The influence of light wavelength on phase-dependent responsiveness of the photoperiodic clock in migratory blackheaded bunting

We investigated the phase-dependent effects of light wavelength on photoperiodic clock in the migratory blackheaded bunting. Two experiments were performed, employing a skeleton paradigm (6 hours light: 6 hours darkness: 1 hour light: 11 hours darkness; 6L: 6D: 1L: 11D) at 37+/-2 lux intensity. In the experiment 1, both 6 and 1 h light pulses were given at the same wavelength, 5 00 nm (green) or 650 nm (red). A group exposed to both pulses of white light served as control. In the experiment 2, the two light pulses were given at two different wavelengths, 6 h at 500 nm (green) and I h at 640 nm (red) in one group or vice-versa in the other. There was almost no photoinduction when both light pulses in experiment 1, or 1 h light pulse in experiment 2, were green. On the other hand, birds fattened and testes recrudesced when both the light pulses in experiment 1, or 1 h light pulse in experiment 2, were red. Birds receiving both pulses of white light in experiment 1 showed an intermediate response. Taken together, these results indicate that the photoperiodic clock in buntings is differentially responsive at its various circadian phases to different light wavelengths.