Social organization in caged layers: the peck order revisited.

The dominance hierarchy that exists among free ranging chickens is a peck order. Several researchers have attempted to correlate various production parameters of caged layers with dominance rank, with mixed results. Animal welfare groups have expressed increasing concern over the effects of battery cage housing on the behavior of layers, even though several researchers have shown that the incidence of aggressive pecks decreases in these cages. The studies presented here demonstrate that agonistic interactions occur among most pairs of hens housed in pens but do not occur among most pairs of hens housed in cages. Therefore, peck orders could be constructed for hens housed in pens but not for hens housed in cages. Incidence of agonistic interactions is highest in cage-housed hens immediately following housing of the hens; this peak is matched when group membership is mixed. These results suggest that a social system does form among caged hens even if a peck order does not. A single dominant hen in each cage was involved in and won a large majority of the agonistic encounters in the cages. The lack of evidence of dominance relationships between pairs of hens in cages, other than those between a single dominant hen and its cage mates, supports the hypothesis that despotism, not a peck order, was the prevailing social organization among hens housed in high-density cages.