Food Habits of the Roadside Hawk (Buteo magnirostris) During the Nonbreeding Season in the Southeastern Pampas of Argentina

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Studies of raptors' diet are important for understanding the ecological relationships of the raptors themselves, as well as for assessing the influence of these predators on community ecology (Marti et al. 2007). Although there is abundant information about food habits of raptor species around the world, data on the trophic ecology of neotropical raptors are scarce and the diets of many species are poorly known (del Hoyo et al. 1994, Bierregaard 1998, Bó et al. 2007). The Roadside Hawk (Buteo magnirostris) is a widespread raptor species of Central and South America, ranging from northern Mexico to Río Negro Valley in central Argentina (Thiollay 1994). This medium-sized raptor usually inhabits woodlands and forest edges and, to a lesser extent, open fields near woodlands (Canevari et al. 1991). Near the southern boundary of its range, in the pampas of Buenos Aires Province (Argentina), this raptor is also associated with agroecosystems and grasslands (Narosky and Di Giacomo 1993, Mazar-Barnett and Pearman 2001). Despite being a common species with broad distribution, the Roadside Hawk has been little studied and information about its food habits is scarce and mostly limited to qualitative and anecdotal information (e.g., Haverschmidt 1962, Massoia 1988). In two studies, the diet of Roadside Hawks was quantitatively analyzed. Panasci and Whitacre (2000) reported breeding-season diet in Guatemala through direct observation of nests, and found that the Roadside Hawk delivered mainly small vertebrates (.90%; mainly lizards, frogs, and rodents) to the nest. However, Beltzer (1990) analyzed stomach contents of 22 Roadside Hawks in Argentina throughout one year, and determined that they consumed mostly insects (77%, mainly orthopterans). The objectives of our study were to quantitatively describe the diet of the Roadside Hawk and to estimate its food-niche breadth during the nonbreeding season in Argentina.