The Effects of Environmental Seasonal Changes on Eurasian Blackbirds (Turdus Merula) Plasma T3 (Triiodothyronine) and T4 (Thyroxine) Hormones

Abstract

This study was conducted in order to determine the effects of seasonal and daily temperatures on the levels of plasma thyroid hormone (T3 and T4) of Eurasian Blackbird (Turdus merula) among the different seasons. During the field studies carried out in Sarikum Sinop between 2017-2018, 48 T. merula were caught with mist nets, ringed and blood samples were taken for hormone analysis. It was found that thyroid hormone levels were affected by seasonal temperatures as a result of hormone analysis. According to our results plasma T3 and T4 hormone concentrations were changed in both morning and afternoon groups in autumn, winter, spring and summer seasons, and this situation was closely related to the reproductive period or moulting of T. merula while that seasonal varying temperatures affect the amount of these hormones. The dramatic temperature differences both seasonally and during the day were important factors in changing hormone levels.