Circadian control of photoperiodic responses in a female migratory bunting (Emberiza bruniceps).

The photoperiodic response of female redheaded bunting (Emberiza bruniceps) was investigated in photosensitive and photorefractory birds exposed to resonance lighting cycles. Ovarian growth was stimulated in resonance cycles where light was present during the predicted photoinducible phase. Photorefractoriness was dissipated by resonance cycles in which light did not fall at times corresponding to the photoinducible phase. It is concluded that photosensitive and photorefractory female redheaded bunting monitor the photoperiodic time by means of a circadian rhythm.