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Revista Chilena de Historia Natural 78 (3): 425-439, 2005
Dietary response of three raptor species to an introduced prey in Patagonia
Predators with strong functional responses may be able to help stabilize prey population levels. This is worth noting mainly in the case of introduced prey, whose impact on native ecosystems often involves significant economic and environmental damage. The current Patagonian situation is critical with respect to introduced species. Previous studies have shown that native vertebrate predators are able to change their feeding patterns, switching from native to exotic prey. We assessed the food habits of the grey buzzard-eagle (Geranoaetus melanoleucus), the Magellanic horned owl (Bubo magellanicus), and the red-backed hawk (Buteo polyosoma), the three most important avian predators of the introduced European hare (Lepus europaeus) in north-western Patagonia. We analysed 321, 115 and 78 eagle, owl, and hawk pellets respectively. We evaluated their functional responses to hare densities and compared their diets between different sites. Sigmodontine rodents were the hawk’s and owl’s main prey, followed by the tuco-tuco (Ctenomys spp.). The eagle consumed mainly European hares and then tuco-tucos, showing a significant functional response to the introduced prey. This raptor also had different diets in sites with high and low hare density. The other two raptors did not show a significant functional response to hare densities. However, the hawk’s diet varied according to geographic location. We conclude that eagles and hawks are generalist predators, whereas the owl tends to specialize on small mammals. The changes in the eagle’s diet in relation to European hare densities provide the potential to contribute to regulate the hare population.
Key words:
functional response, raptors, grey buzzard-eagle, red  backed hawk, Magellanic owl, European hare, Patagonia

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