If I was animating only the wings, I'd keep this in a single layer, and use a mixture of Flexi-bind and Bind Points where appropriate. When the animation will be simple and limited, keep the setup simple.
An argument could be made to separate the body from the wings (so, at least three layers or groups of art,) but this depends on how complicated or detailed you want the animation to be. You should ask: Does the head also move? Does the tail? Does it open its beak?
If this was a 'general use' character rig that performs many different actions throughout a story, I'd break it out into multiple layers. I'd use Link to isolate which bones in the rig affect which layer of character. I'd likely combine this with Bind Points for any points that need to be locked to specific bones. Just mentioning this to help with the decision.
Hope this helps.
