Pellets are regurgitated indigestible matter. Owls are the most well known producers of pellets, often found near roost and nest sites. But many birds produce them, including Rooks. They are most commonly found below the communal nesting areas, known as rookeries, orin fields where Rooks have been feeding. As Rooks largely feed on the ground, probing for insects and plant material with their peg-shaped bills, the pellets largely consist of undigested plant material (especially seed husks) and small stones, but may also contain bone fragments and feathers. They are about 3.5x1.5cm and are less elongated than Carrion Crow pellets (looking a bit like owl pellets).