BEHAVIORAL-RESPONSES OF HENS TO SIMULATED DAWN AND DUSK PERIODS

Behavioral responses to caged (3 birds by 6 cages) and aviary (437 birds) hens to sudden (S) and gradual (G) changes in illumination were recorded using an infrared camera. They were observed from 2 days before the change from S to G, to 7 days after the change. Each observation period commenced 30 min before the start or the end of the light period and ended 30 min after. In the battery cages, the number of birds standing increased gradually before the light period in both conditions. The number of birds eating peaked during the simulated dawn and dusk periods. Almost all birds (94%) were still standing during the 1st min of complete darkness under the S condition, but half of them (47%) were already sitting at the same time under the G condition. In the aviary, just after the S change from dark to light, the number of birds changing positions (between floors, etc.) increased sharply, but under the G condition the number increased gradually during the dawn period. The number of birds changing positions decreased immediately after the S change from light to dark, but some birds (2 to 3%) were still active shortly before the end of the observation period. However, most of the birds moved toward the resting site during the dusk period, and only a few birds (< 1%) were active 10 min after complete darkness. These differences were statistically significant (P < .05). The results of the present study indicate that a gradual change in illumination could be more comfortable for the birds.