Meeting Abstract

103.6  Tuesday, Jan. 7 09:30  Development of vernal migration and breeding stages in the White-crowned Sparrow (Z. Leucophrys gambelli): a role for thyroid hormones? PEREZ, JH*; WINGFIELD, JC; RAMENOFSKY, M; Univ. of California, Davis jhperez@ucdavis.edu

With the annual increase in photoperiod, migratory White-crowned Sparrows (Z. l. gambelii) undergo preparations for vernal migration and initiate preparations for breeding. The transition between wintering and these two stages requires major changes in physiology, morphology and behavior regulated by endocrine and neuroendocrine mechanisms, which are not completely understood. Previous studies have identified a potential links between thyroid hormones and the spring events associated with migration and breeding. Work by Nair et al. (1994) showed that surgical thyroidectomy abolished two characteristics of migration: spring fattening and nocturnal migratory restlessness. Building on this work, we are exploring the role of thyroid hormones (T3, T4) in additional spring events that include changes in flight muscle as well as gonadal development. In order to avoid potential complications of surgical excision or irradiation of the thyroid, the anti-thyroid agent Methimazole was delivered with subcutaneous silastic implants and oral administration. This drug reversibly inhibits thyroperoxidase, the enzyme responsible for conjugation and organification of T4. White-crowned sparrows were exposed to a naturally increasing photoperiod from early December to May 5th. Methimazole suppressed the following migratory traits: fattening, hypertrophy of the pectoralis muscles, a visual measure of fat accumulation within flight muscle, and pre-alternate molt. Additionally, testicular recrudescence was curtailed. Our findings suggest that the HPT axis is important for the coordination of key spring events regulating both development of migration and breeding in migratory songbirds.