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

Abstract

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.

Dietary shifts in two vultures after the demise of supplementary feeding stations: consequences of the EU sanitary legislation

“…As is habitual in scavenger diet studies and because bones rarely appeared in pellets, we did not calculate minimum numbers. Alternatively, we estimated the frequency of occurrence of each prey species (percentage of the total number of pellets in which the prey was detected) (see e.g., Hiraldo et al 1991b;Lambertucci et al 2009). Although pellet analyses may present some biases (in particular due to the underestimation of items with soft tissues) it is a valid procedure to compare diets of species having parallel food habits as is the case of scavengers (see Hiraldo et al 1991b;Kelly et al 2007, and references therein).…”

Taphonomy and dispersion of bones scavenged by New World vultures and caracaras in Northwestern Patagonia: implications for the formation of archaeological sites

“…Noteworthy is the existence of a high abundance of domestic livestock mammals: cow (Bos taurus), horse (Equus caballus), sheep, and exotic wild mammals: European hare, red deer (Cervus elaphus), and wild boar (Sus scrofa) hunted for sport (Novillo and Ojeda 2008;Lambertucci et al 2009). …”

“…The climate is cold with strong westerly winds and a significant west-east rainfall gradient due to the Pacific anticyclone and the topographic barrier of the Andean Cordillera, which generates drier conditions to the east . Phytogeographically, the area belongs to the Occidental District of the Patagonian unit, which is characterized by shrubby and grassy steppe with a vegetation cover about 50 %, constituted mainly by Stipa speciosa (Bcoirón amargo^), Stipa humilis (Bcoirón llama^), Senecio filaginoides (Bcata mora^), and Mulinum spinosum (Bneneo^) (León et al 1998). …”

“…Scavenger birds mostly feed on large ungulates but can include smaller vertebrates in their diets (del Hoyo et al 1994;DeVault et al 2004;Biondi et al 2005;Kelly et al 2007;Vargas et al 2007;Lambertucci et al 2009;Ballejo and De Santis 2013). These birds can transport and feed on carcass parts at nesting or roosting places on ledges of rocky cliffs and in trees, where bone accumulations can mix with carnivore or human-derived assemblages (Ballejo et al 2012;Marín-Arroyo and Margalida 2012).…”

Dealing with non-native species: what makes the difference in South America?

“…While a few positive impacts of introduced species have been recorded in South America (Jaksic 1998;Novaro et al 2000;Lambertucci et al 2009), negative effects widely range from the extinction of endemisms and the emergence of infectious diseases to large-scale alterations of entire habitats (e.g., Rodriguez 2001;Jaksic 1998;Jaksic et al 2002;Novillo and Ojeda 2008). The mongoose (Herpestes javanicus), introduced in northern South America to control rats and snakes on agricultural lands, quickly spread preying on endemic fauna and acting as a vector of rabies and leptospirosis (Ziller et al 2005), while the giant African snail (Achatina fulica) transmitted eosinophilic meningitis in Brazil and Colombia (Ziller et al 2005).…”