Diurnal cycles of melatonin in bird pineal bodies

1. 1. Diurnal cycles of change in amounts of presumptive melatonin in the pineal bodies of three species of African weaver birds and the Japanese quail have been characterized. 2. 2. Melatonin is present in greater amounts during the dark phase than during the light phase of a 24-hr cycle. 3. 3. The phasing of the cycle with respect to real time and, to some extent, the form of the cycle are dependent upon the times and durations of the light and dark portions of photoperiods.