They can be. Birds housed together need to establish a pecking order and chickens at the bottom of the hierarchy will suffer attacks from other birds. However, they usually stop short at eating each other. Pecking is such a central part of a chicken's behaviour that "toe-picking" of their own and other bird's feet is a common problem and can cause serious injuries. The theory is that their feet look a little like tasty worms. Eating bits of each other and themselves could be a sign of a deficiency in their diet. All animals will seek what they are lacking driven by an unconscious understanding of their bodily needs. Boredom is another agreed cause of cannibalistic behaviour in chickens. Chicks can be vulnerable to attack. Commercial chicken farms have resorted to automatic beak trimming which supporters of animal rights consider to be cruel. Domestic keepers of hens are encouraged to try and rule out possible causes before taking such steps.
