Effects of sex composition on fear measured as tonic immobility and vigilance behaviour in large flocks of laying hens

Abstract

Fear can be a damaging stressor, resulting in impaired animal welfare and poor production economy. Often fear reactions are elicited in situations that are in some way related to predator defence. As males have a guarding role, mixing the sexes might be a way of reducing fear in large groups of laying hens. Tonic immobility (TI) and vigilance are anti-predator behaviours shown by poultry. They have been used in several studies to measure the level of fear or stress. The influence of males on duration of TI, vigilance and total number of behaviour transitions in female laying hens was studied on an egg production farm. Eight groups of 1200 white LSL layers each were used and 25 focal birds in each group were studied. In half of the groups one male per 100 females was added. The presence of males had a significant effect on TI-duration and frequency and duration of vigilant behaviour (P<0.001); females in the mixed-sex groups had shorter TI-duration and showed less and shorter vigilance than females in the all-female groups. There was no significant effect on observed agonistic behaviour or the total number of behaviour transitions. However, significantly fewer females in the mixed groups had peck wounds on the comb. These results indicate that female laying hens show less signs of fear if the flock also contains males.