Goto top menu bar > layers > transparency > add alpha channel back to your image, now use the pink eraser tool to make the part around the feathers invisible (you'll see checkbox background to indicate it's invisible when saved and loaded into game / modelviewer)
There is another more involved way via graphics converter 3 if you need to bring back all the original alpha (invisible areas) before you edited the image but I don't think you need that here so Ill post that another time.
I use photoshop but thank you with that direction I was able to figure it out