Light flashes of different durations (0.063-3.33 msec) phase shift the circadian flight activity of a bat.

The phase-response curve (PRC) for the circadian rhythm in the flight activity of a cave-dwelling bat, Hipposideros speoris, constructed with 0.063-msec light flashes, reported here is the first of its kind for any circadian system and is unlike any other phase-response curves constructed for other nocturnal animals. The phase responding with maximal advances (90 degrees) and the phase responding with maximal delays (0 degree) of this PRC were exposed to light flashes of systematically varying durations from 0.083 to 3.33-msec. For 0 degree phase, the flashes of 0.063-3.33 msec effected delay phase shifts of comparable magnitude. For 90 degrees phase, the flashes of 0.063-1.0 msec effected advance phase shifts, whereas 3.33-msec flashes effected unmistakable delay phase shifts with advancing transients. Phase shifts evoked with such light flashes are further compared with phase shifts evoked with pulses of longer durations (15 min to 2.8 hr) for H. speoris.