Zebra finch song reflects current food availability

Food availability is a major evolutionary force that has direct effects on an individual's body condition. Since sexually selected traits are often condition-dependent, they are likely to reflect food availability or other ecological constraints. Here we test whether bird song, which is thought to be under intense female choice, is sensitive to food availability and might be used by females to assess male body condition and/or territory quality. We manipulated food availability of male zebra finches (Taeniopygia guttata) and assessed the within-individual effects of the treatment on song parameters that are thought to be important in mate choice. We found no effect of food availability on syllable repertoire, proportion of sound versus silence within a song, and mean song frequency. In contrast, treatment birds showed a reduced song rate, an increased latency to sing, and a lowered song amplitude and fundamental frequency. Our study demonstrates that zebra finch song reflects food availability and that songs of well-fed males contain traits that have previously been reported to be more attractive to females. This adds strong support to the general assumption that female song preferences evolved because song reflects male quality and/or territory quality. Moreover, our study provides corroborative evidence for the notion that variation in environmental factors plays an important role in the evolution of mating signals.