Neural control of singing in the dark-eyed junco (Junco hyemalis)

Abstract

This dissertation includes several discrete projects addressing various aspects of the neural control of singing in the Dark-eyed Junco (Junco hyemalis), a migratory songbird. I collected the birds from a local wild population during the breeding season and migration. Chapter 2 addresses the role of testosterone in controlling volumes of the brain regions that control song learning and song production (vocal control regions, VCRs), which grow and shrink seasonally and are correlated with changes in singing behavior. I found that: the role testosterone plays may depend on the age of the bird and the brain region in question. Expanding on that study, I investigated the independent roles of testosterone and photoperiod in the control of VCR volumes in adolescent male juncos (Chapter 3). In seasonally breeding species, circulating androgens increase with increasing photoperiod, so increases in VCR volumes in the spring had been thought to be a result of photoperiod-induced increases in testosterone. Experimental separation of photoperiod and testosterone revealed that long photoperiod alone can have stimulatory effects on VCR growth, despite low testosterone levels. In fact, in adolescent male juncos, lengthening photoperiod may play a greater role in determining VCR volumes than testosterone does, again suggesting that the role of testosterone in the vocal control system may change with age. Other neurochemicals besides testosterone are present in the vocal control system; Chapter 4 describes the first description of opioid peptide receptor localization and density measurement in the vocal control system of adult male songbirds. I expanded that study to include nonsinging female and juvenile juncos (Chapter 5). The results of the expanded study indicate that opioids may modulate development of the vocal control system between adolescence and adulthood, as well as auditory processing throughout life.