Injurious feather pecking is a major welfare problem in laying hens which can occur in all systems and is considered an abnormal behaviour. The causes are multi-factorial, including genetics, environment, health and management; however insufficient opportunity to carry out foraging behaviour is widely accepted as a primary factor(Huber-Eicher and Weschler, 1997).
Aggressive pecking, which is usually directed at the head, or allogrooming are not considered in this context. Feather pecking can be gentle (low frequency aimed at the plumage or stereotyped high frequency aimed at the tail feathers), or severe, causing denuded areas in the plumage with the potential of leading to skin wounds, vent pecking and cannibalism (Savory 1995).
Usually, a small number of hens in a flock initiate feather pecking, but its transmission throughout the flock is rapid via social facilitation.