Trophic Niche Overlap Between Raptorial Scavengers in Patagonia: New Support for the Competition Hypothesis

BALLEJO F; LAMBERTUCCI, S. A.; DE SANTIS, L

Bariloche

Congreso; I Worldwide Raptor Conference; 2013

Animals sharing resources typically use different foraging strategies to decrease potential competition. Avian scavengers can segregate resources into different space and time scales. However, when the species do not co-evolve, such segregation may initially require competition. We studied the trophic niche overlap of three species of obligate raptorial scavengers, one of which recently increased in abundance. We conducted our study in northwestern Patagonia, where there are several scavengers, Andean Condors (Vultur gryphus), Turkey Vultures (Cathartes aura) and Black Vultures (Coragyps atratus) are the main consumers of carcasses. Black Vultures arrived in the area relatively recently and expanded following human activities. Competition between Black Vultures and threatened Andean Condors has been suggested. Therefore, it is important to understand trophic overlap between these species. We collected pellets (n = 440) from roosts of both vultures species. We determined all taxa consumed and estimated food niche breadth (Levins Standardized Index) and diet similarity (Pianka overlap index). We compared results with data on the diet of Andean Condors from the literature. Our results indicate Turkey Vultures have greater amplitude in the selection of carcasses and, incorporating livestock, fish, reptiles, carnivores, mice and a great number of birds in their diets. Although Black Vultures included arthropods in their diet, they fed primarily on introduced ungulates, overlapping more with condor diets at roosts far from urban centers. These two species may switch their competitive advantages due to size when Black Vultures are abundant, and can colonize the carrion. Because these species share resources, human activities that positively affect the abundances of Black Vultures could increase competition, with the possible implications for conservation of Andean Condors.