MELATONIN IS CRUCIAL FOR THE MIGRATORY ORIENTATION OF PIED FLYCATCHERS (FICEDULA-HYPOLEUCA PALLAS)

After pinealectomy, young pied flycatchers tested in the geomagnetic f ield have been found to be disoriented. In order to examine the possib le role of the pineal hormone melatonin, handraised flycatchers were p inealectomized (PX) at the age of 8 weeks. From the day of operation o nward, the PX(MEL) group received 100 mu g of melatonin every evening 1 h before darkness, the PX(SOL) group was injected with the solvent o nly, and the PX group was untreated. Unoperated birds served as contro ls. During the following autumn migration, the birds were tested for d irectional preference in the local geomagnetic field, in the absence o f visual cues. The controls were oriented in the species-specific sout hwesterly direction; pinealectomized birds without additional melatoni n (PX(SOL), PX) did not show directional preferences. The PX(MEL) bird s that had received daily injections of melatonin also showed signific ant southwesterly tendencies; their orientation did not differ from th at of the controls. This indicates that melatonin is involved in migra tory orientation, either in the processes of expressing the geneticall y encoded information on the migratory course as a direction with resp ect to the geomagnetic field or in the time programme controlling the specific migratory direction at a given time.