Owls feed on a diet of small- to medium-sized mammals, birds, and insects. Sooty Owls feed particularly on tree-dwelling mammals such as gliders, while other species prefer land-dwelling mammals or lizards. Like most birds, they’re unable to chew and will mostly eat their prey whole, or tear off pieces.
Owls, like other raptors, regurgitate the non-nutritious parts of their prey. Several hours after eating they'll produce a pellet from their gizzards and then be ready to eat again.
While the idea of trawling through owl vomit might be nausea-inducing for some, ecologists can tell a lot about an ecosystem from these pellets.