  Using data of fast-rotating active dwarf stars in the Kepler database, we
perform time-frequency analysis of the light curves in order to search for
signs of activity cycles. We use the phenomenon that the active region
latitudes vary with the cycle (like the solar butterfly diagram), which causes
the observed rotation period to change as a consequence of differential
rotation. We find cycles in 8 cases of the 39 promising targets with periods
between of 300-900 days.
