My Polish bantams easily cleared a six foot fence as soon as they had a few flight feathers. They did it from almost right below it, flew almost straight up. I wouldn't have believed it if I hadn't seen it. As soon as one did it, the others followed. I had them in the new run while we worked on it, thinking they would be more interested in the newly available grass while we put the top fencing on. I now trim flight feathers on one wing in the summer when they free range, because they really enjoy being up high. We have a fully enclosed run because of predators, but quite a few of our bantams of various breeds are very good fliers. I'd definitely put some sort of netting on top!