I have a bantam Brahma and noticed yesterday that she was missing a few feathers on her neck. Today it is worse. I'm worried my other 2 hens are picking on her. They are about 18 weeks old and I've had all three of them since they were a day old. What's going on? Do I need to separate them? My other 2 are an EE and Barred Rock. Or could something else be going on? I took a few pictures.