Accuracy of song syntax learning and singing consistency signal early condition in zebra finches

Abstract

Birdsong is a sexually selected and culturally transmitted multidimensional signal. Sexually selected traits are generally assumed to indicate condition. In oscine songbirds, song is learned early in life. The developmental stress hypothesis proposed that poor early developmental condition can adversely affect song learning. The quality and accuracy of learned song features could thus indicate male quality to conspecifics. Surprisingly, studies testing this hypothesis to date mostly compared adult males’ song repertoires without looking at song imitation. The few that did reported inconsistent effects and analyzed a limited number of song features. Here, we examined the effects of early condition (by brood size manipulation) on learned song in zebra finches, Taeniopygia guttata, in comparing both the number of specific elements copied from an adult song tutor and a great number of previously neglected syntax-, complexity-, and performance-related song features. The treatment did not significantly affect average number of imitated elements, the standard measure of quality of song imitation in this species. However, developmental condition had 2 significant main effects on adult song: birds from large broods (i.e., of poor early condition) in comparison to birds from small broods copied syntactical dependencies of song elements from the song motif of their tutor less accurately and had less consistent sound duration between song motifs. These findings support the developmental stress hypothesis. We discuss how this sheds light on the potential role of such long-term signals of male developmental condition in female mate choice and potential constraints underlying condition-dependent expression of song features.