A Curious Pellet From a Great Horned Owl (Bubo Virginianus)

One of the traditional methods of determining the dietary preferences of owls relies upon the identification of bony remains of prey contained in regur- gitated pellets. Discovery of a pellet containing a large, complete primary feather from an adult, male Ring-necked Pheasant (Phasianus colchicus) prompted us to examine in detail a small sample of pellets from a Great Horned Owl (Bubo virginianus). Our analyses of feather and hair remains in these pellets docu- mented the presence of three species of birds and two species of mammals, whereas bones in the pellets represented only mammals. This finding indicates an important bias that challenges the reliability of owl pellet studies making use of only osteological remains. Six egested pellets from a Great Horned Owl, Bubo virginianus (Gmelin, 1788), were collected on 13 April 2003 along the northeast side of Blue Marsh Lake, ca. 11 mi north of Reading, Penn Township, Berks County, PA. The pellets were scattered beneath a large black walnut tree (Juglans nigra Linne, 1753) along the edge of a windbreak of trees bordering a grassy, overgrown field just north of Old Church Road and west of Route 183. They are all believed to be from a single individual because of their proximity and their similar size and shape. One of these pellets (catalogue USNM 601957) is unusual because it contains a large (> 190 mm long when extended), complete primary (P-9) feather (Fig. 1) from the right wing of an adult, male Ring-necked Pheasant (Phasianus colchicus Linne, 1758). The pellet also contains large fragments of other feathers, although none with shaft diam- eters as great as the complete P-9. Other than these feathers, the pellet consists primarily of compacted hairs. No bones are apparent on the surface, nor were any revealed by digital x-ray. Our review of the literature on raptor pellets and our discussions with colleagues revealed no previous instances of an item as large as the primary feather being discovered incorporated into the body of a regurgitated pellet. The visual impact of USNM 601957, and the fact that no bones of pheasant were present, encouraged us to examine all of the pellets more closely, paying particular attention to the correspondence among incorpo- rated feathers, hairs, and osteological remains. We identified feathers by direct comparison with museum specimens and by use of microscopic 1