Diet of Black-chested Buzzard-Eagle (Geranoaetus melanoleucus) in a west–east transect in the ecotone of northern Patagonia

Abstract

The diet of Black-chested Buzzard-Eagle (Geranoaetus melanoleucus) was studied during 2002-2003 breeding season in five sites located on a west–east transect in the ecotone between the subantarctic forests and the Patagonian steppe, in Andean Río Negro Province, Argentina. This area is characterized by a heterogeneous habitat determined by a west–east decreasing precipitation gradient. We identified 525 preys from 271 pellets collected under perches or nests. Prey composition (considering the total sample) was: 51% rodents (mostly native sigmodontine rodents under 200 g), 25% lagomorphs, 3% other mammals, 8% birds, 1% reptiles, and 12% arthropods. Our results contrast with those of the rest of the studies on this bird made both in Chile and Argentina, where lagomorphs predominate in the diet and sigmodontine rodents made up a lesser proportion. Analyzing the diet from different localities, the western (more humid) sites presented rodent-dominated diets, whereas the eastern (more arid) ones presented lagomorph-dominated diets. We attribute these differences to the abundance of sigmodontine rodents in the more humid sites due to habitat heterogeneity, and to the eagle’s opportunistic feeding behaviour.