Seasonal patterns of neurogenesis in European starlings (Sturnus vulgaris) are region- and sex-specific.

Songbird vocal behavior, physiology, and brains-including neurogenesis-change between seasons. We examined seasonal differences in neurogenesis in three brain regions associated with vocal production and learning, HVC (letter-based proper name), robust nucleus of the arcopallium (RA), and Area X, and two brain regions associated with auditory perception, caudomedial nidopallium (NCM) and caudomedial mesopallium (CMM). To do this, we captured wild male and female European starlings (Sturnus vulgaris) in spring and fall, collected a blood sample, and minimized time from capture to tissue collection to limit suppressive effects of captivity on neurogenesis. We quantified neurogenesis using doublecortin (DCX) immunohistochemistry, counting new neurons of three DCX cell morphologies (multipolar, fusiform, and round). We found regional differences in types of morphologies expressed, and amount of neurogenesis across regions: NCM had more fusiform cells than all other regions, and RA had more round cells than other regions. Males had more neurogenesis in HVC in fall than in spring, but there was no seasonal difference in neurogenesis in HVC of females, perhaps reflecting sexually dimorphic vocal learning demands related to repertoire size and complexity. Plasma corticosterone was higher in spring than fall and was correlated with testis volume in males, but it was not correlated with another purported measure of stress, heterophil:lymphocyte ratio (HLR), nor with neurogenesis. Our results suggest that the addition of new neurons to specific regions and circuits may serve different functions for males and females, particularly in the context of vocal production, learning, and perceptual demands across seasons.