Roosting behaviour in laying hens on perches of different temperatures: Trade-offs between thermoregulation, energy budget, vigilance and resting
Laying hens usually select an elevated position for resting at night-time. A previous study showed that the position a hen takes during resting was affected by perch material, most probably due to its thermal conductivity. The aim of the present study was to analyse the effect of perch surface temperature on resting behaviour and resting comfort in laying hens. In each of two identical trials, three groups of five Lohmann Selected Leghorn hens were housed in each of three compartments in turn (n = 30 birds in six groups). Compartments were equally equipped with one smooth, round galvanised steel perch of 34 mm external diameter. The surface temperatures of perches were controlled by passing water through them, giving temperatures of 15 °C, 18 °C (room temperature) and 28 °C respectively in the three compartments. Hen behaviour was observed at night-time by investigating the proportion of active behavioural patterns and resting (standing or sitting), either with 'head forward motionless and neck withdrawn' or 'head tucked backwards into feathers above wing base or behind a wing.' The number of hens perching and the time spent perching were unaffected by perch temperature. Hens' resting postures, however, were strongly influenced. On the warmest perch, hens rested more with their head forward in a standing position and showed more active behavioural patterns compared to both cooler perches (P < 0.001). On the cooler perches, hens rested more with their head covered by feathers in a sitting and standing position (P < 0.05). Our data show that perch temperature strongly affects laying hens' resting behaviour. In this context, hens are confronted with arising trade-offs between thermoregulatory adjustment of behaviour, optimisation of energy budget, restful roosting and vigilance behaviour.