Meeting Abstract

P3.81  Monday, Jan. 6 15:30  Does thyroid hormone T3 correlate with maximal thermogenic capacity in small passerines wintering at northern latitudes? MILBERGUE, M.*; CORTES, P.A.; BLIER, P.; VEZINA, F.; Univ. du Quebec à Rimouski, CEN, BOREAS, CSBQ myriam.milbergue@live.fr

In small passerine birds wintering in cold climates, maintenance of body temperature is achieved through physiological adjustments leading to improvement of heat production capacity. Cold acclimatization is associated with an increase in metabolic performance where basal metabolic rate (BMR) and maximal thermogenic capacity (Msum) are elevated during the cold season. Changes in these parameters are often interpreted as reflecting changes in mass or activity of internal organs. However, variation in organ mass only explains part of the variability in metabolic performance, likely because animals can also modulate tissue metabolic intensity. Thyroid hormone triiodothyroxine (T3) is known to increase in response to cold temperatures and to stimulate basal thermogenesis in birds, which suggest that basal levels of heat production may be modulated in response to cold. However, the potential effect of T3 on maximal thermogenic capacity is unknown. We studied a free-living population of black-capped chickadees (Poecile atricapillus) where more than 100 birds were captured several times over a complete winter to measure their BMR, Msum and plasma T3 levels. Samples are currently being processed. We are expecting positive correlations between T3 levels and both BMR and Msum at the level of the population and within individuals.