THE DUSK ORIENTATION AND THE INFLUENCE OF SUCCESSIVE TESTS ON PIED FLYCATCHERS (FICEDULA-HYPOLEUCA) TESTED IN EMLEN FUNNELS

Pied flycatchers were tested twice at sunset under a clear sky, a clea r sky with moon, and under artificial overcast conditions. The mean sp ring direction was W-NW, with a higher westward bias than in previous rests performed in complete darkness. The activity of single tests was high but their directionality was low, with an inverse correlation be tween activity and directionality. Under clear skies (with or without moon) the distribution of birds performing a rest for the first or sec ond rime was not different, with high consistency of individual birds, while in overcast conditions second tests shifted southwards, seeming ly a phototactic reaction. Under clear skies (with and without moon), in the second test individual vector lengths increased and there was n o correlation between individual activity and vector value, indicating an improvement of the performance; in contrast, in second overcast te sts vectors tended to decrease and the negative correlation activity/v ector was significant. So, although the mean direction was not differe nt from the clear sky, the individual performance was worse in overcas t conditions, probably due to a decrease in motivation to migrate duri ng prolonged overcast conditions.