Allochthonous and autochthonous components from gizzard grit of Theristicus melanopis in anthropogenic pastures of southern chile

Abstract

Allochthonous and autochthonous components from gizzard grit of ABSTRACTNumerous vertebrates, and in particular birds, ingest stones (geo-gastrolites) to favour the breakdown and digestion of food in the muscular stomachs. Between 1993 and 1994 we evaluated the quantity, relative abundance and quality of autochthonous (geo-gastrolites) and allochthonous (pieces of glass) components of the grit in gizzards of black-faced ibis (Theristicus melanopis) inhabiting the pastures of southern Chile. Grit elements were present in 32 out of 48 (66,7%) of all gizzard analysed. A total of 572 particles were recorded from which, 69.1% corresponded to autochthonous elements and 27.8% were allochthonous particles. Both components are similar in shape; however glass contributes considerably more in terms of mass. Gender differences reveal that females consume a signifi cantly greater number of allochthonous elements than males. We postulate the hypothesis that, due to their high energy requirements, females ingest more pieces of glass to facilitate the breakdown and digestion of food with a limited nutritional value, thus increasing their reproductive success. KEYWORDS:Black-faced ibis, glasses, gastrolites, pastures, south Chile RESUMENNumerosos vertebrados y en particular las aves, ingieren piedras (gastrolitos) para favorecer la maceración y la digestión del alimento en los estómagos musculares. Entre 1993 y 1994 evaluamos la cantidad, abundancia relativa y calidad de componentes autóctonos (piedras) y alóctonos (trozos de vidrios) de los gastrolitos presentes en las mollejas de bandurrias (Theristicus melanopis) en praderas agrícolas del sur de Chile. Los gastrolitos se presentaron en 32 de las 48 (66,7%) mollejas analizadas. Se registró un total de 572 partículas de las cuales 69,1% fueron elementos autóctonos y 27,8% partículas alóctonas. Ambos componentes no difi rieren en la forma pero los vidrios aportaron signifi cativamente mayor masa. Las hembras consumieron un número signifi cativamente mayor de elementos alóctonos que los machos. Postulamos la hipótesis que las hembras, con alto requerimiento energético, ingieren más trozos de vidrio para incrementar la efi ciencia de maceración y digestión de alimentos con reducido valor nutricional, lo que les permitiría incrementar su éxito reproductivo.