Taphonomic investigations of owl pellets

Owls are important consumers of small vertebrates, and because they regurgitate pellets rich in bone, they may be important potential contributors of the concentrated remains of small vertebrates to the fossil record. Owls of three sizes, the large great horned owl (Bubo virginianus), the medium-sized barn owl (Tyto alba), and the small screech owl (Otus asio), were fed a common diet of mice. The bony contents of the pellets were analyzed to determine the amount of bone loss by digestion, bone completeness, and sites of bone breakage. For all three species, only about half the number of bones ingested were recovered in the pellets. Mandibles and femora were most abundant, and pelves and scapulae were the least abundant. Screech owls broke 80% of the cranial and limb elements, barn owls only 30%. Skulls fared poorly in great horned and screech owl pellets, while barn owls returned 80% of the skulls intact, with only the caudal portion of the cranium damaged; barn owls also returned articulated strings of vertebrae and complete paws. These results provide a baseline for the recognition of owls as agents of accumulation of small bones in the fossil record and suggest that the actions of ancient predators may be revealed by species-specific patterns of bone destruction of an assemblage of fossil prey species.