The following quote is from Crawford:
Long filoplumes (Lf). Just before he died , Dr. W.H McGibbon was working with a trait that he called long filoplumes(Somes, 1978a). The filoplumes in the fluff areas of the body were 1-10 cm longer than the adjacent definitive feathers. Somes(unpublished), has also observed this trait in a line of birds at University of Connecticut which filoplumes project beyond the plumulus and contour feathers. Although inheritance studies on this trait are unpublished, McGibbon claimed that this trait was inherited as an autosomal dominant, and he applied the gene symbol Lf to it.
