Wavelength of light mimics the effects of the duration and intensity of a long photoperiod in stimulation of gonadal responses in the male blackheaded bunting (Emberiza melanocephala)

In male blackheaded bunting, we have investigated whether stimulatory effects of the duration and intensity of a long photoperiod can be mimicked by the wavelength of light used. The growth and development of testes, considered as the index of the photoperiodic effects, were examined at periodic intervals over a period of seven weeks. Two light wavelengths, one short (blue, 450 nm) and the other long (red, 650 nm), were used in different combinations of photoperiod and intensity in two sets of experiments, In the first set of experiments, the gonadal response to a 14 h photopezriod of blue light (14L:10D; L = 0.241 W/m(2)) was compared with that to a 12 h photoperiod of red light (12L:12D; L = 0.057 W/m(2)). The second set of experiments was identical to the first, except that it used high intensity of light (14L:10D, L-blue light = 1.46 W/m(2) 12L:12D, L-red light = 0.219 W/m(2)). There was a similar photoperiodic induction of testicular growth under two different lighting conditions in both sets of experiments. This clearly suggests that long light wavelengths mimic the effects of the duration and intensity of a long photoperiod in stimulation of gonadal responses in the male blackheaded bunting (Emberiza melanocephala).