Are you having much of a problem now or just trying to prevent a problem?
Levels can be created with things like platforms, tables, chairs, shelves, ledges and branches or roosts. Visual barriers are things that block their view. They act as room dividers. A piece of plywood that's vertical, bushes or a platform with some sides open and one or two sides covered. Even some of the things that add levels work to get the victim out of sight. Make sure you don't make a space where a victim will get cornered and trapped. Then should have a way out of any space you make.
Nice chickens do a little pecking order maintenance. Aggressive bullies can kill the victim. Chickens have very different temperaments. Some would never be a bully or a victim, no matter what the circumstances are. Some are prone to it in even the best conditions. I think most are in the middle somewhere. Sometimes a victim is just more passive and sometimes they're not healthy. Sometimes the bully is just an unusually mean and aggressive chicken.
Once you see blood drawn, you need to step in, as the victim is at a much higher risk of being killed. Up until then, I'd watch them. In a healthier situation, the more dominant chicken will peck at another, pull feathers or even chase a chicken away, then is satisfied. The more troublesome behavior is if a chicken won't let up and focuses on a victim constantly, hunting her down, no matter what she does or where she goes and wanting to draw blood. You can see how crowded, confined conditions make that an especially dangerous situation.
Anything that stresses chickens and makes them more agitated can cause bullying or make it worse. This can be a physical stressor, like external parasites, a diet that's not balanced and causing a slight case of malnutrition or something that's disturbing their sleep. It could also be something that makes the birds more anxious or worried, like being too crowded, changing the number of chickens in a flock, a new dog running around the outside of the pen or not having enough food. There are a lot of things that can contribute to it. Being crowded and bored is a bad combination in chickens that are more aggressive or high strung.
If you're having trouble with bullying, it's always good to look at your management practices, to see what may be contributing to the problem. Correct whatever isn't optimum. Things that help reduce bullying are more space, adding additional food/water containers, food to forage, activities to keep them busy, adding levels and breaking up the visual space, so the victim of the bully isn't constantly in sight. Sometimes it helps to take a particular bully out of the flock for a few days.
