Role of Light in the Photoperiodic Responses of Migratory Birds

Science  22 May 1959:
Vol. 129, Issue 3360, pp. 1425-1426
DOI: 10.1126/science.129.3360.1425


Light-dark cycles with 12-hour and 16-hour photoperiods are known to be effective in 24-hour cycles in inducing gonadal activity and fat deposition in migratory birds. Twenty-four-hour cycles with 16-hour dark periods are not effective. To test the role of the light periods and the dark periods in a given cycle, slate-colored juncos were subjected to light in cycles which combined stimulatory photoperiods (L) and inhibitory dark periods (D) as follows: 12L-16D; 12L-20D; 16L-16D; 16L-22D; 16L-32D. The results indicate that the photoperiod, not the dark period, determined the response.