Song Learning, Early Nutrition and Sexual Selection in Songbirds

SYNOPSIS. The developmental processes through which songbirdsacquire their species—typical songs have been well—studiedfrom a proximate perspective, but less attention has been givento the ultimate question of why birds learn to sing. We presenta new hypothesis for the adaptive significance of song learningin songbirds, suggesting that this specialized form of vocaldevelopment provides an indicator mechanism by which femalescan accurately assess the quality of potential mates. This hypothesisexpands on the established idea that song can provide an indicatorof male quality, but it explicitly links the variation in songexpression that females use to choose mates to the developmentalprocesses through which song is acquired. How well a male sings—reflectedin repertoire size or in other learned features of a male'ssinging behavior—provides an honest indicator of qualitybecause the timing of song learning and, more importantly, thetiming of the development of brain structures mediating learningcorresponds to a period in development during which young songbirdsare most likely to undergo nutritional stress. This correspondencemeans that song learning can provide a sensitive indicator ofearly developmental history in general, which in turn reflectsvarious aspects of the phenotypic and genotypic quality of apotential mate.