Spatial and temporal patterns in the diet of the Andean condor: ecological replacement of native fauna by exotic species

The development of conservation strategies to protect viable populations of scavenging birds requires the existence of adequate and safe food supplies in the wild. Early reports on Andean condors Vultur gryphus diet recorded guanacos and rheas, the dominant herbivores since the Pleistocene, as their main food in Patagonia. However, in the past century, guanaco and rhea populations have notably decreased as a consequence of introduced livestock, and other exotic mammals have colonized the region. We study the spatial and temporal variation of the condors' diet to determine which species are being consumed by condors, and to test whether native herbivores still have a role as a food source. We analysed 371 pellets (517 prey items), collected along 500 km in northwestern Patagonia, Argentina. Our study shows that the Andean condor depends heavily (98.5%) on exotic herbivores. Their diet was made up of c. 51% sheep/goat, 24% hare/rabbit, 17% red deer and 6% cow/horse, with only 2% other mammal species. Samples from locations surveyed after 12-15 years showed a diet shift coincident with the local tendencies in the food source. The diet composition of condors using roosts within the same zone was very similar, which suggests that they may be feeding from the same area. Thus, unhealthy carcasses could impact the entire local populations. Our results show the abundance of the invasive species in northwestern Patagonia and support the idea that native mega-herbivores are ecologically extinct in this area. Exotic species management can have a decisive impact on scavenger's survival. It is necessary to apply a strategy that includes public environmental education about the problems of scavengers (e.g. use of poison, veterinary medicines and lead bullets), and a serious productive plan, including native species as a suitable source of economic development.