Food intake and oviposition by domestic fowl under symmetric skeleton photoperiods.

1. Under a symmetric skeleton photoperiod of 2 h light, 10 h dark, 2 h light and 10 h dark (2L : 10D : 2L : 10D), most ovipositions occurred in the first 10-h dark period with an important mode during the first hour of darkness. 2. With a gradual increase of the first dark period (the period of activity), the ovipositions become increasingly spread throughout the 24-h cycle; a complete phase shift for the timing of oviposition was observed with the programme 2 h light, 11 h 15 min dark, 2 h light and 8 h 45 min dark (2L : 11.15D : 2L : 8.45D). 3. With the photoperiod 2L : 10D : 2L : 10D, the servicing of the birds during either 2-h light period, and the withdrawal of calcium source during either the second 2-h light period or during the first 10-h dark and second 2-h light periods did not change the timing of ovipositions.