A role for thyroid hormones in the development of premigratory disposition in redheaded bunting, Emberiza bruniceps

摘要: Excessive fat deposition and zugunruhe (nocturnal restlessness), two characteristics of premigratory disposition, are displayed in caged redheaded buntings. In earlier experiments thyroid ablation was found to inhibit fattening this bird. Also, seasonal investigations on hormonal profiles indicated a distinct rise circulating tri-iodothyronine just before spring migration, most likely as result increased peripheral monodeiodination thyroxine. The physiological relevance these findings has been assessed the present paper. Results that removal gland completely prevented development deposition; replacement therapy with T4 or T3 restored both. Thyroxine-induced thyroidectomized birds be dose responsive. intact each suppression extrathyroidal conversion thyroxine into triiodothyronine by iopanoic acid suppressed well birds, arguing for role migratory physiology. Blockage conversion, however, did not suppress feather regeneration, indicating unlike effects parameters same individuals thyroxine-induced regeneration does involve prior triiodothyronine. Thus, contrary prevailing view alone is finally active hormone (thyroxine being precursor), both may have specific roles play physiology events, one devices ensure energetically incompatible events like migration moulting do occur simultaneously. also indicate increasing daylengths which known trigger avian influence possibly imparting process an adaptive value timing events.