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

Under continuous lighting, time of oviposition was controlled by a temperature cycle (12 h at 30 degrees C and 12 h at 20 degrees 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.