I have friend of mine that studies chicken behaviour up north. She told me once that it's not a lack of something in the diet per-say but does have a lot to do with content of diet. recent studies show those that are fed on diets which are either too low in mineral consumption, proteins, amino acid, or if when the diet only consisted of vegetables, are more susceptible to severe feather pecking.
But a diet which consists of high-fibre or a low-energy diet is said to reduce the pecking amongst your flock. As Chuck also mentioned boredom and space is a big factor and any diet changes that are made drastically can also make things worse. So if you do plan on changing anything do it gradually. Hence my questions in my previous post to know more about your situation to be able to help you better.