My gut feeling is it will be difficult to do this sort of pattern on a standard sized mini. (Note that I have no idea how big this mini actually is.)
If you want something this intricate, making a decal might be best, at least for the small feathers.
If you want something similar but not necessarily so complex, I would go about it this way on the main body: Start by painting in the large details (the beak, the green base coat, the eye). Once this is done, assess how much green there is and see how fine (or crazy) you want to get.
The small feathers in the middle of the helicopter remind me of scales. You can probably therefore adapt scale painting techniques to paint in the small feathers. The shadows/highlights might need to be adjusted over standard scales.
Larger feathers can be painted in the usual manner (not that I'm exactly sure what this would be). (I assume there would be larger feathers on the "wings," if they exist, or towards the tail.)
