I also think that the "feather" is a leaf, an oak likely.  If you look at the original image on findagrave memorial 140651431 and view the enlarge image in color, there are many acorns and other oak leaves around the stone.  Additionally there is the cap of an acorn shown above the eagle's right wing [left side of image] and the object above the "feather" seems to be several acorn caps and twigs being clearly brown and separate not the blueish bronze color of the eagle.