Environmental and hormonal control of vernal migration in redheaded bunting (Emberiza bruniceps)

摘要: This paper reviews the factors and mechanisms which result in development of metabolic state characteristic migration with special reference to a palaeotropic migrant redheaded bunting, Emberiza bruniceps. Changes climatic conditions food supply act as proximate triggers migratory behaviour partial migrants. Typical migrants like buntings use daylength cue but exact mechanism how photoperiodic information is translated terms events still not known. Almost entirely effects have been explained on basis involvement hypothalamo/hypophyseal system. We feel mechanism(s) other than those acting through neuroendocrine system may be equally important. Furthermore role temperature has adequately explored so far. Our observations indicate possibility that might integrate received from photoperiod environmental (and factors?) resulting state. The physiological control avian much less understood. Majority papers centered around 'gonadal hypothesis' Rowan supporting or contradicting it without providing conclusive evidence. Pituitary prolactin also shown implicated although action only speculative. Conclusive evidence for thyroid hormones (thyroxine, T4; triiodothyronine, T3) timing produced attributing independent roles T4 T3. It suggested seasonal variation peripheral conversion T3 could serve an effective strategy render available required and/or during different phases year thus accounting switch over T4-dependent moult T3-dependent fat deposition zugunruhe ensuring preclusion simultaneous occurrence these mutually incompatible events. Considering number influence this considering hormone molecule put wide range usage course evolution T4-T3 assume great flexibility selective value-especially known evolved several times diverse families. attractiveness hypothesis lies fact potential explain both at same time respect cycle environment conflicting (moult reproduction).