In preparation for the Central Ohio Owl Project, I have been collecting (and taking pictures of) owl pellets. Owls regularly regurgitate these parts of their prey that can't be digested; pellets usually contain hair, bones, and teeth, but can also include feathers, invertebrate exoskeletons, and other materials. They provide evidence of an owl's presence, even if the owl isn't currently using that roost site. The size of the owl pellet correlates with the size of the owl, although Barn Owls have particularly large pellets for their size.