Date of Award
Adult waterslager canaries produce the majority of their song under the control of the left hemisphere / left syringeal half. Unilateral section of the left treacheosyringeal nerve results in near complete loss of song while right denervation affects only a subset of call elements. This strong asymmetry for the production of a learned vocalization is reminiscent of the left hemisphere control for language in humans and provides a potentially powerful animal model to study lateralized behaviors in the vertebrate brain. ! Earlier work on another songbird, the European chaffinch, Friungilla crebes, suggested that the onset of lateralized vocalizations occured before song learning took place, but did not provide information about when and where this functional asymmetry first occurred. This â€œwhenâ€ and â€œhowâ€ became the focus of my thesis. ! In chapter 2, I describe the vocal ontogeny of begging calls in the canary, Serinus canaria. I describe the major call types, focusing primarily on two calls I named type A and type B. I show that the two calls are not interchangeable and are produced in different contexts as well as in different positions in the begging bout. Moreover, I show that B calls first appear as modifications of A calls and are mechanically produced differently by the bird. Using call structure analysis, I suggest that B calls may provide location information to parents, a suggestion that is supported by my finding that the emergence of B calls coincides with the time when young canaries leave the nest, which is referred to as â€˜fledging.â€™ ! In chapter 3, I performed unilateral denervations across begging call ontogeny and found that late, but not early begging calls are asymmetrically produced. I further show that this onset of asymmetric contributions to the begging call by the syrinx emerges suddenly across one day -the day B calls appear and birds fledge. Call analysis revealed that both A and B calls are affected and thus, fascinatingly, A calls, which are little affected by syringeal denervation before P15, fall asymmetrically under the influence of the left syringeal half at P16. Track tracing experiments reveal that the descending motor pathway for food begging in canaries projects ipsilaterally, suggesting that the left / right differences in vocal control observed at the level of the syrinx, mirror left / right differences in control that occur at higher brain areas. ! In chapter 4, I describe that food deprivation can shift the timing of fledging earlier. Furthermore, fledging earlier was accompanied by B call production and the onset of lateralized begging calls. The correlative emergence of these phenomena in stressed and unstressed canaries is striking and I propose that B calls serve a new communicative need that arises with leaving the nest -namely, locatability. The emergence of vocal lateralization when the bird leaves the nest, regardless of age at which it occurs, is also curious and I posit that if lateralization of function is a way of compartmentalizing the complex world, then perhaps laterality arises when this world is first met.
Bellani, Rudy, "Vocal Handedness: The Emergence of Lateralization at Fledging" (2012). Student Theses and Dissertations. 155.