Many kinds of birds — from herons to hawks (and all kinds of raptors, including owls), even shorebirds and fish-eaters like kingfishers — regurgitate pellets. The digestive systems of these birds have to deal with bones, scales, fur, or feathers. So the bird’s gizzard performs a kind of sorting operation. Soft tissues pass through to be digested, while indigestible sharp and hazardous bits are formed into an oval mass, or pellet. They pass back up the digestive system and are regurgitated a few hours later.
A Short-eared Owl casts a pellet:
And a Long-eared Owl does the same:
See the tiny bone that is expelled at the same time?
Found on the ground:
Barn Owl and Tawny Owl pellets - SteveLeoEvans - FCC
A pellet, close up --
Bethany Weeks - FCC
Examining an owl pellet - classroom forensics!
Lester Public Library - FCC
Listen to a BirdNote show called Examining Owl Pellets.
All photos © Gregg Thompson, unless otherwise noted. Thanks, Gregg!