Diet of variable hawks Geranoaetus polyosoma (Quoy & Gaimard 1824) in Atacama Region, Chile

Abstract

The Variable Hawk (Geranoaetus polyosoma) is a raptor species distributed from Arica to Tierra del Fuego in Chile. It consumes small vertebrates and invertebrates, particularly insects and arachnids. The biological information of this species is scarce for northern Chile, particularly about their reproduction, diet, etc. We evaluated the diet of the Variable Hawk, by means of pellets collected between Vallenar to Copiapó, in Atacama region, a hyper-arid area. This information was compared with the available scientific literature in Chile and neighboring countries. Because of the environmental conditions of extreme aridity, we expect to find a low diversity of prey, characteristic of the raptors of arid ecosystems. In the case of the Variable Hawk populations from Atacama region, the most consumed species were reptilians (57,1%) corresponding to small lizards of the Liolaemus spp (30,4%), L. bisignatus (17%) and Callopiste maculatus (5,3%). Other prey corresponded to rodents (19.8%) and coleopterans of the genus Gyriosomus (18.9%). There was no positive correlation between frequency of prey and their body mass (r2= -0.267, p> 0.05) indicating that this raptor does not select their prey by body size. The biomass of reptiles in the diet (55.3%) was slightly higher than mammals (42.7%), but the largest individual contribution was given by Phyllotis darwini with 27.6%. Both the Simpson (SI = 0.1833) and the Shannon index (H ‘= 0.8463) indicate that this species consume a low diversity of prey, which is consistent with the others raptors that inhabit arid environments.