Owl pellets are composed of the indigestible materials of an owl's prey--including feathers, teeth, fur and some bones--and digestive fluids, shaped into slime-covered pellets. Such pellets are common to not only owls but to all birds of prey that swallow their food whole, including hawks and eagles.
Owl pellets will most often be brown or gray. Pellets will usually measure 1.5 to 3.5 inches long, depending on the size of the owl, and are usually coated in the fur of digestible animals. When a pellet is regurgitated, it is roughly the same shape as a particular owl's gizzard and can be spherical, oblong or plug-shaped.
The contents of an owl's pellets are key indicators of an owl's diet, which include small mammals or birds. The bones of mice, rats, rabbits, squirrels, voles and gophers have all been found in the pellets of various species of owl. As for other birds, owls have eaten doves, pigeons, grouse and even some varieties of songbird such as sparrows and warblers. Some species of owls have specialized diets that include fish, carrion or insects.
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Pellets are regurgitated by owls approximately 20 hours after eating. Owl intestines have weak digestive enzymes, which cannot break down hard-to-digest materials. Instead, these are held in an owl's gizzard while other, digestible, materials pass through. When the gizzard is full and a pellet ready to be ejected, an owl simply stretches its neck up and forward while opening its beak. The pellet is ejected without any retching. Ejecting a pellet in this manner scours parts of an owl's digestive tract.
Most adult owls will produce two pellets a day. Pellets can commonly be found underneath owls' favorite roosts, as this is where they rest to digest their prey. Young owls will usually not produce pellets, as their diet consists of predigested food regurgitated to them by their parents.
The pellets of owls are collected for a variety of purposes. Taxidermists wishing to reconstruct the skeletons of small mammals or birds extract bones from owl pellets. Industries also exist around owl-pellet collection for classroom or instructional use; the pellets are sanitized and individually packaged so that they might be dissected. Some scientists conduct research based on owl pellet contents.