Hello fellow taxidermists! Question for you professionals. While working on a Pintail, I noticed some stains on the breast feathers while blow drying the bird. I rewashed a few times (Using Dawn, laundry detergent and stain remover), letting the bird sit in each trying both warm and cold water and nothing seems to have lifted the stains. They almost look like the pattern from the flank feathers has spread onto them. Is this possible or is it some form of stain? Should I try to remove the stain? If so, what would you recommend I do to try removing them? Pic is of the stain. All help is appreciated!