Meeting Abstract
The annual migrations of animals to their seasonal breeding grounds and back again has long been a topic of interest to researchers. However, studies examining the mechanisms controlling migration have been disproportionately focused on the vernal stage. As a result, we have begun to disentangle the complex system of environmental cues, neuroendocrine and endocrine systems responsible for the transition from the wintering to spring life history stages, yet, we know little about the processes controlling autumn migration. There is strong evidence from vernal studies supporting a major role for thyroid hormone action in the expression of vernal migration. Therefore, we predicted that T4 and T3 might also be involved in autumnal migration. Here we present the results of a chemical inhibition of thyroid hormone production by methimazole in captive white-crowned sparrows during the period prior to and during autumn migration in their free-living counterparts. Expression of the autumn migratory life history stage was assessed via physiological parameters of fat deposition, pectoralis muscle profile, and body mass, as well as recordings of locomotor nocturnal activity levels to determine the presence of migratory restlessness. Contrary to our prediction, we found that methimazole treated birds showed increases in body mass and fat scores; there was no discernible effect on nocturnal activity patterns. These observations stand in contrast to previous studies employing chemical inhibition of thyroid hormone production on vernal migration, which inhibited all aspects of the life history stage measured. Hormonal control of autumnal migration remains obscure, but these data indicate a broader approach to identifying potential mediators is necessary.
