Fig. 4. Effects of RU486 treatment on locomotor activity (hops min^-1) in spring migrants and in wintering birds. Locomotor activity was determined with motion detectors in registration cages and was investigated during three periods of the day: early-day, late-day and night. In response to treatment, locomotor activity changed similarly in controls and in RU486-treated birds during all examined periods. Locomotor activity is shown before and after RU486 injections. Sample size is indicated. Error bars represent S.E.M.