Owl pellets are masses of bones, teeth, hair, feathers, scales, and insect

skeletons. They are produced and regurgitated, not only by owls, but also by hawks,

eagles, and other raptors which swallow their prey whole or in large pieces. The soft

parts of the prey are dissolved by proteolytic enzymes (protein digesters) and strong

acids which occur in high concentrations in the stomachs of raptors. The relatively

weak stomach muscles of the bird form the undigested fur, bones, feathers, etc. into

wet, slimy pellets. In this process, even the most fragile bones are usually preserved

unbroken. Because the pyloric opening of the stomach into the intestine is narrow,

only finely divided materials pass into the intestine. As a result, tiny bones only

occasionally pass through the digestive system. Each whole owl pellet usually

contains virtually complete skeletons of the animals which the owl ate the night

before the pellet was formed.