

The intensity of a signal is crucial for animal communication because a high signal-to-noise ratio improves signal reception. However, variation in amplitude may also have signalling value. In songbirds, song amplitude varies considerably between males but little is known about the causes and consequences of this variation. One of the main functions of birdsong is mate attraction, but whether and how amplitude variation (beyond reception thresholds) affects female choice at all is poorly understood, as this parameter is notoriously difficult to measure in the field. However, levels of signal amplitude at the source and at the receiverʹs end can be reliably controlled under laboratory conditions. Here we addressed the question whether differences in male song amplitude may influence female choice. Song preferences of female zebra finches, Taeniopygia guttata, were tested in an operant conditioning task involving sets of four song stimuli, in each case derived from one original song. Within a set, stimuli differed in amplitude or in level of degradation but not in song phonology or syntax. We found that females preferred songs with higher sound pressure level within the tested range of naturally observed amplitude variation regardless of the two reverberation levels. As song preferences are highly predictive of mate choice in this species, our results suggest that female zebra finches may use song amplitude as a criterion in mate choice. This raises the question what information the naturally occurring variation in amplitude between males in this and other songbird species conveys about the singer.