I tried it in my project and I found out that it is very easy to mirror part of your rig (including animation).
First finish the wing completely, mesh deformations, bones, etc... and animate it as you wish. After that step select the parent bone of your wing and duplicate it (ctr+D). Move the duplicated wing to left/right (depending the symmetry), by moving its own parent bone. Finally set the x scale to -1.0 (see the picture).
If the wings are part of bigger rig, re-assign the parent bone of each wing to appropriate parent bone from your rig's main body.
I hope that will help you.