The relative importance of light and temperature as phase setting signals for oviposition in the fowl

1. Under continuous lighting, time of oviposition was controlled by a temperature cycle (12 h at 30 °C and 12 h at 20 °C). The peak of egg laying occurred 15 h after the beginning of the cool period, which is the same interval as the interval observed between lights‐out and peak egg laying under a 12L : 12D lighting schedule.

2. When the temperature cycle was set 12 h out of phase with a light‐dark cycle (12L : 12D; temperature reduced when the lights came on), oviposition was entrained by the light‐dark cycle.

3. When a temperature cycle was set 6 h in advance or 6 h in arrears of a 12L : 12D cycle there was a difference of 1.4 h in mean time of lay between the two treatments, indicating that temperature can have a significant, though subsidiary, effect on oviposition time in the presence of a clear light‐dark signal.

4. When the light‐dark signal was reduced to 22L : 2D, oviposition time was controlled by the temperature cycle. With 20L : 4D oviposition time was determined principally by the photoperiod, but with a subsidiary effect due to temperature.