Numerous 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 significantly 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.