I have been modeling a poly character. I made the wings separately from the model's body. Then I joined them using Ctrl+J as a union modifier making the wings disappear. The wings have their own armature, separate from the Rigify armature that is used on the body.
When entering Pose mode and moving the Rigify rig around the wings which were initially two separate parts that got joined together, get pulled apart into their original pieces even tho they have been joined into one object. (I couldn't use union as it would suck the wings into themselves).