When owls eat their food, it goes straight into their stomachs, where it is digested by stomach acids and all digestible parts eventually come of the rear of the owl as ‘whitewash’. However, due to the diet of owls, some parts of their prey cannot be broken down, such as bones, fur, beaks etc. The owl therefore has to regurgitate these indigestible remains on a regular basis. These remains come out in an oval ball know as a pellet. These pellets can be found at nest sites or beneath favourite roosting spots and perches.
Pellets give conservationists valuable information about the diet of individual owls, and how they are surviving. Barn owls, for instance, should be eating about 75% short-tailed field vole in an ideal situation. But if pellets on a study of a pair of birds are shown to contain an average much lower than that, it indicates that the owls are not managing to catch their preferred prey and could point to low vole levels in their territory. This is normally associated with loss of rough grassland vole habitats, and we can then approach landowners in attempt to encourage an increase in these habitats to help this local pair of owls.
Owl pellets are also used by small mammal organisations, like the Mammal Society, as their contents give clues to the presence of rarer small mammals, such as harvest mice.