There are a number of reasons why “pecking” may occur, with the most common being a lack of adequate space. Bored chickens, for some weird reason, peck each other. Once they’ve raised blood, it turns into a very bad thing, as it can get to the point where they will mortally injure another bird (the color red encourages pecking for some reason.)
The first thing to do if this starts, is to increase the amount of space available for your birds. The smallest must have enough room to run to get away from the bully.
The second thing to do is, make sure they’re not bored. Provide them with interesting things to do. If you can, let them day range or free range (if possible.) We use electric poultry netting to confine our birds, and it works very well for us.
If you must keep them cooped up, provide them with distractions. Some hay to peck apart, a head of lettuce to peck at, some scratch grain tossed in the bedding to find, all can help. But ideally, chickens should have access to grass and the outdoors, with lots of room to roam. A bored chicken is a bad chicken…
The other thing to look at is, are they pecking because they are plucking feathers from each other to eat? What are you feeding your birds? What is the protein level? Are you adding things in which could be lowering the level of protein? Inadequate protein levels can sometimes lead to feather plucking, which can lead to pecking.
Let us know a little more about what you're feeding and how your chickens are housed and we'll see if we can do more to help.
