Early-life stress affects song complexity, song learning and volume of the brain nucleus RA in adult male song sparrows

The developmental stress hypothesis proposes that the honesty of birdsong is maintained by costs incurred during development, such that song in adulthood reflects exposure to early-life stressors. We determined the effects of early-life (7–60 days of age) food restriction or corticosterone (CORT) treatment on adult song production and neuroanatomy in male song sparrows, Melospiza melodia. When males were adults, we quantified song type repertoire size, syllable repertoire size, song-learning accuracy, trill deviation (the speed of frequency modulation in a trill) and song type stereotypy. We also analysed the volumes of the song control nuclei HVC, the robust nucleus of the arcopallium (RA), area X and the number of neurons in HVC. Song type and syllable repertoire sizes of food-restricted and CORT-treated birds were smaller than those of controls. Food restriction, but not CORT treatment, also reduced song-learning accuracy. We observed no effects of either treatment on trill deviation or song type stereotypy. However, trill deviation was significantly related to paternal repertoire size, suggesting a heritable component to some aspects of vocal learning. The volume of RA was smaller in food-restricted birds than in control or CORT-treated birds. Neither treatment affected the volumes of HVC or area X, or the number of neurons in HVC. Our results suggest that song complexity and song-learning accuracy may be honest indicators of a male song sparrow's early ontogeny and that early-life stress has long-lasting effects on the song control system in this species. However, measures of vocal performance (trill deviation, song type stereotypy) do not appear to be significantly affected by early-life stress in song sparrows.