How do Vultures Fit into a Rewilding Continent?
According to Navarro and Pereira (see Chap. 1), the decline in the number of extensive livestock in Europe was 25 % between 1990 and 2010. From this assessment two interpretations are possible: on the one hand, the abandonment of traditional grazing involves a significant reduction in livestock and domestic food sources for vultures, but on the other hand, the landscape abandonment may contribute positively to the expansion of wild ungulate populations in many rural areas of Europe, notably in mountain ranges. Blázquez-Alvarez and Sánchez-Zapata (2009) showed that the number of wild ungulates hunted in Spain went from 60,000 in around 1980 to 200,000 in 2005. The current area of distribution occupied by wild ungulate species has also spread (e.g., 70–75 % of the Spanish territory, Sánchez-Zapata et al. 2010) such that up to six different species of ungulates can be found in some mountain areas. Similar trends can be found in other Mediterranean and temperate regions of Europe (Milner et al. 2006).
Increasingly larger populations of wild ungulates are allowing a return to natural diets of specialists and facultative scavenger species (see Moreno-Opo et al. 2007; Sánchez-Zapata et al. 2010). The availability of wild ungulate carcasses for vultures would increase even more if future rewilding processes lead to the expansion of large carnivores which would contribute a regular supply of random carcasses (Selva 2004; Blázquez-Alvarez and Sánchez-Zapata 2009). More important than the global availability of carcasses may be the ways in which the existence of large carnivores can change the temporal and spatial distribution of the resource and the associated consequences. It has been argued that predation can add stability to trophic networks buffering those oscillations linked to temporally-pulsed events of carrion availability such as those determined by climatic events, diseases and hunter-kills (Wilmers and Getz 2005; Wilmers and Post 2006). Currently, and because of persecution, wolves in European landscapes are restricted to forests and mountains, and therefore most of the species benefiting from predated animals are forest-living facultative scavengers (Selva 2004; Selva et al. 2003; 2005). It is expected, however, that in a more relaxed scenario carcasses of killed ungulates would also be available in open biomes, thus being available to large avian scavengers, and restoring the stability and the insurance of food chains and ecological processes (Wilmers and Getz 2005; Tylianakis et al. 2010).
A key question arises from a scenario of substitution of domestic by wild ungulates: can vulture populations survive in a future wilder scenario where most of the carcasses are provided by wild herbivores? Recent research performed in NorthEastern Spain by Margalida et al. (2011) based on the application of bio-inspired computational models revealed that this may be the case for high mountain areas where large and diverse populations of wild ungulates subsist. On the contrary, in low-altitude areas with higher humanization densities, wild herbivores are scarce and their populations would be insufficient to guarantee the long-term maintenance of avian scavenger populations such as those of griffon, Egyptian and bearded vultures. Therefore, these authors also suggest that in lowland areas of European Mediterranean regions, carrion-eaters will still be dependent on resources provided
Fig. 5.6 Cultural services provided by birds benefit local communities. The delight with the beauty of vultures alone or soaring in large group at their breeding areas and/or feeding at vulture restaurants confer a value to environment, and attract birdwatchers from all over the world translating this cultural service into significant incomes via “ecoturism”. (Photo credit: Jordi Bas)
by traditional extensive livestock and/or those supplies offered by conservation managers in vulture restaurants. From these results arise new questions for future research about how extensively rewilding should be facilitated, especially in those low-altitude humanized areas, in order to decrease vulture dependence on networks of large and fixed supplementary feeding stations.
The consumption of wild ungulate carcasses derived from hunting is not exempt of risk for avian scavengers. Birds ingesting pieces of hunting ammunition are exposed to lead intoxication (see review in Fisher et al. 2006; Mateo et al. 2007) to the extent that its incidence can be a serious threat to large-scale reintroduction projects such as that of the California condor in North America (Finkenlstein et al. (2012 and references therein). Lead levels are also very high in Europe, for instance Iberian griffon vultures show seasonal and spatial variations according to the rate of consumption of wild ungulates (García-Fernández et al. 2005). Moreover, carcasses resulting from hunting activities frequently accumulate at a few points at the end of hunting activities (Wilmers et al. 2003), which mimics the predictability offered by vulture restaurants and may result in similar negative effects (see above). Under a future scenario of a wilder Europe, we may promote two lines of action to curb the poisoning of scavengers: the consideration of a wilder Europe with zones limiting or lacking in hunting activities and in parallel the encouragement of the traditional extensive grazing currently under decline.
Fig. 5.7 Hotspots of abandonment and rewilding and distribution of the most important breeding areas for top scavenger: Giffon vultures and the endangered Egyptian, bearded and cinereous vultures. The map in the centre, relative to rewilding, shows areas categorized as “agriculture” in 2000 that are projected to become rewilded or afforested in 2030 with the CLUE model (see Chap. 1 for mapping method). The maps showing the scavenger distributions are based on information available in the Spanish Atlas of Breeding Birds (Del Moral and Martí 2004). (Species drawings: Juan Varela)