Comparative diet of the Variable hawk Geranoaetus polyosoma (Quoy & Gaimard, 1824) and the Great horned owl Bubo magellanicus (Lesson, 1828) in the altiplano of the Region of Tarapacá, Chile

Abstract

Between fall and winter of 2017, three field trips were carried out in the altiplano of the Region of Tarapacá. During these field trips, pellets of Geranoaetus polyosoma (Variable Hawk) and Bubo magellanicus (Great Horned Owl) were collected, in order to describe and compare their diets. The diet of G. polyosoma was characterized by a high content of invertebrates of the Coleoptera Order (65.3% frequency), in addition to three species of rodents (1.4 to 12.5% frequency; 4.4 to 43.5% abundance), lizards (9.7% frequency; 39.1% abundance) and invertebrates of the Bothriuridae Family. Additionally, South American camelid hair was detected in 16.7% of the pellets, which could be due to a carrion behavior. In contrast, the diet of B. magellanicus consisted mainly on rodents and marsupials (six species, with 0.8 to 37.8% of frequency and 0.5 to 52.8% of abundance), highlighting Phyllotis xanthopygus, prey that also was the dominant in the diet of G. polyosoma. To a lesser extent, invertebrates (3.9 to 8.7% frequency), lizards (5.5% frequency; 3.8% abundance) and birds (3.9% frequency; 2.8 % abundance) were detected. Comparing the diet of B. magellanicus and the availability of small mammals in the environment, a preference for Phyllotis xanthopygus and a notorious evasion in the consumption of Akodon albiventer were observed, plus a similar consumption to the environmental availability of Abrocoma cinerea and Abrothrix andina. In relation to the trophic niche breadth, B. magellanicus presented a greater dietary diversity compared to G. polyosoma (3.1 and 2.8 respectively), with a niche overlap of 78.9%.