It depends on how detailed you want it.
When rigging, you want to place bones where there actually are bones in real life. For example: http://hippie.nu/~unicorn/tut/img/ba...ing-bones.jpeg
If you wanted control over the feathers, you would need to put extra bones in them. Or if you really wanted to go crazy, use nCloth or some other dynamics system
Imagination is more important than knowledge.