Pellet Formation in a Great Horned Owl: a Roentgenographic Study

IN the literature on owls, there has been much interest in the formation in the upper gastro-intestinal tract of pellets which contain indigestible material and which are subsequently regurgitated. This feature of gastrointestinal function has interested bird physiologists, and analysis of the pellets has been used to monitor feeding habits (Errington et al., 1940). Although pellet formation is not limited to the order Strigiformes, most information concerning this aspect of avian physiology comes from work on owls. Studies have centered on such problems as factors affecting the meal-pellet interval (Chitty, 1938), pellet analysis, physico-chemical properties of digestive juices, and anatomical distinctions between pellet forming and non-pellet forming birds (Guerin, 1928). It is possible from indirect evidence to make a reasonable estimate of the sequence of events involved in the 10 hour process of the formation of a pellet from the indigestible portion of an animal. A review of the available literature, however, fails to reveal an accurate account of events in vivo as seen by radiographic methods. The opportunity for such a study was afforded when a full-grown Great Horned Owl (Bubo virginianus) was received for study.