Photoperiodic control of budgerigar reproduction: circadian changes in sensitivity



Female budgerigars provided with nest boxes and exposed to male vocalizations were kept on light regimes involving 6 h of light and then a further 2 h of light starting 8, 12, 16, 17 or 18 h after the initial dawn. A higher proportion of females laid when the second light period started 6 h after the first one, than when it started earlier or later. That the effect was not due merely to the males vocalizing more on this light regime than on others was shown by substituting for the males taped vocalizations played during the light periods. It remains possible that females are more responsive to those vocalizations instead of/as well as to light at some points of the circadian cycle than others.