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Great Horned Owl

About Owl Pellets
11/02/18  Michael J. Gaylo

All birds of prey consume quantities of bone, feathers, and fur when eating prey.  Owls tend to swallow small prey such as voles, mice and shrews whole. Prey is swallowed head first and moves down the owl's esophagus and then through the proventriculus which is the glandular part of the stomach. Here, the owls food gets coated with digestive enzymes and then moves to the muscular part of the raptor’s digestive tract called the gizzard. After the soft tissue has been digested, the remaining bones, fur and/or feathers are rolled and compacted to form a pellet or casting. This is regurgitated by the owl several hours after eating or before the next meal.

Accuracy in making counts of prey items depends on the type of pellet that is being worked with.  Because of differences in feeding habits and physiology, hawks and owls produce pellets that differ in their ability to be examined quantitatively.  Owls usually swallow small prey whole and don’t take the time to pluck their prey.  Also their digestive tract does little or no damage to the bone consumed.  This results in pellets that usually contain whole skeletons that are relatively undamaged.  Hawks on the other hand, pluck their prey before eating and then tear it into small pieces before swallowing, consuming varying amounts of fur and feathers.  They also digest bones more completely than owls so that their pellets often contain little osseous remains.  Identification of prey species must be made by pairing incisors which are usually present.  Fairly accurate counts can be made in this manner by someone trained in their identification .

It isn’t known how many pellets a wild raptor produces per day so that accurate figures on daily intakes are unavailable.  However, they do yield information as to the type of prey consumed.   By comparing bones, feathers, and fur with the same material in an identified collection, identification of the dissected items is fairly easy.  In many cases if a large enough sample of pellets is examined it is possible to obtain a fairly accurate record of the diet of one raptor or the diet of a species.  It is also an indication of population densities and vulnerability of the prey species identified, since prey is taken in proportion to it’s relative density.

Hawks, Owls & Wildlife