Noise output of hens subjected to interrupted lighting regimens.

1. Noise output from domestic hens subjected to an interrupted lighting regimen began before dawn of the apparent day. 2. Noise output did not cease during the scotoperiod(s) which interrupted the apparent day. 3. Differential noise outputs during the 30 min. 4 h and 10 h scotoperiods of a 1L:7(30D:30L):4D:2L:10D regimen indicated that the hen's interpretation of darkness, even within the apparent day, was complex and probably dependent on several factors. 4. Noise output data suggested that the intense feeding behaviour at the end of the apparent day, effected by the interrupted lighting regimen, appeared to prevent the pre-dusk reduction in activity observed in conventionally lighted birds. 5. Noise output was negligible during the scotoperiod which the hen interpreted as night.