Factors Influencing Pellet Egestion and Gastric Ph in the Barn Owl

T HE volume o’ f literature considering the food habits of owls approaches prodigious proportions (see Earhart and Johnson, 1970). Much of this information has been derived from analysis of the pellets of non-digestible matter which these raptors egest periodically. A number of authors have reviewed this technique and its applications (Craighead and Craighead, 1956; Errington, 1930, 1932; Fisher, 1893, 1896; Glading, Tillotson and Selleck, 1943; Moon, 1940). In spite of the widespread interest in raptor-pellet analysis and application of this procedure for estimating food intake of these birds in the wild, very little information is available on the factors relative to the processes of pellet formation and egestion in birds of prey (Farner, 1960). The Great Horned Owl (Bubo virginianus) is the only owl for which pellet formation has been studied (Reed and Reed, 1928). Other papers considering pellet “formation” in owls have been concerned largely with the intervals between feeding and pellet egestion and have not dealt directly with the digestive processes involved in pellet formation or the factors which determine pellet egestion (Chitty, 1938; Howard, 1958; Sensenig, 1945). Two extensive life history studies of the Barn Owl (Tyto alba) by Guerin (1928) and Wallace (1948) offer some information relative to pellet formation and egestion in that species. It is the intent of this paper to present further information relative to the processes involved in pellet formation and egestion in the Barn Owl.