Vigilance and roosting behaviour of laying hens on different perch heights
Laying hens prefer roosting on high compared to low perches during night time. According to the antipredator hypothesis, hens on high perches can afford to be less vigilant while roosting at night. A total of 120 LSL hens in groups of five were presented a single perch, which was varied in height throughout two subsequent experiments each. In experiment 1, an acoustic noise was played back in the middle of the night. Hens’ latencies until reaction and their roosting behaviours shown before disturbance were analysed depending on perch height (30, 90, or 150 cm). In addition, roosting behaviours were recorded throughout the entire experimental nights and differences were analysed in relation to perch height. Experiment 2 focussed on night-time use of single perches offered at ten different heights ranging from 20 cm to 180 cm. In experiment 1, perch height and hens’ body orientation towards the source of acoustic noise did not influence reaction latencies (P > 0.05). Surprisingly, hens resting with their head forward immediately before playbacks showed a slower reaction (LS-means = 1.27 s) to the acoustic noise than hens resting with their head under the wing (LS-means = 0.71 s, P = 0.004). In contrast, the percentage of hens perching with their head forward during the entire night was higher on low (LS-means = 55.48%) compared to high perches (LS-means = 33.44%, P = 0.001) in experiment 1. In both experiments, perch use increased with rising height up to 90 cm. In experiment 2, hens did not show a preference for roosting on the perch compared to resting on the floor at a perch height of 80 cm or lower. Although hens showed a clear preference to roost on perches higher than 90 cm, their reactions to an acoustic disturbance during night time did not clearly support the antipredator hypothesis. Possibly, perch height may be a crucial factor when hens are searching for an appropriate roosting place before the dark period but may have limited influence on roosting behaviour during the night.