DEVELOPMENT OF POSTHATCHING MELATONIN RHYTHM IN ZEBRA FINCHES (POEPHILA-GUTTATA)

We examined levels of melatonin in the pineal, eyes and plasma over a 24 h period during development in the altricial zebra finch. Beginning as early as 2 days after hatching there was a distinct 24 h rhythm in melatonin in the pineal and plasma. Beginning at day seven after hatc hing there was also a 24 h rhythm present in the eyes. In the pineal a nd eyes the amplitude of the 24 h rhythm increased with age. Tn contra st, the amplitude of the plasma melatonin rhythm at 2 days was already within the range of adults and did not increase with age. These resul ts confirm and expand earlier findings in the European starling and pa rallel those from precocial birds indicating that the circadian system is already competent at or shortly after hatching even in atricial bi rds.